1.
Egg as food
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Eggs are laid by female animals of many different species, including birds, reptiles, amphibians, mammals, and fish, and have been eaten by humans for thousands of years. Bird and reptile eggs consist of an eggshell, albumen. The most popular choice for egg consumption are chicken eggs, other popular choices for egg consumption are duck, quail, roe, and caviar. Egg yolks and whole eggs store significant amounts of protein and choline, due to their protein content, the United States Department of Agriculture categorizes eggs as Meats within the Food Guide Pyramid. Despite the nutritional value of eggs, there are potential health issues arising from egg quality, storage. Chickens and other egg-laying creatures are widely kept throughout the world, in 2009, an estimated 62.1 million metric tons of eggs were produced worldwide from a total laying flock of approximately 6.4 billion hens. There are issues of variation in demand and expectation, as well as current debates concerning methods of mass production. In 2012, the European Union banned battery husbandry of chickens, bird eggs have been valuable foodstuffs since prehistory, in both hunting societies and more recent cultures where birds were domesticated. The chicken was probably domesticated for its eggs before 7500 BCE, chickens were brought to Sumer and Egypt by 1500 BCE, and arrived in Greece around 800 BCE, where the quail had been the primary source of eggs. In Thebes, Egypt, the tomb of Haremhab, built about 1420 BCE, shows a depiction of a man carrying bowls of ostrich eggs and other large eggs, presumably those of the pelican, as offerings. In ancient Rome, eggs were preserved using a number of methods, the Romans crushed the shells in their plates to prevent evil spirits from hiding there. In the Middle Ages, eggs were forbidden during Lent because of their richness, the word mayonnaise possibly was derived from moyeu, the medieval French word for the yolk, meaning center or hub. Egg scrambled with acidic fruit juices were popular in France in the 17th century, the dried egg industry developed in the 19th century, before the rise of the frozen egg industry. In 1878, a company in St. Louis, Missouri started to transform egg yolk and white into a light-brown, the production of dried eggs significantly expanded during World War II, for use by the United States Armed Forces and its allies. In 1911, the egg carton was invented by Joseph Coyle in Smithers, British Columbia, early egg cartons were made of paper. Bird eggs are a food and one of the most versatile ingredients used in cooking. They are important in many branches of the food industry. The most commonly used bird eggs are those from the chicken, duck and goose eggs, and smaller eggs, such as quail eggs, are occasionally used as a gourmet ingredient in western countries
2.
Bird
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Birds, a subgroup of Reptiles, are the last living examples of Dinosaurs. Birds live worldwide and range in size from the 5 cm bee hummingbird to the 2.75 m ostrich. They rank as the class of tetrapods with the most living species, at ten thousand. Birds are the closest living relatives of crocodilians, the fossil record indicates that birds evolved from feathered ancestors within the theropod group of saurischian dinosaurs. True birds first appeared during the Cretaceous period, around 100 million years ago, Birds, especially those in the southern continents, survived this event and then migrated to other parts of the world while diversifying during periods of global cooling. Primitive bird-like dinosaurs that lie outside class Aves proper, in the broader group Avialae, have been found dating back to the mid-Jurassic period, around 170 million years ago. Birds have wings which are more or less developed depending on the species, the digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have evolved for swimming. Many species annually migrate great distances, Birds are social, communicating with visual signals, calls, and bird songs, and participating in such social behaviours as cooperative breeding and hunting, flocking, and mobbing of predators. The vast majority of species are socially monogamous, usually for one breeding season at a time, sometimes for years. Other species have breeding systems that are polygynous or, rarely, Birds produce offspring by laying eggs which are fertilised through sexual reproduction. They are usually laid in a nest and incubated by the parents, most birds have an extended period of parental care after hatching. Some birds, such as hens, lay eggs even when not fertilised, songbirds, parrots, and other species are popular as pets. Guano is harvested for use as a fertiliser, Birds prominently figure throughout human culture. About 120–130 species have become extinct due to human activity since the 17th century, human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational birdwatching is an important part of the ecotourism industry, the first classification of birds was developed by Francis Willughby and John Ray in their 1676 volume Ornithologiae. Carl Linnaeus modified that work in 1758 to devise the taxonomic classification system currently in use, Birds are categorised as the biological class Aves in Linnaean taxonomy. Phylogenetic taxonomy places Aves in the dinosaur clade Theropoda, Aves and a sister group, the clade Crocodilia, contain the only living representatives of the reptile clade Archosauria
3.
Turtle
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Turtles are reptiles of the order Testudines characterised by a special bony or cartilaginous shell developed from their ribs and acting as a shield. Turtle may refer to the order as a whole or to fresh-water, the order Testudines includes both extant and extinct species. The earliest known members of this date from 157 million years ago, making turtles one of the oldest reptile groups. Of the 327 known species alive today, some are highly endangered, turtles are ectotherms—animals commonly called cold-blooded—meaning that their internal temperature varies according to the ambient environment. However, because of their metabolic rate, leatherback sea turtles have a body temperature that is noticeably higher than that of the surrounding water. Turtles are classified as amniotes, along with reptiles, birds. Like other amniotes, turtles breathe air and do not lay eggs underwater, Chelonia is based on the Greek word χελώνη chelone tortoise, turtle, also denoting armor or interlocking shields, testudines, on the other hand, is based on the Latin word testudo tortoise. Turtle may either refer to the order as a whole, or to particular turtles that make up a form taxon that is not monophyletic, the meaning of the word turtle differs from region to region. In North America, all chelonians are commonly called turtles, including terrapins, in Great Britain, the word turtle is used for sea-dwelling species, but not for tortoises. The term tortoise usually refers to any land-dwelling, non-swimming chelonian, most land-dwelling chelonians are in the Testudinidae family, only one of the 14 extant turtle families. Terrapin is used to describe several species of small, edible, hard-shell turtles, typically found in brackish waters. Some languages do not have this distinction, as all of these are referred to by the same name, for example, in Spanish, the word tortuga is used for turtles, tortoises, and terrapins. A sea-dwelling turtle is tortuga marina, a freshwater species tortuga de río, the largest living chelonian is the leatherback sea turtle, which reaches a shell length of 200 cm and can reach a weight of over 900 kg. Freshwater turtles are generally smaller, but with the largest species, the Asian softshell turtle Pelochelys cantorii, a few individuals have been reported up to 200 cm. This dwarfs even the better-known alligator snapping turtle, the largest chelonian in North America and they became extinct at the same time as the appearance of man, and it is assumed humans hunted them for food. The only surviving giant tortoises are on the Seychelles and Galápagos Islands and can grow to over 130 cm in length, the largest ever chelonian was Archelon ischyros, a Late Cretaceous sea turtle known to have been up to 4.6 m long. The smallest turtle is the speckled padloper tortoise of South Africa and it measures no more than 8 cm in length and weighs about 140 g. Two other species of turtles are the American mud turtles
4.
Chondrichthyes
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The class is divided into two subclasses, Elasmobranchii and Holocephali. Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates, the notochord, which is present in the young, is gradually replaced by cartilage. Chondrichthyans also lack ribs, so if they leave water, the larger species own body weight would crush their internal organs long before they would suffocate, as they do not have bone marrow, red blood cells are produced in the spleen and the epigonal organ. They are also produced in the Leydigs organ, which is found in certain cartilaginous fishes. The subclass Holocephali, which is a specialized group, lacks both the Leydigs and epigonal organs. In most species, all dermal denticles are oriented in one direction, making the skin feel very smooth if rubbed in one direction, originally, the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. In later forms, each pair of fins became ventrally connected in the middle when scapulocoracoid, in rays, the pectoral fins have connected to the head and are very flexible. One of the characteristics present in most sharks is the heterocercal tail. Chondrichthyans have toothlike scales called dermal denticles or placoid scales, denticles provide two functions, protection and in most cases, streamlining. Mucous glands exist in species as well. This is most likely an evolved characteristic, which means there is not necessarily a connection between the teeth and the original dermal scales. The old placoderms did not have teeth at all, but had sharp bony plates in their mouth, thus, it is unknown whether the dermal or oral teeth evolved first. Nor is it sure how many times it has happened if it out to be the case. However, there is no evidence of this at the moment, all chondrichthyans breathe through five to seven pairs of gills, depending on the species. However, this is only a rule and many species differ. A spiracle is a hole found behind each eye. These can be tiny and circular, such as found on the shark, to extended and slit-like. Many larger, pelagic species, such as the mackerel sharks, like all other jawed vertebrates, members of Chondrichthyes have an adaptive immune system
5.
Cephalopod
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A cephalopod is any member of the molluscan class Cephalopoda. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, fishermen sometimes call them inkfish, referring to their common ability to squirt ink. The study of cephalopods is a branch of known as teuthology. Cephalopods became dominant during the Ordovician period, represented by primitive nautiloids, the class now contains two, only distantly related, extant subclasses, Coleoidea, which includes octopuses, squid, and cuttlefish, and Nautiloidea, represented by Nautilus and Allonautilus. In the Coleoidea, the shell has been internalized or is absent, whereas in the Nautiloidea. About 800 living species of cephalopods have been identified, two important extinct taxa are the Ammonoidea and Belemnoidea. There are over 800 extant species of cephalopod, although new species continue to be described, an estimated 11,000 extinct taxa have been described, although the soft-bodied nature of cephalopods means they are not easily fossilised. Cephalopods are found in all the oceans of Earth, none of them can tolerate freshwater, but the brief squid, Lolliguncula brevis, found in Chesapeake Bay, is a notable partial exception in that it tolerates brackish water. Cephalopods are thought to be unable to live in due to multiple biochemical constraints. Cephalopods occupy most of the depth of the ocean, from the plain to the sea surface. Their diversity is greatest near the equator and decreases towards the poles, Cephalopods are widely regarded as the most intelligent of the invertebrates, and have well developed senses and large brains. The nervous system of cephalopods is the most complex of the invertebrates, the brain is protected in a cartilaginous cranium. Cephalopods have also known to climb out of their aquaria, maneuver a distance of the lab floor, enter another aquarium to feed on the crabs. Cephalopods are social creatures, when isolated from their own kind, some cephalopods are able to fly through the air for distances of up to 50 m. While cephalopods are not particularly aerodynamic, they achieve these impressive ranges by jet-propulsion, the animals spread their fins and tentacles to form wings and actively control lift force with body posture. Cephalopods have advanced vision, can detect gravity with statocysts, and have a variety of sense organs. Octopuses use their arms to explore their environment and can use them for depth perception, most cephalopods rely on vision to detect predators and prey, and to communicate with one another. Consequently, cephalopod vision is acute, training experiments have shown that the octopus can distinguish the brightness, size, shape
6.
Lepidoptera
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The Lepidoptera is an order of insects that includes moths and butterflies. 180,000 species of Lepidoptera are described, in 126 families and 46 superfamilies and it is one of the most widespread and widely recognizable insect orders in the world. The term was coined by Linnaeus in 1735 and is derived from Ancient Greek λεπίδος, the Lepidoptera show many variations of the basic body structure that have evolved to gain advantages in lifestyle and distribution. Recent estimates suggest the order may have more species than earlier thought, and is among the four most speciose orders, along with the Hymenoptera, Diptera, and Coleoptera. Lepidopteran species are characterized by more than three derived features, some of the most apparent being the scales covering their bodies and wings, the scales are modified, flattened hairs, and give butterflies and moths their extraordinary variety of colors and patterns. Almost all species have some form of wings, except for a few that have reduced wings or are wingless. Like most other insects, butterflies and moths are holometabolous, meaning they undergo complete metamorphosis, mating and the laying of eggs are carried out by adults, normally near or on host plants for the larvae. As they grow, these change in appearance, going through a series of stages called instars. Once fully matured, the larva develops into a pupa A few butterflies and many species spin a silk case or cocoon prior to pupating, while others do not. A butterfly pupa, called a chrysalis, has a hard skin, once the pupa has completed its metamorphosis, a sexually mature adult emerges. Accordingly, this is the most recognized and popular of insect orders with many involved in the observation, study, collection, rearing of. A person who collects or studies this order is referred to as a lepidopterist, in many species, the female may produce from 200 to 600 eggs, while in others, the number may approach 30,000 eggs in one day. The caterpillars hatching from eggs can cause damage to large quantities of crops. Many moth and butterfly species are of economic interest by virtue of their role as pollinators, the word Lepidoptera comes from the Latin word for scaly wing, from the Ancient Greek λεπίς meaning scale and πτερόν meaning wing. The origins of the common names butterfly and moth are varied, the English word butterfly is from Old English buttorfleoge, with many variations in spelling. Other than that, the origin is unknown, although it could be derived from the yellow color of many species wings suggesting the color of butter. The species of Heterocera are commonly called moths, the origins of the English word moth are more clear, deriving from the Old English moððe from Common Germanic. The Lepidoptera are among the most successful groups of insects, among the most northern dwelling species of butterflies and moths is the Arctic Apollo, which is found in the Arctic Circle in northeastern Yakutia, at an altitude of 1500 m above sea level
7.
Zygote
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A zygote, is an eukaryotic cell formed by a fertilization event between two gametes. The zygotes genome is a combination of the DNA in each gamete, in multicellular organisms, the zygote is the earliest developmental stage. In single-celled organisms, the zygote can divide asexually by mitosis to produce identical offspring, oscar Hertwig and Richard Hertwig made some of the first discoveries on animal zygote formation. In fungi, the fusion of haploid cells is called karyogamy. The result of karyogamy is a diploid cell called a zygote or zygospore and this cell may then enter meiosis or mitosis depending on the life cycle of the species. In plants, the zygote may be polyploid if fertilization occurs between meiotically unreduced gametes, in land plants, the zygote is formed within a chamber called the archegonium. In seedless plants, the archegonium is usually flask-shaped, with a long hollow neck through which the cell enters. As the zygote divides and grows, it does so inside the archegonium, in human fertilization, a release ovum and a haploid sperm cell —combine to form a single 2n diploid cell called the zygote. The other product of meiosis is the polar body with only chromosomes. In the fertilized daughter, DNA is then replicated in the two separate pronuclei derived from the sperm and ovum, making the zygotes chromosome number temporarily 4n diploid. After approximately 30 hours from the time of fertilization, fusion of the pronuclei, between the stages of fertilization and implantation, the developing human is a preimplantation conceptus. However, the National Institute of Health has made the determination that the classification of pre-implantation embryo is still correct. After fertilization, the travels down the oviduct towards the uterus while continuing to divide mitotically without actually increasing in size. After four divisions, the conceptus consists of 16 blastomeres, through the processes of compaction, cell division, and blastulation, the conceptus takes the form of the blastocyst by the fifth day of development, just as it approaches the site of implantation. When the blastocyst hatches from the zona pellucida, it can implant in the lining of the uterus. The human zygote has been edited in experiments designed to cure inherited diseases. In the amoeba, reproduction occurs by division of the parent cell
8.
Animal
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Animals are multicellular, eukaryotic organisms of the kingdom Animalia. The animal kingdom emerged as a clade within Apoikozoa as the group to the choanoflagellates. Animals are motile, meaning they can move spontaneously and independently at some point in their lives and their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later in their lives. All animals are heterotrophs, they must ingest other organisms or their products for sustenance, most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. Animals can be divided broadly into vertebrates and invertebrates, vertebrates have a backbone or spine, and amount to less than five percent of all described animal species. They include fish, amphibians, reptiles, birds and mammals, the remaining animals are the invertebrates, which lack a backbone. These include molluscs, arthropods, annelids, nematodes, flatworms, cnidarians, ctenophores, the study of animals is called zoology. The word animal comes from the Latin animalis, meaning having breath, the biological definition of the word refers to all members of the kingdom Animalia, encompassing creatures as diverse as sponges, jellyfish, insects, and humans. Aristotle divided the world between animals and plants, and this was followed by Carl Linnaeus, in the first hierarchical classification. In Linnaeuss original scheme, the animals were one of three kingdoms, divided into the classes of Vermes, Insecta, Pisces, Amphibia, Aves, and Mammalia. Since then the last four have all been subsumed into a single phylum, in 1874, Ernst Haeckel divided the animal kingdom into two subkingdoms, Metazoa and Protozoa. The protozoa were later moved to the kingdom Protista, leaving only the metazoa, thus Metazoa is now considered a synonym of Animalia. Animals have several characteristics that set apart from other living things. Animals are eukaryotic and multicellular, which separates them from bacteria and they are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae. They are also distinguished from plants, algae, and fungi by lacking cell walls. All animals are motile, if only at life stages. In most animals, embryos pass through a stage, which is a characteristic exclusive to animals. With a few exceptions, most notably the sponges and Placozoa and these include muscles, which are able to contract and control locomotion, and nerve tissues, which send and process signals
9.
Embryo
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An embryo is an early stage of development of a multicellular diploid eukaryotic organism. In general, in organisms that reproduce sexually, an embryo develops from a zygote, the zygote possesses half the DNA of each of its two parents. In plants, animals, and some protists, the zygote will begin to divide by mitosis to produce a multicellular organism, the result of this process is an embryo. First attested in English in the mid-14c, the word embryon derives from Medieval Latin embryo, itself from Greek ἔμβρυον, lit. Young one, which is the neuter of ἔμβρυος, lit, growing in, from ἐν, in and βρύω, swell, be full, the proper Latinized form of the Greek term would be embryum. In animals, the development of the zygote into an embryo proceeds through specific stages of blastula, gastrula. The blastula stage typically features a fluid-filled cavity, the blastocoel, surrounded by a sphere or sheet of cells, in a placental mammal, an ovum is fertilized in a fallopian tube through which it travels into the uterus. An embryo is called a fetus at an advanced stage of development. In humans, this is from the week of gestation. During gastrulation the cells of the blastula undergo coordinated processes of cell division, invasion, in triploblastic organisms, the three germ layers are called endoderm, ectoderm, and mesoderm. The position and arrangement of the layers are highly species-specific, however. For example, in neurogenesis, a subpopulation of cells is set aside to become the brain, spinal cord. Modern developmental biology is extensively probing the molecular basis for every type of organogenesis, including angiogenesis, chondrogenesis, myogenesis, osteogenesis, and many others. In botany, a plant embryo is part of a seed, consisting of precursor tissues for the leaves, stem. Once the embryo begins to germinate — grow out from the seed — it is called a seedling, bryophytes and ferns also produce an embryo, but do not produce seeds. In these plants, the embryo begins its existence attached to the inside of the archegonium on a parental gametophyte from which the egg cell was generated, the structure and development of the rest of the embryo varies by group of plants. Once the embryo has expanded beyond the enclosing archegonium, it is no longer termed an embryo, embryos are used in various fields of research and in techniques of assisted reproductive technology. An egg may be fertilized in vitro and the embryo may be frozen for later use
10.
Egg cell
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The egg cell, or ovum, is the female reproductive cell in oogamous organisms. The egg cell is not capable of active movement. When egg and sperm fuse, a cell is formed. Karl Ernst von Baer discovered the mammalian ovum in 1827, the fusion of spermatozoa with ova was observed by Oskar Hertwig in 1876. In animals, egg cells are known as ova. The term ovule is used for the young ovum of an animal, in vertebrates, ova are produced by female gonads called ovaries a number of ova are present at birth in mammals and mature via oogenesis. White et al. disproved the longstanding dogma that all of the ova are produced before birth, the team from the Vincent Center for Reproductive Biology, Massachusetts, Boston could prove that oocyte fromation takes place in ovaries of reproductive-age women. This report challenged a fundamental belief, held since the 1950s, in all mammals the ovum is fertilized inside the female body. The human ova grow from primitive germ cells that are embedded in the substance of the ovaries, each of them divides repeatedly to give secretions of the uterine glands, ultimately forming a blastocyst. The ovum is one of the largest cells in the human body, the human ovum measures approximately 0.12 mm in diameter. Ooplasm is the yolk of the ovum, a substance at its center, which contains its nucleus, named the germinal vesicle. Mammalian ova contain only an amount of the nutritive yolk. In contrast, bird eggs contain enough to supply the chick with nutriment throughout the period of incubation. In the oviparous animals the ova develop protective layers and pass through the oviduct to the outside of the body and they are fertilized by male sperm either inside the female body, or outside. After fertilization, an embryo develops, nourished by nutrients contained in the egg and it then hatches from the egg, outside the mothers body. See egg for a discussion of eggs of oviparous animals, the egg cells cytoplasm and mitochondria are the sole means the egg is able to reproduce by mitosis and eventually form a blastocyst after fertilization. Some fish, reptiles and many use this technique. Nearly all land plants have alternating diploid and haploid generations, gametes are produced by the gametophyte, which is the haploid generation
11.
Arthropod
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An arthropod is an invertebrate animal having an exoskeleton, a segmented body, and jointed appendages. Arthropods form the phylum Arthropoda, which includes the insects, arachnids, myriapods, arthropods are characterized by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages, the rigid cuticle inhibits growth, so arthropods replace it periodically by moulting. Their versatility has enabled them to become the most species-rich members of all guilds in most environments. They have over a million described species, making up more than 80% of all described living species, some of which. Arthropods range in size from the microscopic crustacean Stygotantulus up to the Japanese spider crab, arthropods primary internal cavity is a hemocoel, which accommodates their internal organs, and through which their haemolymph – analogue of blood – circulates, they have open circulatory systems. Like their exteriors, the organs of arthropods are generally built of repeated segments. Their nervous system is ladder-like, with paired ventral nerve cords running through all segments and their heads are formed by fusion of varying numbers of segments, and their brains are formed by fusion of the ganglia of these segments and encircle the esophagus. The respiratory and excretory systems of arthropods vary, depending as much on their environment as on the subphylum to which they belong, arthropods also have a wide range of chemical and mechanical sensors, mostly based on modifications of the many setae that project through their cuticles. Aquatic species use internal or external fertilization. Almost all arthropods lay eggs, but scorpions give birth to live young after the eggs have hatched inside the mother, arthropod hatchlings vary from miniature adults to grubs and caterpillars that lack jointed limbs and eventually undergo a total metamorphosis to produce the adult form. The level of care for hatchlings varies from nonexistent to the prolonged care provided by scorpions. The evolutionary ancestry of arthropods dates back to the Cambrian period, the group is generally regarded as monophyletic, and many analyses support the placement of arthropods with cycloneuralians in a superphylum Ecdysozoa. Overall however, the relationships of Metazoa are not yet well resolved. Likewise, the relationships between various groups are still actively debated. Arthropods contribute to the food supply both directly as food, and more importantly indirectly as pollinators of crops. Some species are known to spread disease to humans, livestock. The word arthropod comes from the Greek ἄρθρον árthron, joint, and πούς pous, i. e. foot or leg, arthropods are invertebrates with segmented bodies and jointed limbs
12.
Vertebrate
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Vertebrates /ˈvɜːrtᵻbrᵻts/ comprise all species of animals within the subphylum Vertebrata /-ɑː/. Vertebrates represent the majority of the phylum Chordata, with currently about 66,000 species described. Vertebrates include the fish and the jawed vertebrates, which include the cartilaginous fish. A bony fish known as the lobe-finned fishes is included with tetrapods, which are further divided into amphibians, reptiles, mammals. Extant vertebrates range in size from the frog species Paedophryne amauensis, at as little as 7.7 mm, to the blue whale, vertebrates make up less than five percent of all described animal species, the rest are invertebrates, which lack vertebral columns. The vertebrates traditionally include the hagfish, which do not have proper vertebrae due to their loss in evolution, though their closest living relatives, hagfish do, however, possess a cranium. For this reason, the vertebrate subphylum is sometimes referred to as Craniata when discussing morphology, molecular analysis since 1992 has suggested that hagfish are most closely related to lampreys, and so also are vertebrates in a monophyletic sense. Others consider them a group of vertebrates in the common taxon of craniata. The word origin of vertebrate derives from the Latin word vertebratus, the Proto-Indo-European language origins are still unclear. Vertebrate is derived from the vertebra, which refers to any of the bones or segments of the spinal column. All vertebrates are built along the basic body plan, a stiff rod running through the length of the animal, with a hollow tube of nervous tissue above it. In all vertebrates, the mouth is found at, or right below, the remaining part of the body continuing after the anus forms a tail with vertebrae and spinal cord, but no gut. However, a few vertebrates have secondarily lost this anatomy, retaining the notochord into adulthood, such as the sturgeon, jawed vertebrates are typified by paired appendages, but this trait is not required in order for an animal to be a vertebrate. All basal vertebrates breathe with gills, the gills are carried right behind the head, bordering the posterior margins of a series of openings from the pharynx to the exterior. Each gill is supported by a cartilagenous or bony gill arch, the bony fish have three pairs of arches, cartilaginous fish have five to seven pairs, while the primitive jawless fish have seven. The vertebrate ancestor no doubt had more arches than this, as some of their relatives have more than 50 pairs of gills. In amphibians and some primitive fishes, the larvae bear external gills. These are reduced in adulthood, their function taken over by the gills proper in fishes, some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of tetrapods
13.
Mollusca
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The molluscs compose the large phylum Mollusca of invertebrate animals. Around 85,000 extant species of molluscs are recognized, molluscs are the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats and they are highly diverse, not just in size and in anatomical structure, but also in behaviour and in habitat. The phylum is divided into 9 or 10 taxonomic classes. The gastropods are by far the most numerous molluscs in terms of classified species, the three most universal features defining modern molluscs are a mantle with a significant cavity used for breathing and excretion, the presence of a radula, and the structure of the nervous system. Other than these things, molluscs express great morphological diversity, so many textbooks base their descriptions on an ancestral mollusc. This has a single, limpet-like shell on top, which is made of proteins and chitin reinforced with calcium carbonate, the underside of the animal consists of a single muscular foot. Although molluscs are coelomates, the coelom tends to be small, the main body cavity is a hemocoel through which blood circulates, their circulatory systems are mainly open. The generalized mollusc has two paired nerve cords, or three in bivalves, the brain, in species that have one, encircles the esophagus. Most molluscs have eyes, and all have sensors to detect chemicals, vibrations, the simplest type of molluscan reproductive system relies on external fertilization, but more complex variations occur. All produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, good evidence exists for the appearance of gastropods, cephalopods and bivalves in the Cambrian period 541 to 485.4 million years ago. Molluscs have, for centuries, also been the source of important luxury goods, notably pearls, mother of pearl, Tyrian purple dye and their shells have also been used as money in some preindustrial societies. Mollusc species can also represent hazards or pests for human activities, the bite of the blue-ringed octopus is often fatal, and that of Octopus apollyon causes inflammation that can last for over a month. Stings from a few species of large tropical cone shells can also kill, schistosomiasis is transmitted to humans via water snail hosts, and affects about 200 million people. Snails and slugs can also be serious pests, and accidental or deliberate introduction of some snail species into new environments has seriously damaged some ecosystems. The words mollusc and mollusk are both derived from the French mollusque, which originated from the Latin molluscus, from mollis, molluscus was itself an adaptation of Aristotles τα μαλακά, the soft things, which he applied to cuttlefish. The scientific study of molluscs is accordingly called malacology, as it is now known these groups have no relation to molluscs, and very little to one another, the name Molluscoida has been abandoned. The most universal features of the structure of molluscs are a mantle with a significant cavity used for breathing and excretion
14.
Scorpion
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Scorpions are predatory arachnids of the order Scorpiones. Scorpions range in size from 9 mm /0.3 in. to 23 cm /9 in, the evolutionary history of scorpions goes back to the Silurian era 430 million years ago. They have adapted to a range of environmental conditions and can now be found on all continents except Antarctica. Scorpions number about 1750 described species, with 13 extant families recognised to date, only about 25 of these species are known to have venom capable of killing a human being. The taxonomy has undergone changes and is likely to change further, Scorpion stings are painful but are usually harmless to humans. For stings from species found in North America, no treatment is normally needed for healthy adults, although care should be sought for children. More harmful stings from species found in South America, Africa, Scorpions are found on all major land masses except Antarctica. The greatest diversity of scorpions in the Northern Hemisphere is to be found in the areas lying between latitudes 23° N and 38° N. Above these latitudes, the diversity decreases, with the northernmost natural occurrence of scorpions being the northern scorpion Paruroctonus boreus at Medicine Hat, Alberta, five colonies of scorpions have established themselves in Sheerness on the Isle of Sheppey in the United Kingdom. This small population has been resident since the 1860s, having arrived with imported fruit from Africa. This scorpion species is small and completely harmless to humans, at just over 51° N, this marks the northernmost limit where scorpions live in the wild. There are thirteen families and about 1,750 described species and subspecies of scorpions, in addition, there are 111 described taxa of extinct scorpions. This classification is based on that of Soleglad & Fet, which replaced the older, additional taxonomic changes are from papers by Soleglad et al. The following classification covers extant taxa to the rank of family, L. Koch,1837 Family Buthidae C. L. The oldest known scorpions lived around 430 million years ago in the Silurian period and these first scorpions were believed to have had gills instead of the present forms book lungs though this has subsequently been refuted. The oldest Gondwanan scorpiones comprise the earliest known terrestrial animals from Gondwana, currently,111 fossil species of scorpion are known. Unusually for arachnids, there are species of Palaeozoic scorpion than Mesozoic or Cenozoic ones. The eurypterids, marine creatures that lived during the Palaeozoic era, share several traits with scorpions
15.
Theria
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Theria is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians and the metatherians, therian mammals give birth to live young without using a shelled egg. It is possible thanks to key proteins called syncytins, which allow exchanges between the mother and its offspring through a placenta even rudimental such as the marsupial ones, genetic studies have enlighted the viral origin of syncytins through endogenization process. Therian mammals no longer have the coracoid bone, contrary to their cousins monotremes, pinnae are also a distinctive trait that is a therian exclusivity. The earliest known therian mammal fossil is Juramaia, from the Middle Jurassic of China, however, molecular data suggests that therians may have originated even earlier, during the Early Jurassic. The rank of Theria may vary depending on the system used. The textbook classification system by Vaughan et al. gives the following, marsupials Monotremes Placental mammals Theria — supercohort — Tree of Life
16.
Bird egg
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Bird eggs are laid by the females and incubated for a time that varies according to the species, a single young hatches from each egg. Average clutch sizes range from one to about 17, clutch size may vary latitudinally within a species. Some birds lay eggs even when the eggs have not been fertilized, it is not uncommon for pet owners to find their lone bird nesting on a clutch of infertile eggs, which are sometimes called wind-eggs. The default color of vertebrate eggs is the white of the calcium carbonate from which the shells are made, the pigments biliverdin and its zinc chelate give a green or blue ground color, and protoporphyrin produces reds and browns as a ground color or as spotting. However, the markings on passerine eggs have been suggested to reduce brittleness by acting as a solid state lubricant. If insufficient calcium is available in the soil, the egg shell may be thin. Protoporphyrin speckling compensates for this, and increases inversely to the amount of calcium in the soil, for the same reason, later eggs in a clutch are more spotted than early ones, as the females store of calcium is depleted. Birds which build in trees generally have blue or greenish eggs, either spotted or unspotted, while birds that build in bushes or near or on the ground are likely to lay speckled eggs. For example, Cormorant eggs are rough and chalky Tinamou eggs are shiny Duck eggs are oily, the domestic hens egg has around 7500 pores. The shape of eggs varies considerably across bird species, ranging from near-spherical to highly pyriform or conical with the shape of the chicken egg lying in between. Early scientific investigators of egg shape suggested that the shape of eggs was caused by the egg being forced through the oviduct by peristalsis. The calcification of the egg in the shell gland/uterus then fixes it in shape. These observations cannot be explained by peristalsis and it has been proposed that the egg acquires its shape as it is forced through the narrow isthmus, but this assertion has not been thoroughly verified. Cliff-nesting birds often have highly conical eggs and they are less likely to roll off, tending instead to roll around in a tight circle, this trait is likely to have arisen due to evolution via natural selection. In contrast, many hole-nesting birds have nearly spherical eggs, a pointed egg will tend to sit on its side, with the big end tipped upward. The big end contains the air sac and its shell is pierced by a density of pores than the more pointed end. Tipping the big end upwards improves oxygen flow to the head, with the physiologically demanding eyes and brain. Egg size tends to be proportional to the size of the adult bird, kiwis have disproportionately large eggs, up to 20% of the females body weight
17.
Monotreme
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Monotremes are basal mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals. The only surviving examples of monotremes are all indigenous to Australia and New Guinea, the existing monotreme species are the platypus and four species of echidnas. There is currently debate regarding monotreme taxonomy. The word monotreme comes from the Greek μονός, monos and τρῆμα, trema, in common with reptiles and marsupials, monotremes lack the connective structure which in placental mammals is the primary communication route between the right and left brain hemispheres. Extant monotremes lack teeth as adults, fossil forms and modern platypus young have a tribosphenic form of molars, which is one of the hallmarks of extant mammals. Some recent work suggests that monotremes acquired this form of molar independently of placental mammals and marsupials, toothloss in modern monotremes might be related to their development of electrolocation. Monotreme jaws are constructed differently from those of other mammals. Nonetheless, findings on the extinct species Teinolophos confirm that suspended ear bones evolved independently among monotremes, the external opening of the ear still lies at the base of the jaw. DNA suggests that while this trait is shared and is synapomorphic with birds, platypuses are still mammals, l-ascorbic acid is synthesized only in the kidneys. The monotremes also have extra bones in the girdle, including an interclavicle and coracoid. Monotremes retain a reptile-like gait, with legs on the sides of, rather than underneath, the monotreme leg bears a spur in the ankle region, the spur is not functional in echidnas, but contains a powerful venom in the male platypus. This venom is derived from b-defensins, proteins that are present in mammals that create holes in viral and bacterial pathogens, some reptile venom is also composed of different types of b-defensins, another trait shared with reptiles. It is thought to be an ancient mammalian characteristic, as many non-monotreme archaic mammal groups also possess venomous spurs, the penis only carries semen, urine is excreted through the cloaca. The monotreme penis is similar to a penis, and is covered by a preputial sac. However, the egg is retained for some time within the mother, which provides the egg with nutrients. Newborn monotremes are larval and fetus-like, much like those of marsupials, Monotremes, like all mammals, lactate, but have no defined nipples, excreting the milk from their mammary glands via openings in their skin. All species are long-lived, with low rates of reproduction and relatively prolonged parental care of infants, the zygotes of monotremes, however, undergo meroblastic division, which causes the ovum to split but not completely. Monotremes metabolic rate is low by mammalian standards
18.
Eggshell
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An eggshell is the outer covering of a hard-shelled egg and of some forms of eggs with soft outer coats. Bird eggshells contain calcium carbonate and dissolve in acids, including the vinegar used in cooking. While dissolving, the carbonate in an eggshell reacts with the acid to form carbon dioxide. Insects and other arthropods lay a variety of styles and shapes of eggs, some have gelatinous or skin-like coverings, others have hard eggshells. It may be fibrous or quite liquid, some arthropod eggs do not actually have shells, rather, their outer covering is actually the outermost embryonic membrane, the choroid, which serves to proteact inner layers. The choroid itself can be a structure, and it may have different layers within it. It may have an outermost layer called an exochorion, eggs which must survive in dry conditions usually have hard eggshells, made mostly of dehydrated or mineralized proteins with pore systems to allow respiration. Arthropod eggs can have extensive ornamentation on their outer surfaces, fish and amphibians generally lay eggs which are surrounded by the extraembryonic membranes but do not develop a shell, hard or soft, around these membranes. Some fish and amphibian eggs have thick, leathery coats, especially if they must withstand physical force or desiccation and these type of eggs can also be very small and fragile. While many reptiles lay eggs with flexible, calcified, eggshells, eggs laid by snakes generally have leathery shells which often adhere to one another. Depending on the species, turtles and tortoises lay hard or soft eggs, several species lay eggs which are nearly indistinguishable from bird eggs. The bird egg is a fertilized gamete located on the surface and surrounded by albumen. The albumen in turn is surrounded by two membranes and then the eggshell. The chicken eggshell is 95-97% calcium carbonate crystals, which are stabilized by a protein matrix, without the protein, the crystal structure would be too brittle to keep its form and the organic matrix is thought to have a role in deposition of calcium during the mineralization process. Eggshell formation requires gram amounts of calcium being deposited within hours, the fibrous chicken shell membranes are added in the proximal isthmus of the oviduct. In the distal isthmus mammillae or mammillary knobs are deposited on the surface of the membrane in a regular array pattern. The mammillae are proteoglycan-rich and are thought to control calcification, in the shell gland, mineralization starts at the mammillae. The shell gland fluid contains very high levels of calcium and hydrogen carbonate, the thick calcified layer of the eggshell forms in columns from the mammillae structures, and is known as the palisade layer
19.
Egg tooth
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In some egg-laying animals, the egg tooth is a small, sharp, cranial protuberance used by offspring to break or tear through the eggs surface during hatching. It is present in most reptiles, and similar structures exist in monotremes, Eleutherodactyl frogs, some lizards develop a true tooth that is shed after use, other reptiles and birds generally develop an analogous epidermal horn that is reabsorbed or falls off. A mother bird delivers her young encased in an eggshell, a protective covering consisting of calcium carbonate. The shell protects the chick until it is ready to survive in the outside world, the chick breaks open the shell when it is strong enough and ready. Since the beak and the claws of the bird are not fully developed and cannot penetrate the eggshell and it is only found in emerging chicks and lost soon after hatching, after it is used to penetrate the hard shell that once protected the embryo. In birds, the process of breaking open the eggshell is commonly referred to as pipping, chicks have a pipping muscle on the back of their necks. It is this muscle which gives them the strength to force the egg tooth through the membrane of the eggshell. When a chick becomes too large to absorb oxygen through the pores of its eggshell and this sac provides a few hours worth of air, during which the chick breaks through the eggshell to the outside. The egg tooth falls off several days after hatching, kiwis lack an egg tooth, instead using their legs and beak to break through a relatively thin eggshell. The superprecocial megapodes possess an egg tooth in their embryonic development. Baby snakes generally hatch from eggs with tough, leathery shells, a baby snakes egg tooth tears a hole directly through the shell, and falls off the first time the snake sheds its skin. A baby crocodile has an egg tooth on the end of its snout and it is a tough piece of skin which is resorbed less than two months after hatching. Crocodile eggs are similar to those of birds in that they have an inner membrane, the egg tooth is used to tear open the inner membrane, the baby crocodile can then push its way through the outer shell. If conditions are particularly dry that year, the membrane may be too tough for the crocodile to break through. Generally, however, the crocodile is there to help free it
20.
Whale shark
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The whale shark is a slow-moving filter-feeding carpet shark and the largest known extant fish species. The largest confirmed individual had a length of 12.65 m, unconfirmed claims of considerably larger individuals, over 14 m long and weighing at least 30 t, are not uncommon. The whale shark holds many records for size in the animal kingdom. It is the member of the genus Rhincodon and the only extant member of the family Rhincodontidae. The species originated about 60 million years ago, the whale shark is found in open waters of the tropical oceans and is rarely found in water below 22 °C. Modeling suggests a lifespan of about 70 years, but measurements have proven difficult, Whale sharks have very large mouths and are filter feeders, which is a feeding mode that occurs in only two other sharks, the megamouth shark and the basking shark. They feed almost exclusively on plankton and are not known to pose a threat to humans, the species was distinguished in April 1828 after the harpooning of a 4.6 m specimen in Table Bay, South Africa. Andrew Smith, a military doctor associated with British troops stationed in Cape Town, the name whale shark directly refers to the fishs size, being as large as some species of whales and also that it is a filter feeder like baleen whales. The whale shark inhabits all tropical and warm-temperate seas, the fish is primarily pelagic, living in the open sea but not in the greater depths of the ocean, although it is known to occasionally dive to depths of as much as 1,800 metres. Although typically seen offshore, it has been closer to land, entering lagoons or coral atolls. Its range is restricted to about 30° latitude. It is capable of diving to depths of at least 1,286 m, on 7 February 2012, a large whale shark was found floating 150 kilometres off the coast of Karachi, Pakistan. The length of the specimen was said to be between 11 and 12 m, with a weight of around 15,000 kg, in 2011, more than 400 whale sharks gathered off the Yucatan Coast. It was one of the largest gatherings of whale sharks recorded, aggregations in that area are among the most reliable seasonal gatherings known for whale sharks, with large numbers occurring in most years between May and September. Associated ecotourism has grown rapidly to unsustainable levels, Whale sharks have a mouth that can be 1.5 m wide, containing 300 to 350 rows of tiny teeth and 10 filter pads which it uses to filter feed. Whale sharks have five pairs of gills. The head is wide and flat with two eyes at the front. Whale sharks are grey with a white belly and their skin is marked with pale yellow spots and stripes which are unique to each individual
21.
Common ostrich
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The ostrich or common ostrich is either one or two species of large flightless birds native to Africa, the only living member of the genus Struthio, which is in the ratite family. In 2014, the Somali ostrich was recognized as a distinct species, the common ostrich shares the order Struthioniformes with the kiwis, emus, rheas, and cassowaries. However, phylogenetic studies have shown that it is the group to all other members of Palaeognathae. It is distinctive in its appearance, with a neck and legs, and can run at up to about 70 km/h. The common ostrich is the largest living species of bird and lays the largest eggs of any living bird, the common ostrichs diet consists mainly of plant matter, though it also eats invertebrates. It lives in groups of 5 to 50 birds. When threatened, the ostrich will either hide itself by lying flat against the ground, if cornered, it can attack with a kick of its powerful legs. Mating patterns differ by region, but territorial males fight for a harem of two to seven females. The common ostrich is farmed around the world, particularly for its feathers and its skin is used for leather products and its meat is marketed commercially, with its leanness a common marketing point. Common ostriches usually weigh from 63 to 145 kilograms, or as much as two adult humans, ostriches of the East African race averaged 115 kg in males and 100 kg in females, while the nominate subspecies was found to average 111 kg in unsexed adults. Exceptional male ostriches can weigh up to 156.8 kg, at sexual maturity, male common ostriches can be from 2.1 to 2.8 m in height, while female common ostriches range from 1.7 to 2.0 m tall. New chicks are fawn in colour, with brown spots. During the first year of life, chicks grow at about 25 cm per month, at one year of age, common ostriches weigh approximately 45 kilograms. Their lifespan is up to 40–45 years, the feathers of adult males are mostly black, with white primaries and a white tail. However, the tail of one subspecies is buff, females and young males are greyish-brown and white. The head and neck of both male and female ostriches is nearly bare, with a layer of down. The skin of the neck and thighs is pinkish gray. The eyes are shaded from sunlight from above, However, the head and bill are relatively small for the birds huge size, with the bill measuring 12 to 14.3 cm
22.
Elephant bird
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Elephant birds are members of the extinct family Aepyornithidae. Elephant birds were large to enormous flightless birds that lived on the island of Madagascar. They became extinct, by the 17th or 18th century if not earlier, for reasons that are unclear, Elephant birds comprised the genera Mullerornis and Aepyornis. Aepyornis was among the heaviest of birds, the elephant birds, which were giant ratites native to Madagascar, have been extinct since at least the 17th century. Étienne de Flacourt, a French governor of Madagascar in the 1640s and 1650s, mentions an ostrich-like bird said to inhabit unpopulated regions. In 1659, Flacourt wrote, vouropatra – a large bird which haunts the Ampatres and lays eggs like the ostriches, marco Polo also mentioned hearing stories of very large birds during his journey to the East during the late 13th century. These accounts are today believed to describe elephant birds, Aepyornis, believed to have been more than 3 m tall and weighing perhaps in the range of 350 to 500 kg, was at the time the worlds largest bird. Only the much older species Dromornis stirtoni from Australia is known to rival it in size among the record and is reported to have shared the same estimated upper weight,500 kg. Remains of Aepyornis adults and eggs have been found, in cases the eggs have a length up to 34 cm. The egg weighed about 10 kg, the egg volume is about 160 times greater than that of a chicken egg. Four species are accepted in the genus Aepyornis today, but the validity of some is disputed, with numerous authors treating them all in just one species. Up to three species are included in Mullerornis. Sightings of eggs of elephant birds by sailors could also have been attributed to a giant raptor from Madagascar. Another might be the perception of ratites retaining neotenic features and thus being mistaken for enormous chicks of a more massive bird. The ancient Malagasy name for the bird is vorompatra, meaning bird of the Ampatres, the Ampatres are today known as the Androy region of southern Madagascar. Like the ostrich, rhea, cassowary, emu, kiwi and extinct moa, Mullerornis and Aepyornis were ratites, they could not fly, because Madagascar and Africa separated before the ratite lineage arose, Aepyornis has been thought to have dispersed and become flightless and gigantic in situ. More recently, it has been deduced from DNA sequence comparisons that the closest living relatives of elephant birds are New Zealand kiwis, Elephant birds are actually part of the mid-Cenozoic Australian ratite radiation, their ancestors flew across the Indian Ocean well after Gondwana broke apart. The existence of possible flying palaeognaths in the Miocene such as Proapteryx further supports the view that ratites did not diversify in response to vicariance, Gondwana broke apart in the Cretaceous and their phylogenetic tree does not match the process of continental drift
23.
Dinosaur
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Dinosaurs are a diverse group of reptiles of the clade Dinosauria that first appeared during the Triassic. Although the exact origin and timing of the evolution of dinosaurs is the subject of active research and they became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago. Their dominance continued through the Jurassic and Cretaceous periods and ended when the Cretaceous–Paleogene extinction event led to the extinction of most dinosaur groups 66 million years ago, until the late 20th century, all groups of dinosaurs were believed to be extinct. As such, birds were the dinosaur lineage to survive the mass extinction event. This article deals primarily with non-avian dinosaurs, Dinosaurs are a varied group of animals from taxonomic, morphological and ecological standpoints. Birds, at over 10,000 living species, are the most diverse group of vertebrates besides perciform fish, using fossil evidence, paleontologists have identified over 500 distinct genera and more than 1,000 different species of non-avian dinosaurs. Dinosaurs are represented on every continent by both extant species and fossil remains, while dinosaurs were ancestrally bipedal, many extinct groups included quadrupedal species, and some were able to shift between these stances. Elaborate display structures such as horns or crests are common to all dinosaur groups, evidence suggests that egg laying and nest building are additional traits shared by all dinosaurs.7 meters and heights of 18 meters and were the largest land animals of all time. Still, the idea that dinosaurs were uniformly gigantic is a misconception based in part on preservation bias, as large. Many dinosaurs were small, Xixianykus, for example, was only about 50 cm long. Through the first half of the 20th century, before birds were recognized to be dinosaurs, most of the community believed dinosaurs to have been sluggish. Most research conducted since the 1970s, however, has indicated that all dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction. The large sizes of some groups, as well as their seemingly monstrous and fantastic nature, have ensured dinosaurs regular appearance in best-selling books and films. Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science, the term is derived from the Greek words δεινός and σαῦρος. Though the taxonomic name has often interpreted as a reference to dinosaurs teeth, claws. Instead, dinosaurs, like many forms of reptile sub-groups, did not exhibit characteristics which were traditionally regarded as reptilian. Under phylogenetic nomenclature, dinosaurs are usually defined as the group consisting of Triceratops, Neornithes, their most recent common ancestor, Birds are now recognized as being the sole surviving lineage of theropod dinosaurs. In traditional taxonomy, birds were considered a class that had evolved from dinosaurs
24.
Bee hummingbird
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The bee hummingbird, zunzuncito or Helena hummingbird is a species of hummingbird regarded as the worlds smallest bird. With a mass around 1. 6–2 g and a length of 5–6 cm, the male has the green pileum and fiery red throat, iridescent gorget with elongated lateral plumes, bluish upper-parts, and the rest of the underparts mostly greyish white. The male is smaller than the female, the female is green above, whitish below, with white tips to the outer tail feathers. Compared to other small hummingbirds, which often have a slender appearance, female bee hummingbirds are bluish green with a pale gray underside. The tips of their feathers have white spots. During the mating season, males have a reddish to pink head, chin, the female lays only two eggs at a time, each about the size of a coffee bean. As the smallest bird in the world, its weight is less than 2 grams or about equal in mass to a United States dime, as its name suggests, it is scarcely larger than a bee. Like all hummingbirds, it is a swift, strong flier, the brilliant, iridescent colors of the bee hummingbirds feathers make the bird seem like a tiny jewel. The iridescence is not always noticeable, but depends on the angle at which a person looks at the bird, the birds slender, pointed bill is adapted for probing deep into flowers. The bee hummingbird feeds mainly on nectar, and an insect or spider, by moving its tongue rapidly in. In the process of feeding, the bird picks up pollen on its bill, when it flies from flower to flower, it transfers the pollen. In this way, it plays an important role in plant reproduction, in one day, the bee hummingbird may visit 1,500 flowers. Using bits of cobwebs, bark, and lichen, the bee hummingbird builds a cup-shaped nest that is only about 2.5 cm in diameter. Nests have been built on single clothespins and she lines the nest with soft plant fibers. In this nest she lays her eggs, which are no bigger than peas and she alone incubates the eggs and raises the young. The bee hummingbird has been reported to visit 15 plant species from 15 different genera, however, in more recent studies, only 10 were found, nine of them were found to be endemic to Cuba. Mellisuga helenae is endemic to the entire Cuban archipelago, including the island of Cuba. It is found mainly in Cubas mogote area and uncommonly in Playa Larga near Zapata swamp, the bee hummingbirds breeding season is from March–June
25.
Invertebrate
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Invertebrates are animals that neither possess nor develop a vertebral column, derived from the notochord. This includes all animals apart from the subphylum Vertebrata, familiar examples of invertebrates include insects, crabs, lobsters and their kin, snails, clams, octopuses and their kin, starfish, sea-urchins and their kin, jellyfish, and worms. The majority of species are invertebrates, one estimate puts the figure at 97%. Many invertebrate taxa have a number and variety of species than the entire subphylum of Vertebrata. Some of the invertebrates, such as the Tunicata and Cephalochordata are more closely related to the vertebrates than to other invertebrates. This makes the term invertebrate paraphyletic and hence almost meaningless for taxonomic purposes, the word invertebrate comes from the form of the Latin word vertebra, which means a joint in general, and sometimes specifically a joint from the spinal column of a vertebrate. In turn the jointed aspect of vertebra derived from the concept of turning, coupled with the prefix in-, meaning not or without. The term invertebrates is not always precise among non-biologists since it does not accurately describe a taxon in the way that Arthropoda. Each of these describes an valid taxon, phylum, subphylum or family. Invertebrata is a term of convenience, not a taxon, it has very little circumscriptional significance except within the Chordata, the Vertebrata as a subphylum comprises such a small proportion of the Metazoa that to speak of the kingdom Animalia in terms of Vertebrata and Invertebrata has limited practicality. That would at least circumscribe the Chordata, however, even the notochord would be a less fundamental criterion than aspects of embryological development and symmetry or perhaps bauplan. The following text reflects earlier scientific understanding of the term and of animals which have constituted it. According to this understanding, invertebrates do not possess a skeleton of bone and they include hugely varied body plans. Many have fluid-filled, hydrostatic skeletons, like jellyfish or worms, others have hard exoskeletons, outer shells like those of insects and crustaceans. The most familiar invertebrates include the Protozoa, Porifera, Coelenterata, Platyhelminthes, Nematoda, Annelida, Echinodermata, Mollusca, Arthropoda include insects, crustaceans and arachnids. By far the largest number of described species are insects. The following table lists the number of described extant species for major invertebrate groups as estimated in the IUCN Red List of Threatened Species,2014.3. The IUCN estimates that 66,178 extant vertebrate species have been described, the trait that is common to all invertebrates is the absence of a vertebral column, this creates a distinction between invertebrates and vertebrates
26.
Kingdom (biology)
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In biology, kingdom is the second highest taxonomic rank below domain. Kingdoms are divided into groups called phyla. Traditionally, textbooks from the United States used a system of six kingdoms while textbooks in Great Britain, India, Australia, Latin America and other countries used five kingdoms. Later two further main ranks were introduced, making the kingdom, phylum or division, class, order, family, genus. In the 1960s a rank was introduced above kingdom, namely domain, prefixes can be added so subkingdom and infrakingdom are the two ranks immediately below kingdom. Superkingdom may be considered as an equivalent of domain or empire or as an independent rank between kingdom and domain or subdomain, in some classification systems the additional rank branch can be inserted between subkingdom and infrakingdom. Taxonomic ranks, including kingdoms, were to be groups of organisms with a common ancestor, based on such RNA studies, Carl Woese thought life could be divided into three large divisions and referred to them as the three primary kingdom model or urkingdom model. In 1990, the domain was proposed for the highest rank. This term represents a synonym for the category of dominion, introduced by Moore in 1974, unlike Moore, Whoese et al. did not suggest a Latin term for this category, which represents a further argument supporting the accurately introduced term dominion. It was also found that the eukaryotes are more related to the Archaea than they are to the Eubacteria. Although the primacy of the Eubacteria-Archaea divide has been questioned, it has been upheld by subsequent research, there is no consensus on how many kingdoms exist in the classification scheme proposed by Woese. In 2004, a article by Simpson and Roger noted that the Protista were a grab-bag for all eukaryotes that are not animals. On this basis, the diagram opposite showed the real kingdoms of the eukaryotes, a classification which followed this approach was produced in 2005 for the International Society of Protistologists, by a committee which worked in collaboration with specialists from many societies. It divided the eukaryotes into the same six supergroups, the published classification deliberately did not use formal taxonomic ranks, including that of kingdom. In this system the multicellular animals are descended from the same ancestor as both the unicellular choanoflagellates and the fungi which form the Opisthokonta, Plants are thought to be more distantly related to animals and fungi. Beyond this, there does not appear to be a consensus, rogozin et al. in 2009 noted that The deep phylogeny of eukaryotes is an extremely difficult and controversial problem. The classification of living things into animals and plants is an ancient one, aristotle classified animal species in his History of Animals, while his pupil Theophrastus wrote a parallel work, the Historia Plantarum, on plants. Carl Linnaeus laid the foundations for biological nomenclature, now regulated by the Nomenclature Codes
27.
Spore
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In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavorable conditions. Spores form part of the cycles of many plants, algae, fungi. Bacterial spores are not part of a sexual cycle but are resistant structures used for survival under unfavourable conditions, spores are usually haploid and unicellular and are produced by meiosis in the sporangium of a diploid sporophyte. Under favourable conditions the spore can develop into a new organism using mitotic division, producing a multicellular gametophyte, two gametes fuse to form a zygote which develops into a new sporophyte. This cycle is known as alternation of generations, the term spore derives from the ancient Greek word σπορά spora, meaning seed, sowing, related to σπόρος sporos, sowing, and σπείρειν speirein, to sow. Spores germinate to give rise to haploid gametophytes, while seeds germinate to give rise to diploid sporophytes, vascular plant spores are always haploid. Vascular plants are either homosporous or heterosporous, plants that are homosporous produce spores of the same size and type. Spores can be classified in several ways, In fungi and fungus-like organisms, spores are often classified by the structure in which meiosis, since fungi are often classified according to their spore-producing structures, these spores are often characteristic of a particular taxon of the fungi. Sporangiospores, spores produced by a sporangium in many such as zygomycetes. Zygospores, spores produced by a zygosporangium, characteristic of zygomycetes, ascospores, spores produced by an ascus, characteristic of ascomycetes. Basidiospores, spores produced by a basidium, characteristic of basidiomycetes, aeciospores, spores produced by an aecium in some fungi such as rusts or smuts. Urediniospores, spores produced by a uredinium in some such as rusts or smuts. Teliospores, spores produced by a telium in some such as rusts or smuts. Oospores, spores produced by an oogonium, characteristic of oomycetes, carpospores, spores produced by a carposporophyte, characteristic of red algae. Tetraspores, spores produced by a tetrasporophyte, characteristic of red algae, chlamydospores, thick-walled resting spores of fungi produced to survive unfavorable conditions. Parasitic fungal spores may be classified into internal spores, which germinate within the host, meiospores, spores produced by meiosis, they are thus haploid, and give rise to a haploid daughter cell or a haploid individual. Examples are the cells of gametophytes of seed plants found in flowers or cones. Microspores, meiospores that give rise to a male gametophyte, megaspores, meiospores that give rise to a female gametophyte
28.
Spermatophyte
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The spermatophytes, also known as phanerogams or phenogamae, comprise those plants that produce seeds, hence the alternative name seed plants. They are a subset of the embryophytes or land plants and these terms distinguished those plants with hidden sexual organs from those with visible sexual organs. In addition to the taxa listed above, the record contains evidence of many extinct taxa of seed plants. The so-called seed ferns were one of the earliest successful groups of land plants, glossopteris was the most prominent tree genus in the ancient southern supercontinent of Gondwana during the Permian period. A whole genome duplication event in the ancestor of seed plants occurred about 319 million years ago and this gave rise to a series of evolutionary changes that resulted in the origin of seed plants. A middle Devonian precursor to seed plants from Belgium has been identified predating the earliest seed plants by about 20 million years, runcaria, small and radially symmetrical, is an integumented megasporangium surrounded by a cupule. The megasporangium bears an unopened distal extension protruding above the mutlilobed integument and it is suspected that the extension was involved in anemophilous pollination. Runcaria sheds new light on the sequence of character acquisition leading to the seed, runcaria has all of the qualities of seed plants except for a solid seed coat and a system to guide the pollen to the seed. Seed-bearing plants were divided into angiosperms, or flowering plants, and gymnosperms, which includes the gnetophytes, cycads, ginkgo. Older morphological studies believed in a relationship between the gnetophytes and the angiosperms, in particular based on vessel elements. However, molecular studies have shown a clade of gymnosperms. For example, one common proposed set of relationships is known as the hypothesis and looks like, However
29.
Seed
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A seed is an embryonic plant enclosed in a protective outer covering. The formation of the seed is part of the process of reproduction in seed plants, Seeds are the product of the ripened ovule, after fertilization by pollen and some growth within the mother plant. The embryo is developed from the zygote and the coat from the integuments of the ovule. Seed plants now dominate biological niches on land, from forests to both in hot and cold climates. The term seed also has a meaning that antedates the above—anything that can be sown, e. g. seed potatoes. In the case of sunflower and corn seeds, what is sown is the seed enclosed in a shell or husk, many structures commonly referred to as seeds are actually dry fruits. Plants producing berries are called baccate, sunflower seeds are sometimes sold commercially while still enclosed within the hard wall of the fruit, which must be split open to reach the seed. Different groups of plants have other modifications, the stone fruits have a hardened fruit layer fused to. Nuts are the one-seeded, hard-shelled fruit of plants with an indehiscent seed. Seeds are produced in several related groups of plants, and their manner of production distinguishes the angiosperms from the gymnosperms, angiosperm seeds are produced in a hard or fleshy structure called a fruit that encloses the seeds, hence the name. Some fruits have layers of hard and fleshy material. In gymnosperms, no special structure develops to enclose the seeds, however, the seeds do become covered by the cone scales as they develop in some species of conifer. Seed production in natural plant populations varies widely from year-to-year in response to weather variables, insects and diseases, over a 20-year period, for example, forests composed of loblolly pine and shortleaf pine produced from 0 to nearly 5 million sound pine seeds per hectare. Over this period, there were six bumper, five poor, and nine good seed crops, right after fertilization, the zygote is mostly inactive, but the primary endosperm divides rapidly to form the endosperm tissue. This tissue becomes the food the young plant will consume until the roots have developed after germination, after fertilization the ovules develop into the seeds. The ovule consists of a number of components, The funicle or seed stalk which attaches the ovule to the placenta and hence ovary or fruit wall, the nucellus, the remnant of the megasporangium and main region of the ovule where the megagametophyte develops. The micropyle, a pore or opening in the apex of the integument of the ovule where the pollen tube usually enters during the process of fertilization. The chalaza, the base of the ovule opposite the micropyle, the shape of the ovules as they develop often affects the final shape of the seeds
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Gametophyte
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A gametophyte is a stage in the life cycle of plants and algae that undergo alternation of generations. It is a multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the phase in the life cycle of plants. It develops sex organs that produce gametes, haploid sex cells that participate in fertilization to form a diploid zygote in which each cell has two sets of chromosomes. Cell division of the results in a new diploid multicellular organism, the second stage in the life cycle known as the sporophyte. In some multicellular green algae, red algae and brown algae sporophytes and gametophytes may be externally indistinguishable, in Ulva the gametes are isogamous, all of one size, shape and general morphology. In land plants, anisogamy is universal, as in animals, female and male gametes are called, respectively, eggs and sperm. Either the sporophyte or the gametophyte may be reduced, in bryophytes, the gametophyte is the most visible stage of the life cycle. The bryophyte gametophyte is longer lived, nutritionally independent, and the sporophytes are typically attached to the gametophytes, when a moss spore germinates it grows to produce a filament of cells. The mature gametophyte of mosses develops into leafy shoots that produce sex organs that produce gametes, eggs develop in archegonia and sperm in antheridia. In some bryophyte groups such as many liverworts of the order Marchantiales, in most ferns, gametophyte is a photosynthetic free living organism called a prothallus. However, in groups, notably the clade that includes Ophioglossaceae and Psilotaceae. Extant lycophytes produce several different types of gametophytes, in the families Lycopodiaceae and Huperziaceae, gametophytes are subterranean and mycotrophic, deriving nutrients from symbiosis with fungi. The gametophytes of Isoetes appear to be similar in respect to those of the extinct Carboniferous giant arborescent clubmosses, Lepidodendron. By contrast, in seed plants, gametophytes develop into multicellular organisms while still enclosed within the sporangium, vascular plants that produce only one type of spore are said to be homosporous. They have exosporic gametophytes—that is, the gametophyte is free-living and develops outside of the spore wall, exosporic gametophytes are normally bisexual, capable of producing both sperm and eggs. In heterosporous vascular plants, the gametophyte develops endosporically, within the spore wall and these gametophytes are unisexual, producing either sperm or eggs but not both. All vascular plants are dominant, and a trend toward smaller
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Class (biology)
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In biological classification, class is, a taxonomic rank. Other well-known ranks in descending order of size are life, domain, kingdom, phylum, order, family, genus, as for the other well-known ranks, there is the option of an immediately lower rank, indicated by the prefix sub-, subclass. A taxonomic unit, a taxon, in that rank, in that case the plural is classes The composition of each class is determined by a taxonomist. Often there is no agreement, with different taxonomists taking different positions. There are no rules that a taxonomist needs to follow in describing a class. For example, dogs are assigned to the phylum Chordata, in the class Mammalia. In botany, classes are now rarely discussed, for some clades, a number of alternative classifications are used. In the first edition of his Systema Naturae, carl Linnaeus divided all three of his kingdoms of Nature into classes. The class was considered the highest level of the hierarchy until George Cuviers embranchements. Cladistics List of animal classes Phylogenetics Systematics Taxonomy
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Agnatha
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Agnatha is a superclass of jawless fish in the phylum Chordata, subphylum Vertebrata, consisting of both present and extinct species. The group excludes all vertebrates with jaws, known as gnathostomes, the agnathans as a whole are paraphyletic, because most extinct agnathans belong to the stem group of gnathostomes. Recent molecular data, both from rRNA and from mtDNA as well as embryological data strongly supports the hypothesis that living agnathans, the oldest fossil agnathans appeared in the Cambrian, and two groups still survive today, the lampreys and the hagfish, comprising about 120 species in total. In addition to the absence of jaws, modern agnathans are characterised by absence of paired fins, lampreys have a light sensitive pineal eye. All living and most extinct Agnatha do not have a stomach or any appendages. Fertilization and development are both external, there is no parental care in the Agnatha class. The Agnatha are ectothermic or cold blooded, with a skeleton. Agnathans are ectothermic, meaning they do not regulate their own body temperature, Agnathan metabolism is slow in cold water, and therefore they do not have to eat very much. They have no stomach, but rather a long gut. Lampreys feed on fish and mammals. They rely on a row of teeth to shred their host. Anticoagulant fluids preventing blood clotting are injected into the host, causing the host to more blood. Hagfish are scavengers, eating mostly dead animals and they also use a sharp set of teeth to break down the animal. The fact that Agnathan teeth are unable to move up and down limits their possible food types, in modern agnathans, the body is covered in skin, with neither dermal or epidermal scales. The skin of hagfish has copious slime glands, the slime constituting their defense mechanism, the slime can sometimes clog up enemy fishes gills, causing them to die. In direct contrast, many extinct agnathans sported extensive exoskeletons composed of either massive, almost all agnathans, including all extant agnathans, have no paired appendages, although most do have a dorsal or a caudal fin. Some fossil agnathans, such as osteostracans and pituriaspids, did have paired fins, mode of fertilization in hagfishes is not known. Development in both groups probably is external, there is no known parental care
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Hagfish
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Hagfish, the class Myxini, are eel-shaped, slime-producing marine fish. They are the known living animals that have a skull. Along with lampreys, hagfish are jawless, they are the group to vertebrates. The classification of hagfish has been controversial, the issue is whether the hagfish is a degenerate type of vertebrate-fish, or represents a stage that precedes the evolution of the vertebral column. The original scheme groups hagfish and lampreys together as cyclostomes, as the oldest surviving class of vertebrates alongside gnathostomes, an alternative scheme proposed that jawed vertebrates are more closely related to lampreys than to hagfish, and introduces the category craniata to group vertebrates near hagfish. Recent DNA evidence has supported the original scheme, Hagfish average about 0.5 m in length. The largest known species is Eptatretus goliath with a recorded at 127 cm, while Myxine kuoi. Hagfish have elongated, eel-like bodies, and paddle-like tails, the skin is naked and covers the body like a loosely fitting sock. They have cartilaginous skulls and tooth-like structures composed of keratin, colors depend on the species, ranging from pink to blue-grey, and black or white spots may be present. Eyes are simple eyespots, not compound eyes that can resolve images, Hagfish have no true fins and have six or eight barbels around the mouth and a single nostril. Instead of vertically articulating jaws like Gnathostomata, they have a pair of horizontally moving structures with tooth-like projections for pulling off food, the mouth of the hagfish has two pairs of horny, comb-shaped teeth on a cartilaginous plate that protracts and retracts. These teeth are used to food and draw it toward the pharynx. Hagfish are long and vermiform, and can exude copious quantities of a milky, the typical species Myxine glutinosa was named for this slime. When captured and held, e. g. by the tail, they secrete the microfibrous slime, which expands into up to 20 litres of sticky, gelatinous material when combined with water. This singular behavior may assist them in extricating themselves from the jaws of predatory fish or from the interior of their own prey, recently, the slime was reported to entrain water in its microfilaments, creating a slow-to-dissipate, viscoelastic substance, rather than a simple gel. It has been proven to impair the function of a predator fishs gills, in this case, the hagfishs mucus would clog up the predators gills, disabling their ability to breathe. The predator would release the hagfish as it focused less on eating and it is because of the mucus that there are very few marine predators that target the hagfish. The other known predators of hagfish are varieties of birds or mammals, free-swimming hagfish also slime when agitated and later clear the mucus off by way of the same travelling-knot behavior
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Larva
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A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a phase of their life cycle. The larvas appearance is very different from the adult form. A larva often has unique structures and organs that do not occur in the adult form and their diet may also be considerably different. Larvae are frequently adapted to separate from adults. For example, some such as tadpoles live almost exclusively in aquatic environments. By living in an environment, larvae may be given shelter from predators. Animals in the stage will consume food to fuel their transition into the adult form. In some species like barnacles, adults are immobile but their larvae are mobile, some larvae are dependent on adults to feed them. In many eusocial Hymenoptera species, the larvae are fed by female workers, in Ropalidia marginata the males are also capable of feeding larvae but they are much less efficient, spending more time and getting less food to the larvae. The larvae of species can become pubescent and do not develop further into the adult form. This is a type of neoteny and it is a misunderstanding that the larval form always reflects the groups evolutionary history. This could be the case, but often the stage has evolved secondarily. In these cases the form may differ more than the adult form from the groups common origin. Within Insects, only Endopterygotes show different types of larvae, several classifications have been suggested by many entomologists, and following classification is based on Antonio Berlese classification in 1913. There are four types of endopterygote larvae types, Apodous larvae - no legs at all and are poorly sclerotized. Based on sclerotization, three forms are recognized. Eucephalous - with well sclerotized head capsule, found in Nematocera, Buprestidae and Cerambycidae families
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Lamprey
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Lampreys are any jawless fish of the order Petromyzontiformes, placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like sucking mouth, the common name lamprey is probably derived from Latin lampetra, which may mean stone licker, though the etymology is uncertain. Currently there are about 38 known extant species of lampreys, parasitic species are the best known, and feed by boring into the flesh of other fish to suck their blood, but only 18 species of lampreys are parasitic. Adults of the species do not feed, they live off reserves acquired as ammocoetes. The lampreys are an ancient lineage of vertebrates, though their exact relationship to hagfishes. Adults superficially resemble eels in that they have scaleless, elongated bodies, lacking paired fins, adult lampreys have large eyes, one nostril on the top of the head, and seven gill pores on each side of the head. The pharynx is subdivided, the part forming a respiratory tube that is isolated from the mouth by a valve called the velum. Near the gills are the eyes, which are developed and buried under skin in the larvae. The eyes complete their development during metamorphosis, and in adults are covered by a thin, instead of true vertebrae, they have a series of cartilaginous structures called arcualia arranged above the notochord. Hagfish, which resemble lampreys, have traditionally considered the sister taxon of the true vertebrates. Studies have shown that lampreys are amongst the most energy-efficient swimmers and their swimming movements generate low-pressure zones around their body, which pull rather than push their bodies through the water. Parasitic lampreys feed on prey as adults by attaching their mouthparts to the animals body, then using their teeth to cut through surface tissues until they reach blood. A study of stomach content of some lampreys have also shown remains of intestines, fins, although attacks on humans do occur, they will generally not attack humans unless starved. Non-parasitic lampreys, which are freshwater species, do not feed as adults, they live off reserves acquired as ammocoetes. Lamprey leukocytes express surface variable lymphocyte receptors generated from somatic recombination of leucine-rich repeat gene segments in a recombination activating gene-independent manner, northern lampreys have the highest number of chromosomes among vertebrates. Pouched lamprey larvae also have a high tolerance for free iron in their bodies. Adult lampreys spawn in rivers and then die, the young larvae, ammocoetes, spend several years in the rivers, where they live burrowed in fine sediment, filter feeding on detritus and microorganisms. Then, ammocoetes undergo a metamorphosis lasting several months, some species do not feed after metamorphosis, while others migrate to the sea or lakes, where they feed on different species of fish and even on marine mammals
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Egg case (Chondrichthyes)
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An egg case or egg capsule, colloquially known as a mermaids purse or devils purse, is a casing that surrounds the fertilized eggs of some sharks, skates, and chimaeras. They are made of collagen protein strands, because they are lightweight, they are commonly washed up by the sea, often found at the strandline, the farthest point of the high tide. The egg cases that wash up on beaches are usually empty, furthermore, egg cases are often found in commercial fishing gears like nets and pots, and on the sea floor during surveys using an ROV. Among the 9 extant orders of sharks, egg-laying is found only in three, The egg cases of sharks have spiral flanges that allow them to be wedged inside crevices or into sand. The bamboo sharks and the zebra shark lay eggs on the bottom, the egg cases are oval and covered with adhesive fibers that serve to secure them to the bottom. Some catsharks and the finback catsharks in the genus Proscyllium are the members of their order that lay eggs. The egg cases of catsharks are purse-shaped with long tendrils at the corners that serve to them to structures on the sea floor. That excludes the four long tendrils found in each corner, which assist in anchorage, egg cases from rays vary in that they have points rather than tendrils. The colours and shapes of egg cases also vary greatly from species to species, egg cases are deposited in pairs on the sea floor, and hatchlings are believed to emerge within 9 months. Gestation can take longer, up to 12 months or more for deep sea catsharks which lay their eggs in very cold water, if an egg case is still moist and has no visible hole, it is probably still occupied. The skates are the rays that are oviparous. Females lay egg cases onto the sea floor after fertilization occurs in utero, while in utero, a protected case forms around the embryo which is called the egg case. Studies have been done where egg cases were removed from females to ensure proper identification in regard to skate species. Egg cases have distinguishable characteristic traits that are unique to that species, the two most distinguishable features on the egg case are the keel and the absence or presence of a fibrous covering. A keel runs laterally along both sides of the edge of the egg case, it is a flexible structure. Keels will also run the length of the horns on some skate species, some egg cases have broad keels while others have narrow keels. Many egg cases are covered with a layer of fiber, some will have a fine layer while others have a thick layer, the big skate is known to be the largest skate in the eastern North Pacific Ocean. Their maximum size has been noted as 244 cm total length, the fresh egg cases of the big skate, like the one shown below, were taken from dead gravid females that were caught in commercial groundfish fisheries
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Viviparity
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Viviparity literally means giving live birth, from the Latin vivus and parere. The term is in use both in zoology and in botany as a term for certain classes of modes of reproduction, the adjective viviparous is derived from viviparity and describes both the various modes of reproduction and the organisms that reproduce in any such mode. In botany vivipary is an alternative form of the term. In botany too, the usage of the term is largely a matter of convenience and preference, five modes of reproduction have been differentiated in animals based on relations between zygote and parents. The five include two nonviviparous modes, ovuliparity, with external fertilisation, and oviparity, with internal fertilisation, in the latter, the female lays zygotes as eggs with a large yolk, this occurs in all birds, most reptiles, and some fishes. Hemotrophic viviparity, nutrients are provided by the female, often some form of placenta. In the frog Gastrotheca ovifera, embryos are fed by the mother through specialized gills, the skink Pseudemoia entrecasteauxii and most mammals exhibit a hemotrophic viviparity. Placental viviparity is arguably the most highly developed form of vivipary, Placental mammals, including humans, are the best-known example, but adaptations in some other animals also have incorporated this principle or close analogies. Other examples include species of scorpions and cockroaches, certain genera of sharks and snakes. Ovoviviparity, a less developed form of animal vivipary, ovoviviparity, occurs in most vipers for instance. However, there are arguments in favour of abandoning the term as obsolete, in at least one species of skink in the large genus Trachylepis, placental transport accounts for nearly all of the provisioning of nutrients to the embryos before birth. In the uterus, the eggs are small, about 1mm in diameter, with very little yolk. The shell membrane is vestigial and transient, its disintegration permits the absorption of nutrients from uterine secretions, the embryo then produces invasive chorionic tissues that grow between the cells of the uterine lining till they can absorb nutrients from maternal blood vessels. As it penetrates the lining, the embryonic tissue grows aggressively till it forms sheets of tissue beneath the uterine epithelium and they eventually strip it away and replace it, making direct contact with maternal capillaries. In several respects, the phenomenon is of importance in theoretical zoology. The authors remark that such an endotheliochorial placenta is fundamentally different from that of any known viviparous reptile, there is no relationship between sex-determining mechanisms and whether a species bears live young or lays eggs. Temperature-dependent sex determination, which function in an aquatic environment, is seen only in terrestrial viviparous reptiles. Viviparous plants produce seeds or embryos that begin to develop before they detach from the parent, similarly, some Crassulaceae, such as Bryophyllum, develop and drop plantlets from notches in their leaves, ready to grow
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Osteichthyes
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Osteichthyes /ˌɒstiːˈɪkθi. iːz/, popularly referred to as the bony fish, is a diverse taxonomic group of fish that have skeletons primarily composed of bone tissue, as opposed to cartilage. The vast majority of fish are members of Osteichthyes, which is a diverse and abundant group consisting of 45 orders. It is the largest class of vertebrates in existence today, the group Osteichthyes is divided into the ray-finned fish and lobe-finned fish. The oldest known fossils of fish are about 420 million years ago. Osteichthyes can be compared to Euteleostomi, in paleontology, the terms are synonymous. However, recently published phylogenetic trees treat the Osteichthyes as a clade, bony fish are characterized by a relatively stable pattern of cranial bones, rooted, medial insertion of mandibular muscle in the lower jaw. The head and pectoral girdles are covered with large dermal bones, the eyeball is supported by a sclerotic ring of four small bones, but this characteristic has been lost or modified in many modern species. The labyrinth in the ear contains large otoliths. The braincase, or neurocranium, is divided into anterior and posterior sections divided by a fissure. Early bony fish had simple lungs which helped them breathe in low-oxygen water, in many bony fish these have evolved into swim bladders, which help the body create a neutral balance between sinking and floating. They do not have fin spines, but instead support the fin with lepidotrichia and they also have an operculum, which helps them breathe without having to swim. Bony fish have no placoid scales, most have smooth and overlapping ganoid, cycloid or ctenoid scales. Traditionally, Osteichthyes is considered a class, recognised on having a swim bladder, under this classification systems, the Osteichthyes are paraphyletic with regard to land vertebrates as the common ancestor of all Osteichthyes includes tetrapods amongst its descendants. The largest subclass, the Actinopterygii are monophyletic, but with the inclusion of the smaller sub-class Sarcopterygii and this has led to an alternative classification, splitting the Osteichthyes into two full classes. Paradoxically, Sarcopterygii is under this scheme monophyletic, as it includes the tetrapods, most bony fish belong to the ray-finned fish. The phylogeny of living bony fishes is shown in the cladogram, for the majority this is their sole or main means of respiration. Lungfish and other species are capable of respiration through lungs or vascularized swim bladders. Other species can respire through their skin, intestines, and/or stomach, Osteichthyes are primitively ectothermic, meaning that their body temperature is dependent on that of the water
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Coelacanth
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They follow the oldest known living lineage of Sarcopterygii, which means they are more closely related to lungfish, reptiles and mammals than to the common ray-finned fishes. They are found along the coastlines of the Indian Ocean and Indonesia, since there are only two species of coelacanth and both are threatened, it is the most endangered order of animals in the world. The West Indian Ocean coelacanth is a endangered species. Coelacanths belong to the subclass Actinistia, a group of lobed-finned fish related to lungfish and certain extinct Devonian fish such as osteolepiforms, porolepiforms, rhizodonts, and Panderichthys. Coelacanths were thought to have become extinct in the Late Cretaceous, around 66 million years ago, however, several recent studies have shown that coelacanth body shapes are much more diverse than previously thought. The word Coelacanth is an adaptation of the Modern Latin Cœlacanthus and it is a common name for the oldest living line of Sarcopterygii, referring to the hollow caudal fin rays of the first fossil specimen described and named by Louis Agassiz in 1839. The genus name Latimeria commemorates Marjorie Courtenay-Latimer who discovered the first specimen in a fish market, the coelacanth, which is related to lungfishes and tetrapods, was believed to have been extinct since the end of the Cretaceous period. More closely related to tetrapods than to the fish, coelacanths were considered transitional species between fish and tetrapods. On 23 December 1938, the first Latimeria specimen was found off the east coast of South Africa, Museum curator Marjorie Courtenay-Latimer discovered the fish among the catch of a local angler, Captain Hendrick Goosen. A Rhodes University ichthyologist, J. L. B, smith, confirmed the fishs importance with a famous cable, MOST IMPORTANT PRESERVE SKELETON AND GILLS = FISH DESCRIBED. Since 1938, Latimeria chalumnae have been found in the Comoros, Kenya, Tanzania, Mozambique, Madagascar, only a photograph of the first specimen of this species was made at a local market by Erdmann and his wife Arnaz Mehta before it was bought by a shopper. The coelacanth has no commercial value apart from being coveted by museums. As a food fish it is almost worthless, as its tissues exude oils that give the flesh a foul flavor, the coelacanths continued survival may be threatened by commercial deep-sea trawling, in which coelacanths are caught as bycatch. Coelacanths are a part of the clade Sarcopterygii, or the lobe-finned fishes, externally, several characteristics distinguish the coelacanth from other lobe-finned fish. They possess a three-lobed caudal fin, also called a fin or a diphycercal tail. A secondary tail extending past the tail separates the upper and lower halves of the coelacanth. Cosmoid scales act as armor to protect the coelacanths exterior. Several internal traits also aid in differentiating coelacanths from other lobe-finned fish, at the back of the skull, the coelacanth possesses a hinge, the intracranial joint, which allows it to open its mouth extremely wide
40.
Ovoviviparity
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Ovoviviparity, ovovivipary, or ovivipary, is a mode of reproduction in animals in which embryos that develop inside eggs remain in the mothers body until they are ready to hatch. This method of reproduction is similar to viviparity, but the embryos have no connection with the mother. In some species, this is supplemented by uterine secretions or other maternal provisioning, the terms ovoviviparity or aplacental viviparity have been deprecated because they encompass several unrelated modes of reproduction. In some species, the developing embryos rely solely on yolk. This is known as yolk-sac viviparity and is regarded as a type of lecithotrophy, other species exhibit matrotrophy, in which the embryo exhausts its yolk supply early in gestation and mother provides additional nutrition. This additional provisioning may be in the form of unfertilized eggs, the first two of these modes were categorized under histotroph viviparity, or aplacental viviparity. The young of amphibians are sometimes born as larvae. This is found in Anguis fragilis, in seahorses, zygotes remain in the males ventral marsupium. In the frog Rhinoderma darwinii, the zygotes develop in the vocal sac, in the frog Rheobatrachus, zygotes develop in the stomach. Some insects, notably tachinid flies, are ovolarviparous, which means that the embryos develop into the first larval stage within the eggs still in the females oviduct. As a result, the larvae hatch more rapidly, sometimes immediately after egg deposition, a similar phenomenon is larviparity, in which larvae hatch before the female delivers them, although this may be mistakenly identified in species with very thin and transparent egg membranes
41.
Amphibian
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Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. They inhabit a variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Thus amphibians typically start out as larvae living in water, the young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a respiratory surface and some small terrestrial salamanders and frogs lack lungs. They are superficially similar to lizards but, along with mammals and birds, reptiles are amniotes, the earliest amphibians evolved in the Devonian period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. They diversified and became dominant during the Carboniferous and Permian periods, over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia. The three modern orders of amphibians are Anura, Urodela, and Apoda, the number of known amphibian species is approximately 7,000, of which nearly 90% are frogs. The smallest amphibian in the world is a frog from New Guinea with a length of just 7.7 mm. The largest living amphibian is the 1.8 m Chinese giant salamander, the study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology. The word amphibian is derived from the Ancient Greek term ἀμφίβιος, the term was initially used as a general adjective for animals that could live on land or in water, including seals and otters. Traditionally, the class Amphibia includes all tetrapod vertebrates that are not amniotes, the numbers of species cited above follows Frost and the total number of known amphibian species is over 7,000, of which nearly 90% are frogs. With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a group without unique defining features apart from shared primitive characteristics. Classification varies according to the phylogeny of the author and whether they use a stem-based or a node-based classification. The phylogeny of Paleozoic amphibians is uncertain, and Lissamphibia may possibly fall within groups, like the Temnospondyli or the Lepospondyli. If the common ancestor of amphibians and amniotes is included in Amphibia, all modern amphibians are included in the subclass Lissamphibia, which is usually considered a clade, a group of species that have evolved from a common ancestor. The three modern orders are Anura, Caudata, and Gymnophiona, although the fossils of several older proto-frogs with primitive characteristics are known, the oldest true frog is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona. It is anatomically similar to modern frogs. The oldest known caecilian is another Early Jurassic species, Eocaecilia micropodia, the earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China
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Tadpole
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A tadpole is the larval stage in the life cycle of an amphibian, particularly that of a frog or toad. They are usually wholly aquatic, though some species have tadpoles that are terrestrial, when first hatched from the egg they have a more or less globular body, a laterally compressed tail and internal or external gills. As they grow they undergo metamorphosis, during which process they grow limbs, develop lungs, most tadpoles are herbivorous and during metamorphosis the mouth and internal organs are rearranged to prepare for an adult carnivorous lifestyle. Having no hard parts, it might be expected that fossil tadpoles would not exist, however, traces of biofilms have been preserved and fossil tadpoles have been found dating back to the Miocene. Tadpoles are eaten in parts of the world and are mentioned in folk tales. The name tadpole is from Middle English taddepol, made up of the elements tadde, toad, similarly, pollywog / polliwog is from Middle English polwygle, made up of the same pol, head, and wiglen, to wiggle. Tadpoles are young amphibians that live in the water, though a few tadpoles are semi-terrestrial and terrestrial. During the tadpole stage of the life cycle, most respire by means of autonomous external or internal gills. They do not usually have arms or legs until the transition to adulthood, as a tadpole matures, it most commonly metamorphosizes by gradually growing limbs and then outwardly absorbing its tail by apoptosis. Lungs develop around the time of leg development, and tadpoles late in development will often be found near the surface of the water, where they breathe air. During the final stages of external metamorphosis, the mouth changes from a small. The intestines shorten to accommodate the new diet, most tadpoles are herbivorous, subsisting on algae and plants. Some species are omnivorous, eating detritus and, when available, tadpoles vary greatly in size, both during their development and between species. For example, in a family, Megophryidae, length of late-stage tadpoles varies between 33 millimetres and 106 millimetres. The tadpoles of Pseudis paradoxa grow to 25 centimetres, the largest of any frog, despite their soft-bodied nature and lack of mineralised hard parts, fossil tadpoles have been recovered from Upper Miocene strata. They are preserved by virtue of biofilms, with more robust structures preserved as a carbon film, in Miocene fossils from Libros, Spain, the brain case is preserved in calcium carbonate, and the nerve cord in calcium phosphate. Other parts of the tadpoles bodies exist as organic remains and bacterial biofilms, tadpole remains with telltale external gills are also known from several of the Labyrinthodont groups. Some tadpoles are used as food, tadpoles of megophryid frog Oreolalax rhodostigmatus are particularly large, more than 10 cm in length, and are collected for human consumption in China
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Reptile
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Reptiles are tetrapod animals in the class Reptilia, comprising todays turtles, crocodilians, snakes, amphisbaenians, lizards, tuatara, and their extinct relatives. The study of these traditional reptile orders, historically combined with that of amphibians, is called herpetology. Because some reptiles are more related to birds than they are to other reptiles. For this reason, many scientists prefer to consider the birds part of Reptilia as well. Some early examples include the lizard-like Hylonomus and Casineria, in addition to the living reptiles, there are many diverse groups that are now extinct, in some cases due to mass extinction events. In particular, the K–Pg extinction wiped out the pterosaurs, plesiosaurs, ornithischians, and sauropods, as well as species of theropods, crocodyliforms. Modern non-avian reptiles inhabit every continent with the exception of Antarctica, several living subgroups are recognized, Testudines, approximately 400 species, Sphenodontia,1 species, Squamata, over 9,600 species, Crocodilia,25 species, and Aves,10,000 species. Reptiles are tetrapod vertebrates, creatures that either have four limbs or, unlike amphibians, reptiles do not have an aquatic larval stage. As amniotes, reptile eggs are surrounded by membranes for protection and transport, many of the viviparous species feed their fetuses through various forms of placenta analogous to those of mammals, with some providing initial care for their hatchlings. In the 18th century, the reptiles were, from the outset of classification, the terms reptile and amphibian were largely interchangeable, reptile being preferred by the French. Josephus Nicolaus Laurenti was the first to use the term Reptilia for an expanded selection of reptiles. Today, the two groups are commonly treated under the same heading as herptiles. He subsequently proposed the names of Sauropsida and Ichthyopsida for the two groups. In 1866, Haeckel demonstrated that vertebrates could be divided based on their strategies, and that reptiles, birds. The terms Sauropsida and Theropsida were used again in 1916 by E. S, Goodrich to distinguish between lizards, birds, and their relatives on the one hand and mammals and their extinct relatives on the other. Goodrich supported this division by the nature of the hearts and blood vessels in each group, according to Goodrich, both lineages evolved from an earlier stem group, Protosauria in which he included some animals today considered reptile-like amphibians, as well as early reptiles. Watson observed that the first two groups diverged very early in history, so he divided Goodrichs Protosauria between them. He also reinterpreted Sauropsida and Theropsida to exclude birds and mammals, thus his Sauropsida included Procolophonia, Eosuchia, Millerosauria, Chelonia, Squamata, Rhynchocephalia, Crocodilia, thecodonts, non-avian dinosaurs, pterosaurs, ichthyosaurs, and sauropterygians
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Mammal
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Mammals are any vertebrates within the class Mammalia, a clade of endothermic amniotes distinguished from reptiles by the possession of a neocortex, hair, three middle ear bones and mammary glands. All female mammals nurse their young with milk, secreted from the mammary glands, Mammals include the largest animals on the planet, the great whales. The basic body type is a quadruped, but some mammals are adapted for life at sea, in the air, in trees. The largest group of mammals, the placentals, have a placenta, Mammals range in size from the 30–40 mm bumblebee bat to the 30-meter blue whale. With the exception of the five species of monotreme, all modern mammals give birth to live young, most mammals, including the six most species-rich orders, belong to the placental group. The largest orders are the rodents, bats and Soricomorpha, the next three biggest orders, depending on the biological classification scheme used, are the Primates, the Cetartiodactyla, and the Carnivora. Living mammals are divided into the Yinotheria and Theriiformes There are around 5450 species of mammal, in some classifications, extant mammals are divided into two subclasses, the Prototheria, that is, the order Monotremata, and the Theria, or the infraclasses Metatheria and Eutheria. The marsupials constitute the group of the Metatheria, and include all living metatherians as well as many extinct ones. Much of the changes reflect the advances of cladistic analysis and molecular genetics, findings from molecular genetics, for example, have prompted adopting new groups, such as the Afrotheria, and abandoning traditional groups, such as the Insectivora. The mammals represent the only living Synapsida, which together with the Sauropsida form the Amniota clade, the early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period, this group diverged from the line that led to todays reptiles. Some mammals are intelligent, with some possessing large brains, self-awareness, Mammals can communicate and vocalize in several different ways, including the production of ultrasound, scent-marking, alarm signals, singing, and echolocation. Mammals can organize themselves into fission-fusion societies, harems, and hierarchies, most mammals are polygynous, but some can be monogamous or polyandrous. They provided, and continue to provide, power for transport and agriculture, as well as commodities such as meat, dairy products, wool. Mammals are hunted or raced for sport, and are used as model organisms in science, Mammals have been depicted in art since Palaeolithic times, and appear in literature, film, mythology, and religion. Defaunation of mammals is primarily driven by anthropogenic factors, such as poaching and habitat destruction, Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is accepted, McKenna & Bell and Wilson & Reader provide useful recent compendiums. Though field work gradually made Simpsons classification outdated, it remains the closest thing to a classification of mammals
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Marsupial
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Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia and the Americas, a distinctive characteristic common to these species is that most of the young are carried in a pouch. Well-known marsupials include kangaroos, wallabies, koalas, possums, opossums, wombats, Tasmanian devils, others include the numbat, the bandicoot, the bettong, the bilby, the quoll, and the quokka. Marsupials represent the clade originating from the last common ancestor of extant metatherians, like other mammals in the Metatheria, they give birth to relatively undeveloped young that often reside with the mother in a pouch, for a certain amount of time. Close to 70% of the 334 extant species occur on the Australian continent, the remaining 100 are found in the Americas — primarily in South America, but thirteen in Central America, and one in North America, north of Mexico. Taxonomically, the two divisions of Marsupialia are, American and Australian marsupials. The order Microbiotheria is found in South America, but is believed to be closely related to Australian marsupials. There are many small species in each group. The term opossum is used to refer to American species, while similar Australian species are properly called possums, again, shrew opossums are more closely related to australidelphians than to true opossums. Order Notoryctemorphia. Marsupials have the characteristics of mammals—e. g. Mammary glands, three middle ear bones, and true hair, there are, however, striking differences as well as a number anatomical features that separate them from Eutherians. In addition to the front pouch, which contains multiple nipples for the protection and sustenance of their young, ossified patellae are absent in most modern marsupials and epipubic bones are present. Marsupials also lack a gross communication between the right and left brain hemispheres, the skull has peculiarities in comparison to higher mammals. In general, the skull is small and tight. Holes are located in the front of the orbit, the cheekbone is enlarged and extends further to the rear. The angular extension of the jaw is bent toward the center. Another feature is the palate which, in contrast to the higher mammals foramina. The teeth differ from that of mammals, so that all taxa except wombats have a different number of incisors in the upper and lower jaws
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Ichthyoplankton
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Ichthyoplankton are the eggs and larvae of fish. They are usually found in the zone of the water column, less than 200 metres deep. Ichthyoplankton are planktonic, meaning they cannot swim effectively under their own power, Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better, Fish larvae are part of the zooplankton that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are eaten by larger animals. Fish can produce high numbers of eggs which are released into the open water column. Fish eggs typically have a diameter of about 1 millimetre, the newly hatched young of oviparous fish are called larvae. They are usually formed, carry a large yolk sac and are very different in appearance from juvenile. The larval period in oviparous fish is relatively short, and larvae grow and change appearance. During this transition larvae must switch from their yolk sac to feeding on zooplankton prey, ichthyoplankton can be a useful indicator of the state and health of an aquatic ecosystem. For instance, most late stage larvae in ichthyoplankton have usually been preyed on, so ichthyoplankton tends to be dominated by eggs and early stage larvae. This means that fish, such as anchovies and sardines, are spawning, ichthyoplankton samples can reflect their spawning output. It is also easier and more cost effective to sample trends in egg. Interest in plankton originated in Britain and Germany in the century when researchers discovered there were microorganisms in the sea. They started describing these microorganisms and testing different net configurations, ichthyoplankton research started in 1864 when the Norwegian government commissioned the marine biologist G. O. Sars to investigate fisheries around the Norwegian coast. Sars found fish eggs, particularly cod eggs, drifting in the water and this established that fish eggs could be pelagic, living in the open water column like other plankton. Research vessels collect ichthyoplankton from the ocean using fine mesh nets, the vessels either tow the nets through the sea or pump sea water onboard and then pass it through the net. Ring net tows involve a nylon mesh net fitted to a circular frame and these have largely been replaced by bongo nets, which provide duplicate samples with their dual-net design
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Spawn (biology)
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Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, to refers to the process of releasing the eggs and sperm. Most aquatic animals, except for aquatic mammals and reptiles, reproduce through the process of spawning, spawn consists of the reproductive cells of many aquatic animals, some of which will become fertilized and produce offspring. The process of spawning typically involves females releasing ova into the water, often in large quantities, fungi, such as mushrooms, are also said to spawn a white, fibrous matter that forms the matrix from which they grow. Marine animals, and particularly fish, commonly reproduce by broadcast spawning. This is a method of reproduction where the female releases many unfertilised eggs into the water. At the same time, a male or many males release a lot of sperm into the water which fertilises some of these eggs, the eggs contain a drop of nutrient oil to sustain the embryo as it develops inside the egg case. The oil also provides buoyancy, so the float and drift with the current. The strategy for survival of broadcast spawning is to disperse the fertilised eggs, there the larvae develop as they consume their fat stores, and eventually hatch from the egg capsule into miniature versions of their parents. To survive, they must then become miniature predators themselves, feeding on plankton, fish eventually encounter others of their own kind, where they form aggregations and learn to school. Internally, the sexes of most marine animals can be determined by looking at the gonads, male lampreys, hagfish and salmon discharge their sperm into the body cavity where it is expelled through pores in the abdomen. Male sharks and rays can pass sperm along a duct into a seminal vesicle, externally, many marine animals, even when spawning, show little sexual dimorphism or little difference in colouration. Where species are dimorphic, such as sharks or guppies, the males often have penis-like intromittent organs in the form of a modified fin, a species is semelparous if its individuals spawn only once in their lifetime, and iteroparous if its individuals spawn more than once. The term semelparity comes from the Latin semel, once, and pario, to beget, while iteroparity comes from itero, to repeat, semelparity is sometimes called big bang reproduction, since the single reproductive event of semelparous organisms is usually large and fatal to the spawners. The classic example of an animal is the Pacific salmon, which lives for many years in the ocean before swimming to the freshwater stream of its birth, spawning. Other spawning animals which are semelparous include mayflies, squid, octopus, smelt, capelin, semelparity is often associated with r-strategists. However, most fish and other spawning animals are iteroparous, when the internal ovaries or egg masses of fish and certain marine animals are ripe for spawning they are called roe. Roe from certain species, such as shrimp, scallop, crab, caviar is a name for the processed, salted roe of non-fertilized sturgeon
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Yolk
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The yolk is the portion of an egg with the primary function to supply food for the development of the animal embryo. Reproductive systems in which the mothers body supplies the embryo directly are said to be matrotrophic, in many species, such as all birds, and most reptiles and insects, the yolk takes the form of a special storage organ constructed in the reproductive tract of the mother. In many other animals, especially small species such as some fishes and invertebrates, the yolk material is not in a special organ. Yolks, being mainly stored food, tend to be very concentrated, the proteins function partly as food in their own right, and partly in controlling the storage and supply of the other nutrients. For example, in some species the amount of yolk in an egg cell affects the developmental processes that follow fertilization. Yolk is not living cell material like protoplasm, but largely passive material, the food material, plus associated control structures, is supplied by the maternal body during the process called oogenesis. Apart from animals, other organisms, like algae, specially in the oogamous, in gymnosperms, the remains of the female gametophyte serve also as food supply, and in flowering plants, the endosperm. In the avian egg, the yolk usually is some shade of yellow in colour and it is spherical and is suspended in the egg white by one or two spiral bands of tissue called the chalazae. The yolk mass, together with the egg cell or ovum properlly are enclosed by the vitelline membrane, whose structure is different from a cell membrane. The yolk is mostly extracellular to the oolemma, being not accumulated inside the cytoplasm of the egg cell, contrary to the claim that the egg cell. After the fertilization, the cleavage of the leads to the formation of the germinal disc. As food, the egg yolk is a major source of vitamins. It contains all of the fat and cholesterol, and nearly half of the protein. If left intact when an egg is fried, the yellow yolk surrounded by a flat blob of egg white creates a distinctive sunny-side up form, mixing the two components together before cooking results in a pale yellow mass, as in omelettes and scrambled eggs. The developing embryo inside the egg uses the yolk as sustenance and it is at times separated from the egg white and used in cooking. It is used in painting as a component of traditional egg-tempera and it is used in the production of egg-yolk agar plate medium, useful in testing for the presence of Clostridium perfringens. Egg yolk contains an antibody called antiglobulin, the antibody transfers from the laying hen to the egg yolk by passive immunity to protect both embryo and hatchling from microorganism invasion. Egg yolk can be used to make such as Advocaat or eggnog
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