1.
Drosophila melanogaster
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Drosophila melanogaster is a species of fly in the family Drosophilidae. The species is generally as the common fruit fly or vinegar fly. It is typically used because it is a species that is easy to care for, has four pairs of chromosomes, breeds quickly. D. melanogaster is a common pest in homes, restaurants, flies belonging to the family Tephritidae are also called fruit flies. This can cause confusion, especially in Australia and South Africa, the D. melanogaster lifespan is about 30 days at 29 °C. The developmental period for D. melanogaster varies with temperature, as with many ectothermic species, the shortest development time,7 days, is achieved at 28 °C. Development times increase at higher temperatures due to heat stress, under ideal conditions, the development time at 25 °C is 8.5 days, at 18 °C it takes 19 days and at 12 °C it takes over 50 days. Under crowded conditions, development time increases, while the emerging flies are smaller, females lay some 400 eggs, about five at a time, into rotting fruit or other suitable material such as decaying mushrooms and sap fluxes. The eggs, which are about 0.5 mm long, the resulting larvae grow for about 4 days while molting twice, at about 24 and 48 h after hatching. During this time, they feed on the microorganisms that decompose the fruit, the mother puts feces on the egg sacs to establish the same microbial composition in the larvaes guts which has worked positively for herself. Then the larvae encapsulate in the puparium and undergo a four-day-long metamorphosis, the female fruit fly prefers a shorter duration when it comes to sex. Males, on the hand, prefer it to last longer. Males perform a sequence of five behavioral patterns to court females, first, males orient themselves while playing a courtship song by horizontally extending and vibrating their wings. Soon after, the positions itself at the rear of the females abdomen in a low posture to tap. Finally, the male curls its abdomen and attempts copulation, females can reject males by moving away, kicking, and extruding their ovipositor. Copulation lasts around 15–20 minutes, during which males transfer a few hundred, females store the sperm in a tubular receptacle and in two mushroom-shaped spermathecae, sperm from multiple matings compete for fertilization. A last male precedence is believed to exist in which the last male to mate with a female sires about 80% of her offspring and this precedence was found to occur through both displacement and incapacitation. The displacement is attributed to sperm handling by the fly as multiple matings are conducted and is most significant during the first 1–2 days after copulation
2.
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
3.
Vertebral column
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The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column houses the spinal canal, a cavity that encloses, there are about 50,000 species of animals that have a vertebral column. The human vertebral column is one of the most-studied examples, the articulating vertebrae are named according to their region of the spine. There are seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae, the number of vertebrae in a region can vary but overall the number remains the same. The number of those in the region however is only rarely changed. There are ligaments extending the length of the column at the front and the back, the vertebrae in the human vertebral column are divided into different regions, which correspond to the curves of the spinal column. The articulating vertebrae are named according to their region of the spine, vertebrae in these regions are essentially alike, with minor variation. These regions are called the spine, thoracic spine, lumbar spine, sacrum. There are seven cervical vertebrae, twelve thoracic vertebrae and five lumbar vertebrae, the number of vertebrae in a region can vary but overall the number remains the same. The number of those in the region however is only rarely changed. The vertebrae of the cervical, thoracic and lumbar spines are independent bones, the vertebrae of the sacrum and coccyx are usually fused and unable to move independently. Two special vertebrae are the atlas and axis, on which the head rests, a typical vertebra consists of two parts, the vertebral body and the vertebral arch. The vertebral arch is posterior, meaning it faces the back of a person, together, these enclose the vertebral foramen, which contains the spinal cord. Because the spinal cord ends in the spine, and the sacrum and coccyx are fused. Two transverse processes and one process are posterior to the vertebral body. The spinous process comes out the back, one transverse process comes out the left, the spinous processes of the cervical and lumbar regions can be felt through the skin. Above and below each vertebra are joints called facet joints and these restrict the range of movement possible, and are joined by a thin portion of the neural arch called the pars interarticularis. In between each pair of vertebrae are two small holes called intervertebral foramina, the spinal nerves leave the spinal cord through these holes
4.
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
5.
Insect
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Insects are a class of hexapod invertebrates within the arthropod phylum that have a chitinous exoskeleton, a three-part body, three pairs of jointed legs, compound eyes and one pair of antennae. They are the most diverse group of animals on the planet, including more than a million described species, the number of extant species is estimated at between six and ten million, and potentially represent over 90% of the differing animal life forms on Earth. Insects may be found in all environments, although only a small number of species reside in the oceans. The life cycles of insects vary but most hatch from eggs, insect growth is constrained by the inelastic exoskeleton and development involves a series of molts. The immature stages can differ from the adults in structure, habit and habitat, Insects that undergo 3-stage metamorphosis lack a pupal stage and adults develop through a series of nymphal stages. The higher level relationship of the Hexapoda is unclear, fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 55 to 70 cm. The most diverse insect groups appear to have coevolved with flowering plants, adult insects typically move about by walking, flying or sometimes swimming. As it allows for rapid yet stable movement, many insects adopt a tripedal gait in which they walk with their legs touching the ground in alternating triangles, Insects are the only invertebrates to have evolved flight. Many insects spend at least part of their lives under water, with adaptations that include gills. Some species, such as water striders, are capable of walking on the surface of water, Insects are mostly solitary, but some, such as certain bees, ants and termites, are social and live in large, well-organized colonies. Some insects, such as earwigs, show maternal care, guarding their eggs, Insects can communicate with each other in a variety of ways. Male moths can sense the pheromones of female moths over great distances, other species communicate with sounds, crickets stridulate, or rub their wings together, to attract a mate and repel other males. Lampyridae in the beetle order communicate with light, humans regard certain insects as pests, and attempt to control them using insecticides and a host of other techniques. Some insects damage crops by feeding on sap, leaves or fruits, a few parasitic species are pathogenic. Some insects perform complex ecological roles, blow-flies, for example, help consume carrion, Many other insects are considered ecologically beneficial as predators and a few provide direct economic benefit. Silkworms and bees have been used extensively by humans for the production of silk and honey, in some cultures, people eat the larvae or adults of certain insects. Insect first appears documented in English in 1601 in Hollands translation of Pliny, translations of Aristotles term also form the usual word for insect in Welsh, Serbo-Croatian, Russian, etc. The evolutionary relationship of insects to other animal groups remains unclear, in the Pancrustacea theory, insects, together with Entognatha, Remipedia, and Cephalocarida, make up a natural clade labeled Miracrustacea
6.
Crustacean
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Crustaceans form a large, diverse arthropod taxon which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill, woodlice and barnacles. In other words, some crustaceans are more related to insects. The 67,000 described species range in size from Stygotantulus stocki at 0.1 mm, to the Japanese spider crab with a leg span of up to 3.8 m, like other arthropods, crustaceans have an exoskeleton, which they moult to grow. Most crustaceans are free-living aquatic animals, but some are terrestrial, some are parasitic, the group has an extensive fossil record, reaching back to the Cambrian, and includes living fossils such as Triops cancriformis, which has existed apparently unchanged since the Triassic period. More than 10 million tons of crustaceans are produced by fishery or farming for human consumption, krill and copepods are not as widely fished, but may be the animals with the greatest biomass on the planet, and form a vital part of the food chain. The scientific study of crustaceans is known as carcinology, and a scientist who works in carcinology is a carcinologist, the body of a crustacean is composed of segments, which are grouped into three regions, the cephalon or head, the thorax, and the pleon or abdomen. The head and thorax may be fused together to form a cephalothorax, the crustacean body is protected by the hard exoskeleton, which must be moulted for the animal to grow. The shell around each somite can be divided into a dorsal tergum, ventral sternum, various parts of the exoskeleton may be fused together. The abdomen bears pleopods, and ends in a telson, which bears the anus, the number and variety of appendages in different crustaceans may be partly responsible for the groups success. It is unclear whether the condition is a derived state which evolved in crustaceans. Trilobites, for instance, also possessed biramous appendages, the main body cavity is an open circulatory system, where blood is pumped into the haemocoel by a heart located near the dorsum. Malacostraca have haemocyanin as the pigment, while copepods, ostracods, barnacles. The alimentary canal consists of a tube that often has a gizzard-like gastric mill for grinding food and a pair of digestive glands that absorb food. Structures that function as kidneys are located near the antennae, a brain exists in the form of ganglia close to the antennae, and a collection of major ganglia is found below the gut. In many decapods, the first pair of pleopods are specialised in the male for sperm transfer, many terrestrial crustaceans mate seasonally and return to the sea to release the eggs. Others, such as woodlice, lay their eggs on land, in most decapods, the females retain the eggs until they hatch into free-swimming larvae. Marine crustaceans are as ubiquitous in the oceans as insects are on land, some branchiurans are able to withstand rapid changes of salinity and will also switch hosts from marine to non-marine species. Krill are the layer and the most important part of the food chain in Antarctic animal communities
7.
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
8.
Echinoderm
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Echinoderm is the common name given to any member of the phylum Echinodermata of marine animals. The adults are recognizable by their symmetry, and include such well-known animals as sea stars, sea urchins, sand dollars. Echinoderms are found at every ocean depth, from the zone to the abyssal zone. The phylum contains about 7000 living species, making it the second-largest grouping of deuterostomes, echinoderms are also the largest phylum that has no freshwater or terrestrial representatives. Aside from the hard-to-classify Arkarua, the first definitive members of the phylum appeared near the start of the Cambrian, the echinoderms are important both ecologically and geologically. Ecologically, there are few other groupings so abundant in the desert of the deep sea. Most echinoderms are able to regenerate tissue, organs, limbs, geologically, the value of echinoderms is in their ossified skeletons, which are major contributors to many limestone formations, and can provide valuable clues as to the geological environment. They were the most used species in regenerative research in the 19th and 20th centuries, further, it is held by some scientists that the radiation of echinoderms was responsible for the Mesozoic Marine Revolution. Along with the chordates and hemichordates, echinoderms are deuterostomes, one of the two divisions of the bilaterians, the other being the protostomes. During the early development of the embryo, in deuterostomes, the blastopore becomes the anus whereas in the protostomes, in deuterostomes, the mouth develops at a later stage, at the opposite end of the blastula from the blastopore, and a gut forms connecting the two. There are a total of about 7,000 extant species of echinoderm as well as about 13,000 extinct species and they are found in habitats ranging from shallow intertidal areas to abyssal depths. These consist of the Crinoidea and the extinct blastoids and Paracrinoids, a fifth class of Eleutherozoa consisting of just three species, the Concentricycloidea, were recently merged into the Asteroidea. The fossil record includes a number of other classes which do not appear to fall into any extant crown group. All echinoderms are marine and nearly all are benthic, the oldest known echinoderm fossil may be Arkarua from the Precambrian of Australia. It is a fossil with radial ridges on the rim. However, no stereom or internal structure showing a water system is present. The first universally accepted echinoderms appear in the Lower Cambrian period, asterozoans appeared in the Ordovician, echinoderms left behind an extensive fossil record. It is hypothesised that the ancestor of all echinoderms was a simple, motile, bilaterally symmetrical animal with a mouth, gut and this ancestral stock adopted an attached mode of life and suspension feeding, and developed radial symmetry as this was more advantageous for such an existence
9.
Jellyfish
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Jellyfish or jellies are softbodied, free-swimming aquatic animals with a gelatinous umbrella-shaped bell and trailing tentacles. The bell can pulsate to acquire propulsion and locomotion, the tentacles may be utilized to capture prey or defend against predators by emitting toxins in a painful sting. Jellyfish species are classified in the subphylum Medusozoa which makes up a part of the phylum Cnidaria. Jellyfish are found in ocean, from the surface to the deep sea. Scyphozoans are exclusively marine, but some live in freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide, Jellyfish have roamed the seas for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal. The popular English name jellyfish has been in use since 1796 and it has traditionally also been applied to other animals sharing a superficial resemblance, for example ctenophores were included as jellyfishes. Even some scientists include the phylum ctenophora when they are referring to jellyfish, other scientists prefer to use the more all-encompassing term gelatinous zooplankton, when referring to these, together with other soft-bodied animals in the water column. As jellyfish are not true fish, which are vertebrates, the jellyfish is considered by some to be a misnomer. Public aquaria often use the terms jellies or sea jellies instead, the term jellies may have become more popular than jellyfish. In scientific literature, jelly and jellyfish are often used interchangeably, some sources may use the term jelly to refer to organisms in this taxon, as jellyfish may be considered inappropriate. Many textbooks and sources refer to only scyphozoans as true jellyfish, a group of jellyfish is sometimes called a bloom or a swarm. Bloom is usually used for a group of jellyfish that gather in a small area. Another collective name for a group of jellyfish is a smack, using swarm usually implies some kind of active ability to stay together, which a few species such as Aurelia, the moon jelly, demonstrate. Medusa jellyfish may be classified as scyphomedusae, stauromedusae, cubomedusae, or hydromedusae, the term medusa was coined by Linnaeus in 1752, alluding to the tentacled head of Medusa in Greek mythology. This term refers exclusively to the non-polyp life-stage which occurs in many cnidarians, all medusa-producing species belong to the sub-phylum Medusozoa. In biology, a medusa is a form of cnidarian in which the body is shaped like an umbrella, medusae vary from bell-shaped to the shape of a thin disk, scarcely convex above and only slightly concave below. The digestive cavity consists of the cavity and radiating canals which extend toward the margin, these canals may be simple or branching
10.
Worm
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Worms /ˈwɜːrm/ are many different distantly related animals that typically have a long cylindrical tube-like body and no limbs. Various types of worm occupy a variety of parasitic niches. Free-living worm species do not live on land, but instead live in marine or freshwater environments, in biology, worm refers to an obsolete taxon, vermes, used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, now seen to be paraphyletic. The name stems from the Old English word wyrm, most animals called worms are invertebrates, but the term is also used for the amphibian caecilians and the slow worm Anguis, a legless burrowing lizard. Invertebrate animals commonly called worms include annelids, nematodes, platyhelminthes, marine worms, marine Chaetognatha, priapulid worms. Worms may also be called helminths, particularly in medical terminology when referring to parasitic worms, when an animal or human is said to have worms, it means that it is infested with parasitic worms, typically roundworms or tapeworms. Lungworm is also a parasitic worm found in various animal species such as fish. Worms can be divided into groups, but are still technically decomposers. The first of these, Platyhelminthes, includes the flatworms, tapeworms and they have a flat, ribbon- or leaf-shaped body with a pair of eyes at the front. The second group contains the threadworms, roundworms, and hookworms, threadworms may be microscopic, such as the vinegar eelworm, or more than 1 metre long. They are found in earth, moss, decaying substances, fresh water. The Guinea worm, for example, gets under the skin of the feet, the third group consists of the segmented worms, with bodies divided into segments, or rings. Among these are the earthworms and the worms of the sea. In earlier taxonomic classification, all the above were included in the now obsolete group Vermes, familiar worms include the earthworms, members of phylum Annelida. Other invertebrate groups may be called worms, especially colloquially, in particular, many unrelated insect larvae are called worms, such as the railroad worm, woodworm, glowworm, bloodworm, inchworm, mealworm, silkworm, and wooly bear worm. Worms may also be called helminths, particularly in medical terminology when referring to parasitic worms, hence helminthology is the study of parasitic worms. When a human or an animal, such as a dog or horse, is said to have worms, it means that it is infested with parasitic worms, deworming is a method to kill off the worms that have infected a human or animal by giving anthelmintic drugs. Ringworm is not a worm at all, but a skin fungus, wurm, or wyrm was the Old English term for carnivorous reptiles, and mythical dragons
11.
Taxon
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In biology, a taxon is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is known by a particular name and given a particular ranking, especially if. It is not uncommon, however, for taxonomists to remain at odds over what belongs to a taxon, if a taxon is given a formal scientific name, its use is then governed by one of the nomenclature codes specifying which scientific name is correct for a particular grouping. Many modern systematists, such as advocates of phylogenetic nomenclature, use cladistic methods that require taxa to be monophyletic and their basic unit, therefore, is the clade rather than the taxon. Similarly, among those contemporary taxonomists working with the traditional Linnean nomenclature, an example of a well-established taxon that is not also a clade is the class Reptilia, the reptiles, birds are descendants of reptiles but are not included in the Reptilia. The term taxon was first used in 1926 by Adolf Meyer-Abich for animal groups, for plants, it was proposed by Herman Johannes Lam in 1948, and it was adopted at the VII International Botanical Congress, held in 1950. The Glossary of the International Code of Zoological Nomenclature defines a taxon, a taxon encompasses all included taxa of lower rank and individual organisms. A taxon can be assigned a rank, usually when it is given a formal name. Phylum applies formally to any domain, but traditionally it was always used for animals, whereas Division was traditionally often used for plants, fungi. A prefix is used to indicate a ranking of lesser importance, the prefix super- indicates a rank above, the prefix sub- indicates a rank below. In zoology the prefix infra- indicates a rank below sub-, for instance, among the additional ranks of class are superclass, subclass and infraclass. Rank is relative, and restricted to a particular systematic schema, for example, liverworts have been grouped, in various systems of classification, as a family, order, class, or division. Many cladists do not see any need to depart from traditional nomenclature as governed by the ICZN, ICN, etc
12.
Tunicate
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A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata, which is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords. The subphylum was at one time called Urochordata, and the term urochordates is still used for these animals. Some tunicates live as solitary individuals, but others replicate by budding and become colonies and they are marine filter feeders with a water-filled, sac-like body structure and two tubular openings, known as siphons, through which they draw in and expel water. During their respiration and feeding, they take in water through the incurrent siphon, various species are commonly known as sea squirts, sea pork, sea livers, or sea tulips. The earliest probable species of tunicate appears in the record in the early Cambrian period. Their name derives from their outer covering or tunic, which is formed from proteins and carbohydrates. In some species, it is thin, translucent, and gelatinous, while in others it is thick, tough, about 2,150 species of tunicate exist in the worlds oceans, living mostly in shallow water. The most numerous group is the ascidians, fewer than 100 species of these are found at greater than 200 m. Some are solitary animals leading a sessile existence attached to the seabed, but others are colonial and a few are pelagic. Some are supported by a stalk, but most are attached directly to a substrate and they are found in a range of solid or translucent colours and may resemble seeds, grapes, peaches, barrels, or bottles. One of the largest is a stalked sea tulip, Pyura pachydermatina, the Tunicata were established by Jean-Baptiste Lamarck in 1816. In 1881, Francis Maitland Balfour introduced a name for the same group, Urochorda. Accordingly, the current trend is to abandon the name Urochorda or Urochordata in favour of the original Tunicata, and it is accepted as valid by the World Register of Marine Species but not by the Integrated Taxonomic Information System. Various common names are used for different species, sea tulips are tunicates with colourful bodies supported on slender stalks. Sea squirts are so named because of their habit of contracting their bodies sharply, sea liver and sea pork get their names from the resemblance of their dead colonies to pieces of meat. Tunicates are more related to craniates, than to lancelets, echinoderms, hemichordates. The clade consisting of tunicates and vertebrates is called Olfactores, although the traditional classification is provisionally accepted, newer evidence suggests the Ascidiacea are an artificial group of paraphyletic status. Undisputed fossils of tunicates are rare, the best known and earliest unequivocally identified species is Shankouclava shankouense from the Lower Cambrian Maotianshan Shale at Shankou village, Anning, near Kunming
13.
Lancelet
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They are the modern representatives of the subphylum Cephalochordata, formerly thought to be the sister group of the craniates. In Asia, they are harvested commercially as food for humans and they are an important object of study in zoology as they provide indications about the evolutionary origins of the vertebrates. Lancelets serve as an intriguing comparison point for tracing how vertebrates have evolved and adapted, although lancelets split from vertebrates more than 520 million years ago, their genomes hold clues about evolution, particularly how vertebrates have employed old genes for new functions. They are regarded as similar to the archetypal vertebrate form, the first representative organism of the group to be described was Branchiostoma lanceolatum. It was described by Peter Simon Pallas in 1774 as molluscan slugs in the genus Limax and it was not until 1834 that Gabriel Costa brought the phylogenetic position of the group closer to the agnathan vertebrates, including it in the new genus Branchiostoma. In 1836, Yarrel renamed the genus as Amphioxus, now considered a synonym of the genus Branchiostoma. Today, the term amphioxus is still used as a name for the Amphioxiformes, along with lancelet. A non-technical review of all aspects of biology is, Stokes, M. D. and Holland. The genome of the Florida lancelet has been sequenced, lancelets are typically 5 centimetres long, or 7 centimetres at the longest. They have a translucent, somewhat fish-like body, but without any paired fins or other limbs, a relatively poorly developed tail fin is present, so they are not especially good swimmers. While they do possess some cartilage-like material stiffening the gill slits, mouth, in common with vertebrates, lancelets have a hollow nerve cord running along the back, pharyngeal slits and a tail that runs past the anus. Also like vertebrates, the muscles are arranged in blocks called myomeres, unlike vertebrates, the dorsal nerve cord is not protected by bone but by a simpler notochord made up of a cylinder of cells that are closely packed to form a toughened rod. The lancelet notochord, unlike the vertebrate spine, extends into the head and this gives the subphylum its name. The nerve cord is only larger in the head region than in the rest of the body. However, developmental gene expression and Transmission electron microscopy indicate the presence of a diencephalic forebrain, a possible midbrain, lancelets have two known kinds of light-sensing structures, Joseph cells, and Hesse organs, as well as a frontal eye and lamellar body. The frontal eye is thought to be light-sensitive, although this has not been confirmed by electrophysiological measurement. The lamellar body, a homologue of the pineal body, was once thought to be light-sensitive. All of these organs and structures are located in the tube, with the frontal eye at the front, followed by the lamellar body, the Joseph cells
14.
Paraphyly
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In taxonomy, a group is paraphyletic if it consists of the groups last common ancestor and all descendants of that ancestor excluding a few—typically only one or two—monophyletic subgroups. The group is said to be paraphyletic with respect to the excluded subgroups, the term is commonly used in phylogenetics and in linguistics. The term was coined to apply to well-known taxa like reptiles which, as commonly named and traditionally defined, is paraphyletic with respect to mammals and birds. Reptilia contains the last common ancestor of reptiles and all descendants of that all extant reptiles as well as the extinct synapsids—except for mammals. Other commonly recognized paraphyletic groups include fish, monkeys and lizards, if many subgroups are missing from the named group, it is said to be polyparaphyletic. A paraphyletic group cannot be a clade, which is a monophyletic group, groups that include all the descendants of a common ancestor are said to be monophyletic. A paraphyletic group is a group from which one or more subsidiary clades is excluded to form a separate group. Ereshefsky has argued that paraphyletic taxa are the result of anagenesis in the group or groups. For example, dinosaurs are paraphyletic with respect to birds because birds possess many features that dinosaurs lack, a group whose identifying features evolved convergently in two or more lineages is polyphyletic. More broadly, any taxon that is not paraphyletic or monophyletic can be called polyphyletic and these terms were developed during the debates of the 1960s and 70s accompanying the rise of cladistics. The prokaryotes, because they exclude the eukaryotes, a descendant group, bacteria and Archaea are prokaryotes, but archaea and eukaryotes share a common ancestor that is not ancestral to the bacteria. The prokaryote/eukaryote distinction was proposed by Edouard Chatton in 1937 and was accepted after being adopted by Roger Stanier. The botanical code abandoned consideration of bacterial nomenclature in 1975, currently, dicotyledons are paraphyletic because the group excludes monocotyledons. Dicotyledon has not been used as an ICBN classification for decades, phylogenetic analysis indicates that the monocots are a development from a dicot ancestor. Excluding monocots from the dicots makes the latter a paraphyletic group, the order Artiodactyla, because it excludes Cetaceans. In the ICZN Code, the two taxa are orders of equal rank, molecular studies, however, have shown that the Cetacea descend from the Artiodactyl ancestors, although the precise phylogeny within the order remains uncertain. Without the Cetacean descendants the Artiodactyls must be paraphyletic, the class Reptilia as traditionally defined, because it excludes birds and mammals. In the ICZN Code, the three taxa are classes of equal rank, however, mammals hail from the synapsids and birds are descended from the dinosaurs, both of which are reptiles
15.
Taxonomy (biology)
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Taxonomy is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. The exact definition of taxonomy varies from source to source, but the core of the remains, the conception, naming. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy, the broadest meaning of taxonomy is used here. The word taxonomy was introduced in 1813 by Candolle, in his Théorie élémentaire de la botanique, the term alpha taxonomy is primarily used today to refer to the discipline of finding, describing, and naming taxa, particularly species. In earlier literature, the term had a different meaning, referring to morphological taxonomy, ideals can, it may be said, never be completely realized. They have, however, a value of acting as permanent stimulants. Some of us please ourselves by thinking we are now groping in a beta taxonomy, turrill thus explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy, thus, Ernst Mayr in 1968 defined beta taxonomy as the classification of ranks higher than species. This activity is what the term denotes, it is also referred to as beta taxonomy. How species should be defined in a group of organisms gives rise to practical and theoretical problems that are referred to as the species problem. The scientific work of deciding how to define species has been called microtaxonomy, by extension, macrotaxonomy is the study of groups at higher taxonomic ranks, from subgenus and above only, than species. While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations, earlier works were primarily descriptive, and focused on plants that were useful in agriculture or medicine. There are a number of stages in scientific thinking. Early taxonomy was based on criteria, the so-called artificial systems. Later came systems based on a complete consideration of the characteristics of taxa, referred to as natural systems, such as those of de Jussieu, de Candolle and Bentham. The publication of Charles Darwins Origin of Species led to new ways of thinking about classification based on evolutionary relationships and this was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler and Engler, the advent of molecular genetics and statistical methodology allowed the creation of the modern era of phylogenetic systems based on cladistics, rather than morphology alone. Taxonomy has been called the worlds oldest profession, and naming and classifying our surroundings has likely been taking place as long as mankind has been able to communicate
16.
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
17.
Pangolin
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Pangolins are mammals of the order Pholidota. These species range in size from 30 to 100 cm, a number of extinct pangolin species are also known. Pangolins have large, protective keratin scales covering their skin, they are the only mammals with this adaptation. They live in trees or burrows, depending on the species. Pangolins are nocturnal, and their diet consists of mainly ants and they tend to be solitary animals, meeting only to mate and produce a litter of one to three offspring which are raised for about two years. Pangolins are threatened by hunting and heavy deforestation of their natural habitats, the name pangolin comes from the Malay word pengguling, meaning something that rolls up. The physical appearance of a pangolin is marked by large, hardened, overlapping scales, which are soft on newborn pangolins. They are made of keratin, the material of which human fingernails. The pangolins scaled body is comparable to a cone or globe artichoke. It can curl up into a ball when threatened, with its overlapping scales acting as armor, the scales are sharp, providing extra defense from predators. Pangolins can also emit a chemical from glands near the anus. They have short legs, with sharp claws which they use for burrowing into termite and ant mounds, large pangolins can extend their tongues as much as 40 cm, with a diameter of only 0.5 cm. Most pangolins are nocturnal animals that use their sense of smell to find insects. The long-tailed pangolin is also active by day, while species of pangolins spend most of the daytime sleeping. Arboreal pangolins live in trees, whereas the ground-dwelling species dig tunnels underground. Some pangolins walk with their front claws bent under the foot pad, furthermore, some exhibit a bipedal stance for some behaviors and may walk a few steps bipedally. Most of their diet consists of species of ants and termites and may be supplemented by other insects. They are somewhat particular and tend to only one or two species of insects, even when many species are available to them
18.
Phylum
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In biology, a phylum is a taxonomic rank below kingdom and above class. Traditionally, in botany the term division was used instead of phylum, although from 1993 the International Code of Nomenclature for algae, fungi, depending on definitions, the kingdom Animalia contains approximately 35 phyla, Plantae contains about 12, and Fungi contains around 7. Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta, the definitions of zoological phyla have changed from their origins in the six Linnaean classes and the four embranchements of Georges Cuvier. Haeckel introduced the term phylum, based on the Greek word phylon, in plant taxonomy, Eichler classified plants into five groups, named divisions. Informally, phyla can be thought of as grouping organisms based on general specialization of body plan, the most important objective measure in the above definitions is the certain degree—how unrelated do organisms need to be to be members of different phyla. The minimal requirement is that all organisms in a phylum should be more closely related to one another than to any other group. So phyla can be merged or split if it becomes apparent that they are related to one another or not, a definition of a phylum based on body plan has been proposed by paleontologists Graham Budd and Sören Jensen. By Budd and Jensens definition, a phylum is defined by a set of shared by all its living representatives. This approach brings some small problems—for instance, ancestral characters common to most members of a phylum may have been lost by some members, also, this definition is based on an arbitrary point of time, the present. However, as it is based, it is easy to apply to the fossil record. A greater problem is that it relies on a decision about which groups of organisms should be considered as phyla. However, proving that a fossil belongs to the group of a phylum is difficult. Furthermore, organisms in the group of a phylum can possess the body plan of the phylum without all the characteristics necessary to fall within it. This weakens the idea that each of the phyla represents a body plan. A classification using this definition may be affected by the chance survival of rare groups. Representatives of many modern phyla did not appear until long after the Cambrian, the kingdom Plantae is defined in various ways by different biologists. All definitions include the living embryophytes, to which may be added the two green algae divisions, Chlorophyta and Charophyta, to form the clade Viridiplantae. The table below follows the influential Cavalier-Smith system in equating Plantae with Archaeplastida, a group containing Viridiplantae, the definition and classification of plants at the division level also varies from source to source, and has changed progressively in recent years
19.
Family (biology)
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In biological classification, family is one of the eight major taxonomic ranks, it is classified between order and genus. A family may be divided into subfamilies, which are intermediate ranks above the rank of genus. In vernacular usage, a family may be named one of its common members, for example, walnuts and hickory trees belong to the family Juglandaceae. What does or does not belong to a family—or whether a family should be recognized at all—are proposed and determined by practicing taxonomists. There are no rules for describing or recognizing a family. Taxonomists often take different positions about descriptions of taxa, and there may be no broad consensus across the community for some time. Some described taxa are accepted broadly and quickly, but others only rarely, if at all, the naming of families is codified by various international codes. In zoological nomenclature, the names of animals end with the suffix -idae. The concept of rank at time was not yet settled, and in the preface to the Prodromus Magnol spoke of uniting his families into larger genera. Carolus Linnaeus used the word familia in his Philosophia botanica to denote groups of plants, trees, herbs, ferns, palms. He used this term only in the section of the book. In zoology, the family as an intermediate between order and genus was introduced by Pierre André Latreille in his Précis des caractères génériques des insectes. He used families in some but not in all his orders of insects, families can be used for evolutionary, palaeontological and generic studies because they are more stable than lower taxonomic levels such as genera and species
20.
Chordate
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Chordates are deuterostomes, as during the embryo development stage the anus forms before the mouth. They are also bilaterally symmetric coelomates, in the case of vertebrate chordates, the notochord is usually replaced by a vertebral column during development, and they may have body plans organized via segmentation. There are also additional extinct taxa, the Vertebrata are sometimes considered as a subgroup of the clade Craniata, consisting of chordates with a skull, the Craniata and Tunicata compose the clade Olfactores. Of the more than 65,000 living species of chordates, the worlds largest and fastest animals, the blue whale and peregrine falcon respectively, are chordates, as are humans. Fossil chordates are known from at least as early as the Cambrian explosion, Hemichordata, which includes the acorn worms, has been presented as a fourth chordate subphylum, but it now is usually treated as a separate phylum. The Hemichordata, along with the Echinodermata, form the Ambulacraria, the Chordata and Ambulacraria form the superphylum Deuterostomia, composed of the deuterostomes. Attempts to work out the relationships of the chordates have produced several hypotheses. All of the earliest chordate fossils have found in the Early Cambrian Chengjiang fauna. Because the fossil record of early chordates is poor, only molecular phylogenetics offers a prospect of dating their emergence. However, the use of molecular phylogenetics for dating evolutionary transitions is controversial and it has also proved difficult to produce a detailed classification within the living chordates. Attempts to produce family trees shows that many of the traditional classes are paraphyletic. While this has been known since the 19th century, an insistence on only monophyletic taxa has resulted in vertebrate classification being in a state of flux. Although the name Chordata is attributed to William Bateson, it was already in prevalent use by 1880, ernst Haeckel described a taxon comprising tunicates, cephalochordates, and vertebrates in 1866. Though he used the German vernacular form, it is allowed under the ICZN code because of its subsequent latinization, among the vertebrate sub-group of chordates the notochord develops into the spine, and in wholly aquatic species this helps the animal to swim by flexing its tail. In fish and other vertebrates, this develops into the spinal cord, the pharynx is the part of the throat immediately behind the mouth. In fish, the slits are modified to form gills, a muscular tail that extends backwards behind the anus. This is a groove in the wall of the pharynx. In filter-feeding species it produces mucus to gather food particles, which helps in transporting food to the esophagus and it also stores iodine, and may be a precursor of the vertebrate thyroid gland
21.
Taxonomic rank
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In biological classification, rank is the relative level of a group of organisms in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, order, class, phylum, kingdom, domain, a given rank subsumes under it less general categories, that is, more specific descriptions of life forms. Above it, each rank is classified within more general categories of organisms, the rank of any species and the description of its genus is basic, which means that to identify a particular organism, it is usually not necessary to specify ranks other than these first two. Consider a particular species, the red fox Vulpes vulpes, its next rank, as one group of the class Mammalia, all of the above are classified among those with backbones in the Chordata phylum rank, and with them among all the animals in the Animalia kingdom rank. Finally, all of the above will find their earliest relatives somewhere in their domain rank Eukarya, today, nomenclature is regulated by the nomenclature codes. There are seven main ranks, kingdom, phylum or division, class, order, family, genus. In addition, the domain is now used as one of the fundamental ranks. Also, this represents a synonym for the category of dominion. Unlike Moore, Whoese et al. did not suggest a Latin term for this category, a taxon is usually assigned a rank when it is given its formal name. The basic ranks are species and genus, when an organism is given a species name it is assigned to a genus, and the genus name is part of the species name. The species name is called a binomial, that is. For example, the name for the human species is Homo sapiens. This is usually italicized in print and underlined when italics are not available, in this case, Homo is the generic name and it is capitalized, sapiens indicates the species and it is not capitalized. There are definitions of the taxonomic ranks in the International Code of Zoological Nomenclature, superfamily, family, subfamily, tribe, subtribe, genus, subgenus. The International Code of Zoological Nomenclature divides names into family-group names, genus-group names, in the genus group and species group no further ranks are allowed. At higher ranks a lower level may be denoted by adding the prefix infra, meaning lower, a taxon above the rank of species has a scientific name in one part. A species has a composed of two parts, generic name + specific name, for example Canis lupus. A subspecies has a composed of three parts, generic name + specific name + subspecific name, for example Canis lupus familiaris
22.
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
23.
Cladogram
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A cladogram is a diagram used in cladistics to show relations among organisms. A cladogram uses lines that branch off in different directions ending at a clade, there are many shapes of cladograms but they all have lines that branch off from other lines. The lines can be traced back to where they branch off and these branching off points represent a hypothetical ancestor which can be inferred to exhibit the traits shared among the terminal taxa above it. This hypothetical ancestor might then provide clues about the order of evolution of features, adaptation. The characteristics used to create a cladogram can be categorized as either morphological or molecular. Prior to the advent of DNA sequencing, cladistic analysis primarily used morphological data, behavioral data may also be used. As DNA sequencing has become cheaper and easier, molecular systematics has become a more and more popular way to infer phylogenetic hypotheses. Another powerful method of reconstructing phylogenies is the use of genomic retrotransposon markers, researchers must decide which character states are ancestral and which are derived, because only synapomorphic character states provide evidence of grouping. This determination is usually done by comparison to the states of one or more outgroups. States shared between the outgroup and some members of the in-group are symplesiomorphies, states that are present only in a subset of the in-group are synapomorphies, note that character states unique to a single terminal do not provide evidence of grouping. The choice of an outgroup is a step in cladistic analysis because different outgroups can produce trees with profoundly different topologies. A homoplasy is a state that is shared by two or more taxa due to some cause other than common ancestry. The two main types of homoplasy are convergence and reversion, however, homoplasy is often not evident from inspection of the character itself, and is then detected by its incongruence on a most-parsimonious cladogram. Note that characters that are homoplastic may still contain phylogenetic signal, a well-known example of homoplasy due to convergent evolution would be the character, presence of wings. Though the wings of birds, bats, and insects serve the function, each evolved independently. Of course, the reason a homoplasy is recognizable in the first place is because there are other characters that imply a pattern of relationships that reveal its homoplastic distribution. A cladogram is the result of a parsimony analysis, which groups taxa on the basis of synapomorphies alone. There are many other algorithms that treat data somewhat differently
24.
Body plan
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A body plan, Bauplan, or ground plan is an assemblage of morphological features shared among many members of a phylum-level group. The vertebrate body plan is one of many, invertebrates consist of many phyla and this term, usually applied to animals, envisages a blueprint encompassing aspects such as symmetry, segmentation and limb disposition. Evolutionary developmental biology seeks to explain the origins of diverse body plans, the history of the discovery of body plans can be seen as a movement from a worldview centred on the vertebrates, to seeing the vertebrates as one body plan among many. For comparison, the number of phyla recognised by modern zoologists has risen to 35, in his 1735 book, Systema Naturæ, the Swedish botanist Linnaeus grouped the animals into quadrupeds, birds, amphibians, fish, insects and worms. Linnaeuss Vermes included effectively all other groups of animals, not only tapeworms, earthworms and leeches but molluscs, sea urchins and starfish, jellyfish, squid and cuttlefish. In his 1817 work, Le Règne Animal, the French zoologist Georges Cuvier combined evidence from comparative anatomy, ernst Haeckel, in his 1866 Generelle Morphologie der Organismen, asserted that all living things were monophyletic, being divided into plants, protista, and animals. His protista were divided into moneres, protoplasts, flagellates, diatoms, myxomycetes, myxocystodes, rhizopods and his animals were divided into groups with distinct body plans, he named these phyla. Haeckels animal phyla were coelenterates, echinoderms, and articulates, molluscs, stephen J. Gould explored the idea that the different phyla could be perceived in terms of a Bauplan, illustrating their fixity. However, he abandoned this idea in favor of punctuated equilibrium. Many body plans originated in the Cambrian period, in the Cambrian explosion, However, complete body plans of many phyla emerged much later, in the Palaeozoic or beyond. Thus the Cambrian explosion appears to have more or less completely replaced the earlier range of body plans, genes, embryos and development together determine the form of an adult organisms body, through the complex switching processes involved in morphogenesis. A key discovery was the existence of groups of homeobox genes, the homeobox genes are remarkably conserved between species as diverse as the fruit fly and man, the basic segmented pattern of the worm or fruit fly being the origin of the segmented spine in man. Developmental Biology 8e Online, Patterning of the Mesoderm by Activin Videos The Science of Evolution, Sean B. Carroll explains the genetics of the fruit fly body plan
25.
Exoskeleton
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An exoskeleton is the external skeleton that supports and protects an animals body, in contrast to the internal skeleton of, for example, a human. In usage, some of the kinds of exoskeletons are known as shells. Examples of animals with exoskeletons include insects such as grasshoppers and cockroaches, the shells of certain sponges and the various groups of shelled molluscs, including those of snails, clams, tusk shells, chitons and nautilus, are also exoskeletons. Some animals, such as the tortoise, have both an endoskeleton and an exoskeleton, exoskeletons have a role in defense from pests and predators, support, and in providing an attachment framework for musculature. Exoskeletons contain chitin, the addition of calcium carbonate makes them harder and stronger, ingrowths of the arthropod exoskeleton known as apodemes serve as attachment sites for muscles. These structures are composed of chitin, and are six times as strong. Similar to tendons, apodemes can stretch to store energy for jumping. Many different species produce exoskeletons, which are composed of a range of materials, bone, cartilage, or dentine is used in the Ostracoderm fish and turtles. Chitin forms the exoskeleton in arthropods including insects, arachnids such as spiders, crustaceans such as crabs and lobsters, calcium carbonates constitute the shells of molluscs, brachiopods, and some tube-building polychaete worms. Silica forms the exoskeleton in the microscopic diatoms and radiolaria, one species of mollusc, the scaly-foot gastropod, even makes use of the iron sulfides greigite and pyrite. Some organisms, such as some foraminifera, agglutinate exoskeletons by sticking grains of sand, contrary to a common misconception, echinoderms do not possess an exoskeleton, as their test is always contained within a layer of living tissue. Exoskeletons have evolved many times,18 lineages evolved calcified exoskeletons alone. Further, other lineages have produced tough outer coatings analogous to an exoskeleton and this coating is constructed from bone in the armadillo, and hair in the pangolin. The armor of reptiles like turtles and Ankylosaurs is constructed of bone, crocodiles have bony scutes, since exoskeletons are rigid, they present some limits to growth. Organisms with open shells can grow by adding new material to the aperture of their shell, as is the case in snails, bivalves, a true exoskeleton, like that found in arthropods, must be shed when it is outgrown. A new exoskeleton is produced beneath the old one, as the old one is shed, the new skeleton is soft and pliable. The animal will pump itself up to expand the new shell to maximal size, when the shell has set, the empty space inside the new skeleton can be filled up as the animal eats. Failure to shed the exoskeleton once outgrown can result in the animal being suffocated within its own shell and this is the mechanism behind some insect pesticides, such as Azadirachtin
26.
Protozoa
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In 21st-century systems of biological classification, the Protozoa are defined as a diverse group of unicellular eukaryotic organisms. Historically, protozoa were defined as single-celled animals or organisms with animal-like behaviors, such as motility, the group was regarded as the zoological counterpart to the protophyta, which were considered to be plant-like, as they are capable of photosynthesis. The terms protozoa and protozoans are now mostly used informally to designate single-celled, non-photosynthetic protists, such as the ciliates, amoebae and flagellates. The term Protozoa was introduced in 1818 for a taxonomic class, in several classification systems proposed by Thomas Cavalier-Smith and his collaborators since 1981, Protozoa is ranked as a kingdom. The seven-kingdom scheme proposed by Ruggiero et al. in 2015, places eight phyla under Protozoa, Euglenozoa, Amoebozoa, Metamonada, Choanozoa, Loukozoa, Percolozoa, Microsporidia and Sulcozoa. This kingdom does not form a clade, but an evolutionary grade or paraphyletic group, from which the fungi, for this reason, the terms protists, Protista or Protoctista are sometimes preferred for the high-level classification of eukaryotic microbes. In 2005, members of the Society of Protozoologists voted to change the name of organization to the International Society of Protistologists. The word protozoa was coined in 1818 by zoologist Georg August Goldfuss, as the Greek equivalent of the German Urthiere, meaning primitive, Goldfuss erected Protozoa as a class containing what he believed to be the simplest animals. Originally, the group included not only microbes, but also some lower animals, such as rotifers, corals, sponges, jellyfish, bryozoa. In 1848, in light of advancements in cell theory pioneered by Theodore Schwann and Matthias Schleiden, von Siebold redefined Protozoa to include only such unicellular forms, to the exclusion of all metazoa. At the same time, he raised the group to the level of a phylum containing two broad classes of microbes, Infusoria, and Rhizopoda. As a phylum under Animalia, the Protozoa were firmly rooted in the old two-kingdom classification of life, criticism of this system began in the latter half of the 19th century, with the realization that many organisms met the criteria for inclusion among both plants and animals. For example, the algae Euglena and Dinobryon have chloroplasts for photosynthesis, as an alternative, he proposed a new kingdom called Primigenum, consisting of both the protozoa and unicellular algae, which he combined together under the name Protoctista. In Hoggss conception, the animal and plant kingdoms were likened to two great pyramids blending at their bases in the Kingdom Primigenum, six years later, Ernst Haeckel also proposed a third kingdom of life, which he named Protista. Despite these proposals, Protozoa emerged as the taxonomic placement for heterotrophic microbes such as amoebae and ciliates. A variety of systems were proposed, and Kingdoms Protista and Protoctista became well established in biology texts. While many taxonomists have abandoned Protozoa as a group, Thomas Cavalier-Smith has retained it as a kingdom in the various classifications he has proposed. As of 2015, Cavalier-Smiths Protozoa excludes several major groups of organisms traditionally placed among the protozoa, including the ciliates, dinoflagellates, Protozoa, as traditionally defined, are mainly microscopic organisms, ranging in size from 10 to 52 micrometers
27.
Porifera
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Sponges are the basalmost clade of animals of the phylum Porifera. Sponges have unspecialized cells that can transform into other types and that often migrate between the cell layers and the mesohyl in the process. Sponges do not have nervous, digestive or circulatory systems, instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes. Sponges are similar to animals in that they are multicellular, heterotrophic, lack cell walls. Unlike other animals, they lack true tissues and organs, and have no body symmetry, the shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where it deposits nutrients, and leaves through a hole called the osculum. Many sponges have internal skeletons of spongin and/or spicules of calcium carbonate or silicon dioxide, all sponges are sessile aquatic animals. Although there are species, the great majority are marine species. A few species of sponge that live in food-poor environments have become carnivores that prey mainly on small crustaceans, most species use sexual reproduction, releasing sperm cells into the water to fertilize ova that in some species are released and in others are retained by the mother. The fertilized eggs form larvae which swim off in search of places to settle, sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. A few species reproduce by budding, the mesohyl functions as an endoskeleton in most sponges, and is the only skeleton in soft sponges that encrust hard surfaces such as rocks. More commonly, the mesohyl is stiffened by mineral spicules, by spongin fibers or both, demosponges use spongin, and in many species, silica spicules and in some species, calcium carbonate exoskeletons. Demosponges constitute about 90% of all known species, including all freshwater ones. The fragile glass sponges, with scaffolding of silica spicules, are restricted to polar regions, fossils of all of these types have been found in rocks dated from 580 million years ago. In addition Archaeocyathids, whose fossils are common in rocks from 530 to 490 million years ago, are now regarded as a type of sponge, the single-celled choanoflagellates resemble the choanocyte cells of sponges which are used to drive their water flow systems and capture most of their food. This along with studies of ribosomal molecules have been used as morphological evidence to suggest sponges are the sister group to the rest of animals. Some studies have shown that sponges do not form a group, in other words do not include all. Recent phylogenetic analyses suggest that comb jellies rather than sponges are the group to the rest of animals. By the 1950s, though, these had been overfished so heavily that the industry almost collapsed, sponges and their microscopic endosymbionts are now being researched as possible sources of medicines for treating a wide range of diseases
28.
Coelenterata
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Coelenterata is a term encompassing the animal phyla Cnidaria and Ctenophora. The name comes from the Greek koilos and enteron, referring to the body cavity common to these two phyla. They have very simple organization, with only two layers of cells, and radial symmetry. Some examples are corals, which are colonial, and hydra, jelly fish. Coelenterata lack a specialized circulatory system relying instead on diffusion across the tissue layers, all coelenterates are aquatic, mostly marine. The body has an opening, the hypostome, surrounded by sensory tentacles equipped with either nematocysts or colloblasts to capture mostly planktonic prey. These tentacles surround a spacious cavity called the gastrovascular cavity or coelenteron, digestion is both intracellular and extracellular. Respiration and excretion are accomplished by simple diffusion, a network of nerves is spread throughout the body. Many forms exhibit polymorphism, wherein different types of individuals are present in a colony for different functions and these animals generally reproduce asexually by budding, though sexual reproduction does occur in some groups. The scientific validity of the term coelenterate is currently disputed, as the Cnidaria, coelentera may only be monophyletic if both Placozoa and Bilateria are included. In particular, the position of Ctenophora is controversial, it was first considered a sub-group of coelenterata. Some researchers suggest that Coelenterata is not monophyletic, and therefore any group containing Cnidaria and Ctenophora, however, some genomic studies have found support for monophyletic coelenterates. Despite this uncertainty, the term coelenterate is still used in informal settings to refer to the Cnidaria, complicating the issue is the 1997 work of Lynn Margulis that placed the Cnidaria and Ctenophora alone in the branch Radiata within Eumetazoa. Neither grouping is accepted universally, however, both are commonly encountered in taxonomic literature
29.
Flatworm
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The flatworms, flat worms, Platyhelminthes, Plathelminthes, or platyhelminths are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates. The digestive cavity has one opening for both ingestion and egestion, as a result, the food cannot be processed continuously. Free-living flatworms are mostly predators, and live in water or in shaded, humid terrestrial environments, cestodes and trematodes have complex life-cycles, with mature stages that live as parasites in the digestive systems of fish or land vertebrates, and intermediate stages that infest secondary hosts. Unlike the other groups, the monogeneans are external parasites infesting aquatic animals. Because they do not have internal body cavities, Platyhelminthes were regarded as a stage in the evolution of bilaterians. However, analyses since the mid-1980s have separated out one subgroup, the remaining Platyhelminthes form a monophyletic group, one that contains all and only descendants of a common ancestor that is itself a member of the group. The redefined Platyhelminthes is part of the Lophotrochozoa, one of the three groups of more complex bilaterians. Hence, the traditional platyhelminth subgroup Turbellaria is now regarded as paraphyletic, since it excludes the wholly parasitic groups, over half of all known flatworm species are parasitic, and some do enormous harm to humans and their livestock. Schistosomiasis, caused by one genus of trematodes, is the second-most devastating of all diseases caused by parasites. Neurocysticercosis, which arises when larvae of the pork tapeworm Taenia solium penetrate the central system, is the major cause of acquired epilepsy worldwide. The threat of parasites to humans in developed countries is rising because of the popularity of raw or lightly cooked foods. However, there is now concern that these planarians may themselves become a threat to native snails. In northwest Europe, there are concerns about the spread of the New Zealand planarian Arthurdendyus triangulatus, like other bilaterians, they have three main cell layers, while the radially symmetrical cnidarians and ctenophores have only two cell layers. Beyond that, they are defined more by what they do not have than by any particular series of specializations, unlike other bilaterians, Platyhelminthes have no internal body cavity, so are described as acoelomates. They also lack specialized circulatory and respiratory organs, both of these facts are defining features when classifying a flatworms anatomy and their bodies are soft and unsegmented. The lack of circulatory and respiratory organs limits platyhelminths to sizes and shapes that enable oxygen to reach, hence, many are microscopic and the large species have flat ribbon-like or leaf-like shapes. The guts of large species have many branches, allowing nutrients to diffuse to all parts of the body, the mesenchyme contains all the internal organs and allows the passage of oxygen, nutrients and waste products. Most platyhelminths have no anus and regurgitate undigested material through the mouth, however, some long species have an anus and some with complex, branched guts have more than one anus, since excretion only through the mouth would be difficult for them
30.
Nematode
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The nematodes or roundworms constitute the phylum Nematoda. They are an animal phylum inhabiting a broad range of environments. Nematodes are classified along with insects and other moulting animals in the clade Ecdysozoa, Nematodes have successfully adapted to nearly every ecosystem from marine to fresh water, to soils, and from the polar regions to the tropics, as well as the highest to the lowest of elevations. They are found in part of the earths lithosphere, even at great depths below the surface of the Earth in gold mines in South Africa. They represent 90% of all animals on the ocean floor, the many parasitic forms include pathogens in most plants and animals. The location of towns would be decipherable, since for every massing of human beings there would be a corresponding massing of certain nematodes, trees would still stand in ghostly rows representing our streets and highways. In 1758, Linnaeus described some nematode genera, then included in Vermes, the name of the group Nematoda, informally called nematodes, came from Nematoidea, originally defined by Karl Rudolphi, from Ancient Greek νῆμα and -eiδἠς. It was treated as family Nematodes by Burmeister, at its origin, the Nematoidea erroneously included Nematodes and Nematomorpha, attributed by von Siebold. Along with Acanthocephala, Trematoda and Cestoidea, it formed the obsolete group Entozoa and they were also classed along with Acanthocephala in the obsolete phylum Nemathelminthes by Gegenbaur. In 1861, K. M. Diesing treated the group as order Nematoda, in 1877, the taxon Nematoidea, including the family Gordiidae, was promoted to the rank of phylum by Ray Lankester. In 1919, Nathan Cobb proposed that nematodes should be recognized alone as a phylum and he argued they should be called nema in English rather than nematodes and defined the taxon Nemates, listing Nematoidea sensu restricto as a synonym. Since Cobb was the first to all but nematodes from the group, some sources consider the valid taxon name to be Nemates or Nemata. The phylogenetic relationships of the nematodes and their close relatives among the protostomian Metazoa are unresolved, traditionally, they were held to be a lineage of their own but in the 1990s, they were proposed to form the group Ecdysozoa together with moulting animals, such as arthropods. The identity of the closest living relatives of the Nematoda has always considered to be well resolved. Morphological characters and molecular phylogenies agree with placement of the roundworms as a taxon to the parasitic Nematomorpha. Together with the Scalidophora, the Nematoida form the clade Cycloneuralia, the Cycloneuralia or the Introverta—depending on the validity of the former—are often ranked as a superphylum. Due to the lack of knowledge regarding many nematodes, their systematics is contentious, an earliest and influential classification was proposed by Chitwood and Chitwood—later revised by Chitwood—who divided the phylum into two—the Aphasmidia and the Phasmidia. These were later renamed Adenophorea and Secernentea, respectively, the Secernentea share several characteristics, including the presence of phasmids, a pair of sensory organs located in the lateral posterior region, and this was used as the basis for this division
31.
Annelid
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The annelids, also known as the ringed worms or segmented worms, are a large phylum, with over 17,000 extant species including ragworms, earthworms, and leeches. The annelids are bilaterally symmetrical, triploblastic, coelomate, invertebrate organisms and they also have parapodia for locomotion. Most textbooks still use the division into polychaetes, oligochaetes. Cladistic research since 1997 has radically changed this scheme, viewing leeches as a sub-group of oligochaetes and oligochaetes as a sub-group of polychaetes, in addition, the Pogonophora, Echiura and Sipuncula, previously regarded as separate phyla, are now regarded as sub-groups of polychaetes. Annelids are considered members of the Lophotrochozoa, a super-phylum of protostomes that also includes molluscs, brachiopods, flatworms, the basic annelid form consists of multiple segments. Each segment has the same sets of organs and, in most polychates, has a pair of parapodia that many use for locomotion. Septa separate the segments of many species, but are defined or absent in others. The septa of such species also enable them to change the shapes of individual segments, although many species can reproduce asexually and use similar mechanisms to regenerate after severe injuries, sexual reproduction is the normal method in species whose reproduction has been studied. The minority of living polychaetes whose reproduction and lifecycles are known produce trochophore larvae, Oligochaetes are full hermaphrodites and produce a ring-like cocoon around their bodies, in which the eggs and hatchlings are nourished until they are ready to emerge. Earthworms are Oligochaetes that support terrestrial food chains both as prey and in some regions are important in aeration and enriching of soil, in addition to improving soil fertility, annelids serve humans as food and as bait. Scientists observe annelids to monitor the quality of marine and fresh water, although blood-letting is no longer in favor with doctors, some leech species are regarded as endangered species because they have been over-harvested for this purpose in the last few centuries. Ragworms jaws are now being studied by engineers as they offer a combination of lightness. Since annelids are soft-bodied, their fossils are rare – mostly jaws, although some late Ediacaran fossils may represent annelids, the oldest known fossil that is identified with confidence comes from about 518 million years ago in the early Cambrian period. Fossils of most modern mobile polychaete groups appeared by the end of the Carboniferous, there are over 22,000 living annelid species, ranging in size from microscopic to the Australian giant Gippsland earthworm and Amynthas mekongianus, which can both grow up to 3 metres long. As their name suggests, they have multiple chetae per segment, polychaetes have parapodia that function as limbs, and nuchal organs that are thought to be chemosensors. Most are marine animals, although a few live in fresh water. These have few or no chetae per segment, and no nuchal organs or parapodia, the clitellates are sub-divided into, Oligochaetes, which includes earthworms. Oligochaetes have a pad in the roof of the mouth
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Arachnid
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Arachnids are a class of joint-legged invertebrate animals, in the subphylum Chelicerata. The term is derived from the Greek word ἀράχνη, meaning spider, spiders are the largest order in the class. Almost all extant arachnids are terrestrial, living mainly on land, however, some inhabit freshwater environments and, with the exception of the pelagic zone, marine environments as well. They comprise over 100,000 named species, including spiders, scorpions, harvestmen, ticks, mites, almost all adult arachnids have eight legs, and arachnids may be easily distinguished from insects by this fact, since insects have six legs. However, arachnids also have two pairs of appendages that have become adapted for feeding, defense, and sensory perception. The first pair, the chelicerae, serve in feeding and defense, the next pair of appendages, the pedipalps, have been adapted for feeding, locomotion, and/or reproductive functions. In Solifugae, the palps are quite leg-like, so that animals appear to have ten legs. The larvae of mites and Ricinulei have only six legs, a fourth pair usually appears when they moult into nymphs, however, mites are variable, as well as eight, there are adult mites with six or even four legs. Arachnids are further distinguished from insects by the fact they do not have antennae or wings and their body is organized into two tagmata, called the prosoma, or cephalothorax, and the opisthosoma, or abdomen. The cephalothorax is derived from the fusion of the cephalon and the thorax, the abdomen is segmented in the more primitive forms, but varying degrees of fusion between the segments occur in many groups. It is typically divided into a preabdomen and postabdomen, although this is clearly visible in scorpions, and in some orders, such as the Acari. A telson is present in scorpions, where it has modified to a stinger. Like all arthropods, arachnids have an exoskeleton, and they also have a structure of cartilage-like tissue, called the endosternite. The endosternite is even calcified in some Opiliones, most arachnids lack extensor muscles in the distal joints of their appendages. Spiders and whipscorpions extend their limbs hydraulically using the pressure of their hemolymph, solifuges and some harvestmen extend their knees by the use of highly elastic thickenings in the joint cuticle. Scorpions, pseudoscorpions and some harvestmen have evolved muscles that extend two leg joints at once, the equivalent joints of the pedipalps of scorpions though, are extended by elastic recoil. This type of system has almost certainly evolved from the book lungs. The excretory glands of arachnids include up to four pairs of coxal glands along the side of the prosoma, many arachnids have only one or the other type of excretory gland, although several do have both
33.
Insecta
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Insects are a class of hexapod invertebrates within the arthropod phylum that have a chitinous exoskeleton, a three-part body, three pairs of jointed legs, compound eyes and one pair of antennae. They are the most diverse group of animals on the planet, including more than a million described species, the number of extant species is estimated at between six and ten million, and potentially represent over 90% of the differing animal life forms on Earth. Insects may be found in all environments, although only a small number of species reside in the oceans. The life cycles of insects vary but most hatch from eggs, insect growth is constrained by the inelastic exoskeleton and development involves a series of molts. The immature stages can differ from the adults in structure, habit and habitat, Insects that undergo 3-stage metamorphosis lack a pupal stage and adults develop through a series of nymphal stages. The higher level relationship of the Hexapoda is unclear, fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 55 to 70 cm. The most diverse insect groups appear to have coevolved with flowering plants, adult insects typically move about by walking, flying or sometimes swimming. As it allows for rapid yet stable movement, many insects adopt a tripedal gait in which they walk with their legs touching the ground in alternating triangles, Insects are the only invertebrates to have evolved flight. Many insects spend at least part of their lives under water, with adaptations that include gills. Some species, such as water striders, are capable of walking on the surface of water, Insects are mostly solitary, but some, such as certain bees, ants and termites, are social and live in large, well-organized colonies. Some insects, such as earwigs, show maternal care, guarding their eggs, Insects can communicate with each other in a variety of ways. Male moths can sense the pheromones of female moths over great distances, other species communicate with sounds, crickets stridulate, or rub their wings together, to attract a mate and repel other males. Lampyridae in the beetle order communicate with light, humans regard certain insects as pests, and attempt to control them using insecticides and a host of other techniques. Some insects damage crops by feeding on sap, leaves or fruits, a few parasitic species are pathogenic. Some insects perform complex ecological roles, blow-flies, for example, help consume carrion, Many other insects are considered ecologically beneficial as predators and a few provide direct economic benefit. Silkworms and bees have been used extensively by humans for the production of silk and honey, in some cultures, people eat the larvae or adults of certain insects. Insect first appears documented in English in 1601 in Hollands translation of Pliny, translations of Aristotles term also form the usual word for insect in Welsh, Serbo-Croatian, Russian, etc. The evolutionary relationship of insects to other animal groups remains unclear, in the Pancrustacea theory, insects, together with Entognatha, Remipedia, and Cephalocarida, make up a natural clade labeled Miracrustacea
34.
Coral
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Corals are marine invertebrates in the class Anthozoa of phylum Cnidaria. They typically live in colonies of many identical individual polyps. The group includes the important reef builders that inhabit tropical oceans, a coral group is a colony of myriad genetically identical polyps. Each polyp is an animal typically only a few millimeters in diameter. A set of tentacles surround a central mouth opening, an exoskeleton is excreted near the base. Over many generations, the colony creates a large skeleton that is characteristic of the species. Individual heads grow by reproduction of polyps. Corals also breed sexually by spawning, polyps of the same species release gametes simultaneously over a period of one to several nights around a full moon and these are commonly known as zooxanthellae and the corals that contain them are zooxanthellate corals. Such corals require sunlight and grow in clear, shallow water, other corals do not rely on zooxanthellae and can live in much deeper water, with the cold-water genus Lophelia surviving as deep as 3,000 metres. Some have been found on the Darwin Mounds, north-west of Cape Wrath, Corals have also been found as far north as off the coast of Washington State and the Aleutian Islands. In his Scala Naturae, Aristotle classified corals as zoophyta, animals that had characteristics of plants and were therefore hypothetically in between animals and plants, the Persian polymath Al-Biruni classified sponges and corals as animals, arguing that they respond to touch. The phylogeny of Anthozoans is not clearly understood and a number of different models have been proposed, within the Hexacorallia, the sea anemones, coral anemones and stony corals may constitute a monophyletic grouping united by their eight-fold symmetry and cnidocyte trait. The Octocorallia appears to be monophyletic, and primitive members of this group may have been stolonate, the cladogram presented here comes from a 2014 study by Stampar et al. which was based on the divergence of mitochondrial DNA within the group and on nuclear markers. Corals are classified in the class Anthozoa of the phylum Cnidaria and they are divided into three subclasses, Hexacorallia, Octocorallia, and Ceriantharia. The Hexacorallia include the stony corals, the sea anemones and the zoanthids and these groups have polyps that generally have 6-fold symmetry. The Octocorallia include blue coral, soft corals, sea pens and these groups have polyps with 8-fold symmetry, each polyp having eight tentacles and eight mesenteries. Fire corals are not true corals, being in the order Anthomedusa of the class Hydrozoa, Corals are sessile animals in the class Anthozoa and differ from most other cnidarians in not having a medusa stage in their life cycle. The body unit of the animal is a polyp, most corals are colonial, the initial polyp budding to produce another and the colony gradually developing from this small start
35.
Anthozoa
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Anthozoa is a class within the phylum Cnidaria. Unlike other cnidarians, anthozoans do not have a stage in their development. Instead, they release sperm and eggs that form a planula, some anthozoans can also reproduce asexually through budding. More than 6,100 species have been described, the name comes from the Greek words άνθος and ζώα, hence ανθόζωα = flower animals, a reference to the floral appearance of their perennial polyp stage. Like those of cnidarians, the individual polyps have a cylindrical body crowned by a ring of tentacles surrounding the mouth. The mouth leads into a tubular pharynx which descends for some distance into the body opening into the gastrovascular cavity that fills the interior of the body. Unlike other cnidarians, however, the cavity is subdivided by a number of radiating partitions, the gonads are also located within the cavity walls. All cnidarian species can feed by catching prey with nematocysts, sea anemones are capable of catching fish, anemones and certain species of coral live in isolation, however, most corals form colonies of genetically identical polyps. These closely resemble anemones in structure, although they are much smaller. Stony coral are found in most seas, the extant orders are shown to the right. Hexacorallia includes coral reef builders, the corals, sea anemones. Genetic studies of ribosomal DNA has shown Ceriantharia to be a monophyletic group, sea whips and sea fans, known as gorgonians, are part of Alcyonacea and historically were divided into separate orders. Ceriantharia comprises the related tube-dwelling anemones, tube-dwelling anemones or cerianthids look very similar to sea anemones, but belong to an entirely different subclass of anthozoans. They are solitary, living buried in soft sediments, tube anemones live and can withdraw into tubes, which are made of a fibrous material, which is made from secreted mucus and threads of nematocyst-like organelles, known as ptychocysts. A number of orders of corals have been classified as their calcium skeleton forms a prolific fossil record. Data related to Anthozoa at Wikispecies
36.
Onychophora
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Onychophora, commonly known as velvet worms or more ambiguously as peripatus, is a phylum of elongate, soft-bodied, many-legged panarthropods. In appearance they have variously compared to worms with legs, caterpillars. They prey upon animals such as insects, which they catch by squirting an adhesive slime. Approximately 200 species have been described, although the number of species is likely greater. The two extant families of velvet worms are Peripatidae and Peripatopsidae and they show a peculiar distribution, with the peripatids being predominantly equatorial and tropical, while the peripatopsids are all found south of the equator. It is the only phylum within animalia that is endemic to terrestrial environments. Velvet worms are considered relatives of the Arthropoda and Tardigrada. This makes them of palaeontological interest, as they can reconstruct the ancestral arthropod. In modern zoology, they are renowned for their curious mating behaviour. Velvet worms are segmented animals with a cylindrical body cross-section. The animals grow to between 0.5 and 20 cm, with the average being about 5 cm, and have between 13 and 43 pairs of legs. Segmentation is outwardly inconspicuous, and identifiable by the spacing of the pairs of legs and in the regular arrangement of skin pores. The individual body sections are largely unspecialised, even the head develops only a little differently from the abdominal segments, the stub feet that characterise the velvet worms are conical, baggy appendages of the body, which are internally hollow and have no joints. Although the number of feet can vary considerably between species, their structure is very similar. Rigidity is provided by the pressure of their fluid contents. However, each leg can also be shortened and bent by internal muscles, due to the lack of joints, this bending can take place at any point along the sides of the leg. In some species, two different organs are found within the feet, Crural glands are situated at the shoulder of the legs and they open outwards at the crural papillae—small wart-like bumps on the belly side of the leg—and secrete chemical messenger materials called pheromones. Their name comes from the Latin cruralis meaning of the legs, coxal vesicles are pouches located on the belly side of the leg, which can be everted and probably serve in water absorption
37.
Horseshoe crab
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Horseshoe crabs are marine arthropods of the family Limulidae and order Xiphosura or Xiphosurida. They are invertebrates meaning that they lack a spine, horseshoe crabs live primarily in and around shallow ocean waters on soft sandy or muddy bottoms. They occasionally come onto shore to mate and they are commonly used as bait and in fertilizer. In recent years, a decline in the population has occurred as a consequence of coastal destruction in Japan. Tetrodotoxin may be present in the roe of species inhabiting the waters of Thailand, because of their origin 450 million years ago, horseshoe crabs are considered living fossils. They belong to a separate subphylum, Chelicerata, and are related to arachnids. The earliest horseshoe crab fossils are found in strata from the late Ordovician period, the latter become functional just before the embryo hatches. Also, a pair of eyes is located near the mouth. The horseshoe crab has 5 additional eyes on top of its shell, the mouth is located in the center of the legs, whose bases are referred to as gnathobases and have the same function as jaws and help grind up food. The horseshoe crab has five pairs of legs for walking, swimming, the long, straight, rigid tail can be used to flip the animal over if turned upside down, so a horseshoe crab with a broken tail is susceptible to desiccation or predation. Behind its legs, the crab has book gills, which exchange respiratory gases. As in other arthropods, a true endoskeleton is absent, and they are more often found on the ocean floor searching for worms and molluscs, which are their main food. They may also feed on crustaceans and even small fish, females are larger than males, C. rotundicauda is the size of a human hand, while L. polyphemus can be up to 60 cm long. The juveniles grow about 33% larger with every molt until reaching adult size, during the breeding season, horseshoe crabs migrate to shallow coastal waters. A male selects a female and clings to her back, often, several males surround the female and all fertilize together which makes it easy to spot and count females as they are the large center carapace surrounded by 3-5 smaller ones. The female digs a hole in the sand and lays her eggs while the male fertilize them, the female can lay between 60,000 and 120,000 eggs in batches of a few thousand at a time. The eggs take about two weeks to hatch, shore birds eat many of them before they hatch, the larvae molt six times during the first year. Raising horseshoe crabs in captivity has proven to be difficult, some evidence indicates mating takes place only in the presence of the sand or mud in which the horseshoe crabs eggs were hatched
38.
Xiphosura
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The Xiphosura are an order of marine merostome chelicerates that includes a large number of extinct lineages and only four extant species in the family Limulidae, which includes the horseshoe crabs. The group has changed in millions of years, the modern horseshoe crabs look almost identical to prehistoric genera such as the Jurassic Mesolimulus. The most notable difference between ancient and modern forms is that the segments in present species are fused into a single unit in adults. Xiphosura were traditionally placed in the class Merostomata, although this term was intended to also the eurypterids. Although the name Merostomata is still seen in textbooks, without reference to the Eurypterida, the Merostomata label originally did not include Eurypterida, although they were added in as a better understanding of the extinct group evolved. Modern xiphosurans reach up to 60 cm in length, but the Paleozoic species were often far smaller. Their bodies are covered with a cuticle, but do not contain any crystalline biominerals, and are divided into an anterior prosoma. The upper surface of the prosoma is covered by a carapace, while the underside bears five pairs of walking legs. The mouth is located below the tip of the carapace. Xiphosurans have up to four eyes, located in the carapace, a pair of compound eyes is on the side of the prosoma, with one or two median ocelli towards the front. The compound eyes are simpler in structure than those of other arthropods and they can probably detect movement, but are unlikely to be able to form a true image. In front of the ocelli is an organ that probably functions as a chemoreceptor. The first four pairs of legs end in pincers, and have a series of spines, called the gnathobase, the spines are used to masticate the food, tearing it up before passing it to the mouth. The fifth and final pair of legs, however, has no pincers or spines, instead having structures for cleaning the gills, behind the walking legs is a sixth set of appendages, the chilaria, which are greatly reduced in size and covered in hairs and spines. These are thought to be vestiges of the limbs of an absorbed first opisthosomal segment, the opisthosoma is divided into a forward mesosoma, with flattened appendages, and a metasoma at the rear, which has no appendages. In modern forms, the whole of the opisthosoma is fused into a single unsegmented structure, the underside of the opisthosoma carries the genital openings and five pairs of flap-like gills. The opisthosoma terminates in a caudal spine, commonly referred to as a telson. The spine is highly mobile, and is used to push the animal if it is accidentally turned over
39.
Sponge
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Sponges are the basalmost clade of animals of the phylum Porifera. Sponges have unspecialized cells that can transform into other types and that often migrate between the cell layers and the mesohyl in the process. Sponges do not have nervous, digestive or circulatory systems, instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes. Sponges are similar to animals in that they are multicellular, heterotrophic, lack cell walls. Unlike other animals, they lack true tissues and organs, and have no body symmetry, the shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where it deposits nutrients, and leaves through a hole called the osculum. Many sponges have internal skeletons of spongin and/or spicules of calcium carbonate or silicon dioxide, all sponges are sessile aquatic animals. Although there are species, the great majority are marine species. A few species of sponge that live in food-poor environments have become carnivores that prey mainly on small crustaceans, most species use sexual reproduction, releasing sperm cells into the water to fertilize ova that in some species are released and in others are retained by the mother. The fertilized eggs form larvae which swim off in search of places to settle, sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. A few species reproduce by budding, the mesohyl functions as an endoskeleton in most sponges, and is the only skeleton in soft sponges that encrust hard surfaces such as rocks. More commonly, the mesohyl is stiffened by mineral spicules, by spongin fibers or both, demosponges use spongin, and in many species, silica spicules and in some species, calcium carbonate exoskeletons. Demosponges constitute about 90% of all known species, including all freshwater ones. The fragile glass sponges, with scaffolding of silica spicules, are restricted to polar regions, fossils of all of these types have been found in rocks dated from 580 million years ago. In addition Archaeocyathids, whose fossils are common in rocks from 530 to 490 million years ago, are now regarded as a type of sponge, the single-celled choanoflagellates resemble the choanocyte cells of sponges which are used to drive their water flow systems and capture most of their food. This along with studies of ribosomal molecules have been used as morphological evidence to suggest sponges are the sister group to the rest of animals. Some studies have shown that sponges do not form a group, in other words do not include all. Recent phylogenetic analyses suggest that comb jellies rather than sponges are the group to the rest of animals. By the 1950s, though, these had been overfished so heavily that the industry almost collapsed, sponges and their microscopic endosymbionts are now being researched as possible sources of medicines for treating a wide range of diseases
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International Union for Conservation of Nature
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The International Union for Conservation of Nature is an international organization working in the field of nature conservation and sustainable use of natural resources. It is involved in gathering and analysis, research, field projects, advocacy, lobbying. IUCNs mission is to influence, encourage and assist societies throughout the world to conserve nature and to ensure that any use of resources is equitable. Over the past decades, IUCN has widened its focus beyond conservation ecology and now incorporates issues related to equality, poverty alleviation. Unlike other international NGOs, IUCN does not itself aim to mobilize the public in support of nature conservation and it tries to influence the actions of governments, business and other stakeholders by providing information and advice, and through lobbying and partnerships. The organization is best known to the public for compiling and publishing the IUCN Red List. IUCN has a membership of over 1200 governmental and non-governmental organizations, some 11,000 scientists and experts participate in the work of IUCN commissions on a voluntary basis. It employs approximately 1000 full-time staff in more than 60 countries and its headquarters are in Gland, Switzerland. IUCN has observer and consultative status at the United Nations, and plays a role in the implementation of several conventions on nature conservation. It was involved in establishing the World Wide Fund for Nature, in the past, IUCN has been criticized for placing the interests of nature over those of indigenous peoples. In recent years, its relations with the business sector have caused controversy. It was previously called the International Union for Protection of Nature, establishment In 1947, the Swiss League for the Protection of Nature organised an international conference on the protection of nature in Brunnen. It is considered to be the first government-organized non-governmental organization, the initiative to set up the new organisation came from UNESCO and especially from its first Director General, the British biologist Julian Huxley. At the time of its founding IUPN was the international organisation focusing on the entire spectrum of nature conservation Early years. Its secretariat was located in Brussels and its first work program focused on saving species and habitats, increasing and applying knowledge, advancing education, promoting international agreements and promoting conservation. Providing a solid base for conservation action was the heart of all activities. IUPN and UNESCO were closely associated and they jointly organized the 1949 Conference on Protection of Nature. In preparation for this conference a list of endangered species was drawn up for the first time
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Homology (biology)
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In biology, homology is the existence of shared ancestry between a pair of structures, or genes, in different taxa. Evolutionary biology explains homologous structures adapted to different purposes as the result of descent with modification from a common ancestor, examples include the legs of a centipede, the maxillary palp and labial palp of an insect, and the spinous processes of successive vertebrae in a vertebral column. Sequence homology between protein or DNA sequences is defined in terms of shared ancestry. Two segments of DNA can have shared ancestry because of either an event or a duplication event. Homology among proteins or DNA is inferred from their sequence similarity, significant similarity is strong evidence that two sequences are related by divergent evolution from a common ancestor. Alignments of multiple sequences are used to discover the homologous regions, the word homology, coined in about 1656, derives from the Greek ὁμόλογος homologos from ὁμός homos same and λόγος logos relation. Homology is the relationship between biological structures or sequences that are derived from a common ancestor, for example, many insects possess two pairs of flying wings. In beetles, the first pair of wings has evolved into a pair of hard wing covers, the same major forearm bones are found in fossils of lobe-finned fish such as Eusthenopteron. The opposite of homologous organs are analogous organs which do similar jobs in two taxa that were not present in their last common ancestor but rather evolved separately. For example, the wings of insects and birds evolved independently in widely separated groups, similarly, the wings of a sycamore maple seed and the wings of a bird are analogous but not homologous, as they develop from quite different structures. A structure can be homologous at one level, but only analogous at another, for example, in the pterosaurs, the wing involves both the forelimb and the hindlimb. Analogy is called homoplasy in cladistics, and convergent or parallel evolution in evolutionary biology, specialised terms are used in taxonomic research. Primary homology is that initially conjectured by a researcher based on similar structure or anatomical connections, secondary homology is implied by parsimony analysis, where a character that only occurs once on a tree is taken to be homologous. As implied in this definition, many cladists consider homology to be synonymous with synapomorphy, homologies provide the fundamental basis for all biological classification, although some may be highly counter-intuitive. The homologies between these have been discovered by comparing genes in evolutionary developmental biology, among insects, the stinger of the female honey bee is a modified ovipositor, homologous with ovipositors in other insects such as the Orthoptera, Hemiptera, and those Hymenoptera without stingers. The three small bones in the ear of mammals including humans, the malleus, incus. The malleus and incus develop in the embryo from structures that form jaw bones in lizards, both lines of evidence show that these bones are homologous, sharing a common ancestor. Among the many homologies in mammal reproductive systems, ovaries and testicles are homologous, in many plants, defensive or storage structures are made by modifications of the development of primary leaves, stems, and roots
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Tortoise
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Tortoises are a family, Testudinidae, of land-dwelling reptiles in the order Testudines. Tortoises are shielded from predators by a shell, the top part of the shell is the carapace, the underside is the plastron, and the two are connected by the bridge. The carapace is fused to both the vertebrae and ribcage, and tortoises are unique among vertebrates in that the pectoral, Tortoises can vary in size from a few centimeters to two meters. They are usually diurnal animals with tendencies to be depending on the ambient temperatures. Tortoises are the longest living animal in the world, although the longest living species of tortoise is a matter of debate. Galapagos tortoises are noted to live over 150 years, but an Aldabra giant tortoise named Adwaita may having been the longest living at an estimated 255 years. It is important to note that tortoises are not the longest living animal, period, with bowhead whales reaching over 200 years, and the ocean quahog clam reaching 500 years old. Differences exist in usage of the common terms turtle, tortoise and these terms are common names and do not reflect precise biological or taxonomic distinctions. In America, for example, the members of the genus Terrapene dwell on land, in Britain, terrapin is used to refer to a larger group of semiaquatic turtles than the restricted meaning in America. Australian usage is different from both American and British usage, land tortoises are not native to Australia, yet traditionally freshwater turtles have been called tortoises in Australia. Female tortoises dig nesting burrows in which lay from one to 30 eggs. Egg-laying typically occurs at night, after which the mother covers her clutch with sand, soil. The eggs are unattended, and depending on the species. The size of the egg depends on the size of the mother, the plastron of a female tortoise often has a noticeable V-shaped notch below the tail which facilitates passing the eggs. Upon completion of the period, a fully formed hatchling uses an egg tooth to break out of its shell. It digs to the surface of the nest and begins a life of survival on its own and they are hatched with an embryonic egg sac which serves as a source of nutrition for the first three to seven days until they have the strength and mobility to find food. Juvenile tortoises often require a different balance of nutrients than adults, for example, the young of a strictly herbivorous species commonly will consume worms or insect larvae for additional protein. Moreover, some tortoises grow more than one ring per season, Tortoises generally have one of the longest lifespans of any animal, and some individuals are known to have lived longer than 150 years
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Snail
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Snail is a common name that is applied most often to land snails, terrestrial pulmonate gastropod molluscs. However, the common name snail is also applied to most of the members of the molluscan class Gastropoda that have a shell that is large enough for the animal to retract completely into. When the word snail is used in this most general sense, it not just land snails but also thousands of species of sea snails. Occasionally a few other molluscs that are not actually gastropods, such as the Monoplacophora, snail-like animals that naturally lack a shell, or have only an internal shell, are mostly called slugs, and land snails that have only a very small shell are often called semi-slugs. Even a few species have lungs. Snails can be found in a wide range of environments, including ditches, deserts. Although land snails may be familiar to laymen, marine snails constitute the majority of snail species, and have much greater diversity. Numerous kinds of snail can also be found in fresh water, most snails have thousands of microscopic tooth-like structures located on a banded ribbon-like tongue called a radula. The radula works like a file, ripping food into small pieces, many snails are herbivorous, eating plants or rasping algae from surfaces with their radulae, though a few land species and many marine species are omnivores or predatory carnivores. Several species of the genus Achatina and related genera are known as giant African land snails, some grow to 15 in from snout to tail, and weigh 1 kg. The largest living species of sea snail is Syrinx aruanus, its shell can measure up to 90 cm in length, and the whole animal with the shell can weigh up to 18 kg. The snail Lymnaea makes decisions by using two types of neuron, one deciding whether the snail is hungry, and the other deciding whether there is food in the vicinity. Named Gee Geronimo, this snail was owned by Christopher Hudson of Hove, East Sussex, UK, gastropods that lack a conspicuous shell are commonly called slugs rather than snails. Some species of slug have a red shell, some have only a vestige that serves mainly as a calcium repository. Other than that there is little difference between slugs and snails. There are however important differences in habitats and behavior, slugs squeeze themselves into confined spaces such as under loose bark on trees or under stone slabs, logs or wooden boards lying on the ground. In such retreats they are in danger from either predators or desiccation. Slugs as a group are far from monophyletic, biologically speaking slug is a term of convenience with little taxonomic significance, the reduction or loss of the shell has evolved many times independently within several very different lineages of gastropods
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Multicellular organism
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Multicellular organisms are organisms that consist of more than one cell, in contrast to unicellular organisms. Multicellular organisms arise in different ways, for example by cell division or by aggregation of many single cells. Colonial organisms are the result of identical individuals joining together to form a colony. Multicellularity has evolved independently at least 46 times, including in some prokaryotes, like cyanobacteria, myxobacteria, actinomycetes, however, complex multicellular organisms evolved only in six eukaryotic groups, animals, fungi, brown algae, red algae, green algae, and land plants. It evolved repeatedly for Chloroplastida, once or twice for animals, once for brown algae, the first evidence of multicellularity is from cyanobacteria-like organisms that lived 3–3.5 billion years ago. To reproduce, true multicellular organisms must solve the problem of regenerating a whole organism from germ cells, animals have evolved a considerable diversity of cell types in a multicellular body, compared with 10–20 in plants and fungi. Loss of multicellularity occurred in some groups, fungi are predominantly multicellular, though early diverging lineages are largely unicellular and there have been numerous reversions to unicellularity across fungi. It may also have occurred in some red algae, but it is possible that they are primitively unicellular), loss of multicellularity is also considered probable in some green algae. In other groups, generally parasites, a reduction of multicellularity occurred, multicellular organisms, especially long-living animals, face the challenge of cancer, which occurs when cells fail to regulate their growth within the normal program of development. Changes in tissue morphology can be observed during this process, cancer in animals has often been described as a loss of multicellularity. There is a discussion about the possibility of existence of cancer in other organisms or even in protozoa. For example, plant galls have been characterized as tumors but some argue that plants do not develop cancer. In some multicellular groups, which are called Weismannists, a separation between a sterile somatic cell line and a cell line evolved. However, Weismannist development is relatively rare, as part of species have the capacity for somatic embryogenesis. One hypothesis for the origin of multicellularity is that a group of function-specific cells aggregated into a mass called a grex. This is essentially what slime molds do, another hypothesis is that a primitive cell underwent nucleus division, thereby becoming a coenocyte. A membrane would then form around each nucleus, thereby resulting in a group of connected cells in one organism and this is what plant and animal embryos do as well as colonial choanoflagellates. Because the first multicellular organisms were simple, soft organisms lacking bone, shell or other body parts
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Symmetry in biology
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Symmetry in biology is the balanced distribution of duplicate body parts or shapes within the body of an organism. In nature and biology, symmetry is always approximate, for example plant leaves, while considered symmetrical, symmetry creates a class of patterns in nature, where the near-repetition of the pattern element is by reflection or rotation. The body plans of most multicellular organisms exhibit some form of symmetry, whether radial, bilateral, a small minority, notably among the sponges, exhibit no symmetry. Radially symmetric organisms resemble a pie where several cutting planes produce roughly identical pieces, such an organism exhibits no left or right sides. They have a top and a surface only. Most radially symmetric animals are symmetrical about an axis extending from the center of the oral surface, radial symmetry is especially suitable for sessile animals such as the sea anemone, floating animals such as jellyfish, and slow moving organisms such as starfish. Animals in the phyla cnidaria and echinodermata are radially symmetric, although many sea anemones and some corals have bilateral symmetry defined by a single structure, many flowers are radially symmetric or actinomorphic. Roughly identical flower parts – petals, sepals, and stamens occur at intervals around the axis of the flower. Many viruses have radial symmetries, their coats being composed of a small number of protein molecules arranged in a regular pattern to form polyhedrons, spheres. Tetramerism is a variant of radial symmetry found in jellyfish, which have four canals in an otherwise radial body plan, pentamerism, another variant of radial symmetry, means the organism is in five parts around a central axis, 72° apart. Among animals, only the echinoderms such as sea stars, sea urchins, being bilaterian animals, however, they initially develop with mirror symmetry as larvae, then gain pentaradial symmetry later. Flowering plants show fivefold symmetry in many flowers and in various fruits and this is well seen in the arrangement of the five carpels in an apple cut transversely. Hexamerism is found in the corals and sea anemones which are divided into two based on their symmetry. The most common corals in the subclass Hexacorallia have a body plan, their polyps have sixfold internal symmetry. Octamerism is found in corals of the subclass Octocorallia and these have polyps with eight tentacles and octameric radial symmetry. The octopus, however, has symmetry, despite its eight arms. Spherical symmetry occurs in an if it is able to be cut into two identical halves through any cut that runs through the organisms center. Organisms which show approximate spherical symmetry include the green alga Volvox
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