1.
Papilio xuthus
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It was also recorded in the state of Arunachal Pradesh, India, in 2014. It mates multiple times in its life, leading to a genetic diversity in its young. It is preyed upon by a host of organisms, including the tree cricket Oecanthus longicauda, ant Lasius niger, P. xuthus utilizes color vision and color constancy while foraging for plants of the family Rutaceae. It is common and not threatened, Papilio xuthus is common in urban, suburban, woods and orange orchards. The flight period is from May to August, males use both physical and visual cues to attract mates during the breeding season. Females of the species regularly mate with multiple partners, after mating, females use habitat and food quality to determine where they will oviposit their eggs. Papilio xuthus is a member of the Papilio genus, of which Papilio appalachiensis, Papilio canadensis and it is of the family Papilionidae and order Lepidoptera. It was first introduced in Hawaii in 1971 from Japan or Guam, P. xuthus makes significant seasonal migrations over 200 km. There are two subspecies of P. xuthus, Papilio xuthus koxingus and Papilio xuthus neoxuthus, the Asian swallowtail is a mid-sized, yellow, prominently-tailed butterfly. It has a wingspan of 45 to 55 mm and its normal color pattern consists of a black pattern on a yellow background. Wing coloration is sexually dimorphic, with females showing broader proximal marginal bands in the hindwing, blue-iridesecent and orange scales separate the black bands on the hindwing. The black bands also run in stripes of varying thickness along the forewing, the young caterpillar mimics bird feces and has a white and brown spot on its head. As they mature, caterpillars develop a green body color with brown spots. During the mating season, Asian swallowtail males fly through the foliage of trees in search of a mate. If a male encounters a female resting on a plant with open and horizontal wings, it approaches her, in addition, males use visual cues to conduct the mating ritual and are particularly attracted to closely spaced yellow patches on female wings. Most females of the Asian swallowtail butterfly mate more than once in their life and this behavior is typical of many other swallowtail butterflies including P. glaucus, P. helenus and P. protenor. By mating multiply, females are able to increase the diversity of their offspring. In addition, multiple matings allow females to produce a number of eggs
2.
Butterfly
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Butterflies are insects in the macrolepidopteran clade Rhopalocera from the order Lepidoptera, which also includes moths. Adult butterflies have large, often brightly coloured wings, and conspicuous, the group comprises the large superfamily Papilionoidea, which contains at least one former group, the skippers and the most recent analyses suggest it also contains the moth-butterflies. Butterfly fossils date to the Paleocene, which was about 56 million years ago, Butterflies have the typical four-stage insect life cycle. Winged adults lay eggs on the plant on which their larvae, known as caterpillars. The caterpillars grow, sometimes rapidly, and when fully developed. When metamorphosis is complete, the skin splits, the adult insect climbs out. Butterflies are often polymorphic, and many species use of camouflage, mimicry. Some, like the monarch and the lady, migrate over long distances. Many butterflies are attacked by parasites or parasitoids, including wasps, protozoans, flies, some species are pests because in their larval stages they can damage domestic crops or trees, other species are agents of pollination of some plants. Larvae of a few butterflies eat harmful insects, and a few are predators of ants, culturally, butterflies are a popular motif in the visual and literary arts. The Oxford English Dictionary derives the word straightforwardly from Old English butorflēoge, butter-fly, similar names in Old Dutch, the earliest Lepidoptera fossils are of a small moth, Archaeolepis mane, of Jurassic age, around 190 million years ago. Butterflies evolved from moths, so while the butterflies are monophyletic, the oldest butterflies are from the Palaeocene MoClay or Fur Formation of Denmark. The oldest American butterfly is the Late Eocene Prodryas persephone from the Florissant Fossil Beds, traditionally, the butterflies have been divided into the superfamily Papilionoidea excluding the smaller groups of the Hesperiidae and the more moth-like Hedylidae of America. Butterfly adults are characterized by their four scale-covered wings, which give the Lepidoptera their name, as in all insects, the body is divided into three sections, the head, thorax, and abdomen. The thorax is composed of three segments, each with a pair of legs, in most families of butterfly the antennae are clubbed, unlike those of moths which may be threadlike or feathery. The long proboscis can be coiled when not in use for sipping nectar from flowers, some day-flying moths, such as the hummingbird hawk-moth, are exceptions to these rules. Butterfly larvae, caterpillars, have a head with strong mandibles used for cutting their food. They have cylindrical bodies, with ten segments to the abdomen, generally with short prolegs on segments 3–6 and 10, many are well camouflaged, others are aposematic with bright colours and bristly projections containing toxic chemicals obtained from their food plants
3.
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
4.
Metamorphosis
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Metamorphosis is iodothyronine-induced and an ancestral feature of all chordates. Some insects, fishes, amphibians, mollusks, crustaceans, cnidarians, echinoderms, and tunicates undergo metamorphosis, animals that go through metamorphosis are called metamorphoses. Animals can be divided into species that undergo metamorphosis, incomplete metamorphosis. Scientific usage of the term is technically precise, and it is not applied to general aspects of cell growth, the word metamorphosis derives from Greek μεταμόρφωσις, transformation, transforming, from μετα-, change and μορφή, form. Metamorphosis is iodothyronine-induced and a feature of all chordates. In insects growth and metamorphosis are controlled by hormones synthesized by endocrine glands near the front of the body, neurosecretory cells in an insects brain secrete a hormone, the prothoracicotropic hormone that activates prothoracic glands, which secrete a second hormone, usually ecdysone, that induces ecdysis. PTTH also stimulates the corpora allata, an organ, to produce juvenile hormone. Experiments on firebugs have shown how juvenile hormone can affect the number of nymph instar stages in hemimetabolous insects, All three categories can be found in the diversity of insects, including no metamorphosis, incomplete or partial metamorphosis, and complete metamorphosis. In hemimetabolous insects, immature stages are called nymphs, development proceeds in repeated stages of growth and ecdysis, these stages are called instars. The juvenile forms closely resemble adults, but are smaller and lack features such as wings. The size and morphological differences between nymphs in different instars are small, often just differences in proportions and the number of segments, in later instars. In holometabolous insects, immature stages are called larvae, and differ markedly from adults, insects which undergo holometabolism pass through a larval stage, then enter an inactive state called pupa, and finally emerge as adults. The earliest insect forms showed direct development, and the evolution of metamorphosis in insects is thought to have fuelled their dramatic radiation, some early ametabolous true insects are still present today, such as bristletails and silverfish. Hemimetabolous insects include cockroaches, grasshoppers, dragonflies, and true bugs, phylogenetically, all insects in the Pterygota undergo a marked change in form, texture and physical appearance from immature stage to adult. According to research from 2008, adult Manduca sexta is able to retain behavior learned as a caterpillar, many observations have indicated that programmed cell death plays a considerable role during physiological processes of multicellular organisms, particularly during embryogenesis and metamorphosis. Sequence illustrating complete metamorphosis in the white butterfly, Pieris rapae In typical amphibian development, eggs are laid in water. Frogs, toads, and newts all hatch from the eggs as larvae with external gills, afterwards, newt larvae start a predatory lifestyle, while tadpoles mostly scrape food off surfaces with their horny tooth ridges. Metamorphosis in amphibians is regulated by thyroxin concentration in the blood, which stimulates metamorphosis, and prolactin, specific events are dependent on threshold values for different tissues
5.
Adult
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Biologically, an adult is a human or other organism that has reached sexual maturity. In human context, the term adult additionally has meanings associated with social and legal concepts, in contrast to a minor, a legal adult is a person who has attained the age of majority and is therefore regarded as independent, self-sufficient, and responsible. Human adulthood encompasses psychological adult development, conversely, one may legally be an adult but possess none of the maturity and responsibility that may define an adult character. In different cultures there are events that relate passing from being a child to becoming an adult or coming of age. This often encompasses the passing a series of tests to demonstrate that a person is prepared for adulthood, or reaching a specified age, most modern societies determine legal adulthood based on reaching a legally specified age without requiring a demonstration of physical maturity or preparation for adulthood. Historically and cross-culturally, adulthood has been determined primarily by the start of puberty, in the past, a person usually moved from the status of child directly to the status of adult, often with this shift being marked by some type of coming-of-age test or ceremony. After the social construct of adolescence was created, adulthood split into two forms, biological adulthood and social adulthood, thus, there are now two primary forms of adults, biological adults and social adults. Depending on the context, adult can indicate either definition, thus, the base definition of the word adult is the period beginning at puberty. Puberty generally begins around 10 or 11 years of age for girls and 11 or 12 years of age for boys, legally, adulthood means that one can engage in a contract. One can distinguish the legality of acts of a person, or of enabling a young person to carry out that act, by selling, renting out, showing, permitting entrance, allowing participation. There may be distinction between commercially and socially enabling, sometimes there is the requirement of supervision by a legal guardian, or just by an adult. Sometimes there is no requirement, but rather a recommendation, with regard to films with violence, etc. Some cultures in Africa define adulthood at age 13, according to Jewish tradition, adulthood is reached at age 13 for Jewish boys and girls, they are expected to demonstrate preparation for adulthood by learning the Torah and other Jewish practices. The Christian Bible and Jewish scripture contain no age requirement for adulthood or marrying, which includes engaging in sexual activity. The 1983 Code of Canon Law states, A man before he has completed his year of age
6.
Developmental biology
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Developmental biology is the study of the process by which animals and plants grow and develop. Developmental biology also encompasses the biology of regeneration, asexual reproduction and metamorphosis and in the growth, regional specification refers to the processes that create spatial pattern in a ball or sheet of initially similar cells. This generally involves the action of cytoplasmic determinants, located within parts of the fertilized egg, the early stages of regional specification do not generate functional differentiated cells, but cell populations committed to develop to a specific region or part of the organism. These are defined by the expression of combinations of transcription factors. Morphogenesis relates to the formation of three-dimensional shape and it mainly involves the orchestrated movements of cell sheets and of individual cells. Morphogenesis is important for creating the three layers of the early embryo and for building up complex structures during organ development. Cell differentiation relates specifically to the formation of cell types such as nerve, muscle. Differentiated cells contain large amounts of proteins associated with the cell function. Growth involves both an increase in size, and also the differential growth of parts which contributes to morphogenesis. Growth mostly occurs through cell division but also changes of cell size. The control of timing of events and the integration of the processes with one another is the least well understood area of the subject. It remains unclear whether animal embryos contain a master clock mechanism or not, the development of plants involves similar processes to that of animals. However plant cells are mostly immotile so morphogenesis is achieved by differential growth, also, the inductive signals and the genes involved in plant development are different from those that control animal development. Cell differentiation is the process whereby different functional cell types arise in development, for example, neurons, muscle fibers and hepatocytes are well known types of differentiated cell. The genes encoding these proteins are highly active, for example, NeuroD is a key transcription factor for neuronal differentiation, myogenin for muscle differentiation, and HNF4 for hepatocyte differentiation. Cell differentiation is usually the final stage of development, preceded by several states of commitment which are not visibly differentiated, a single tissue, formed from a single type of progenitor cell or stem cell, often consists of several differentiated cell types. Control of their formation involves a process of inhibition, based on the properties of the Notch signaling pathway. For example, in the plate of the embryo this system operates to generate a population of neuronal precursor cells in which NeuroD is highly expressed
7.
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
8.
Amphibian
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Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. They inhabit a variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic ecosystems. Thus amphibians typically start out as larvae living in water, the young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a respiratory surface and some small terrestrial salamanders and frogs lack lungs. They are superficially similar to lizards but, along with mammals and birds, reptiles are amniotes, the earliest amphibians evolved in the Devonian period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. They diversified and became dominant during the Carboniferous and Permian periods, over time, amphibians shrank in size and decreased in diversity, leaving only the modern subclass Lissamphibia. The three modern orders of amphibians are Anura, Urodela, and Apoda, the number of known amphibian species is approximately 7,000, of which nearly 90% are frogs. The smallest amphibian in the world is a frog from New Guinea with a length of just 7.7 mm. The largest living amphibian is the 1.8 m Chinese giant salamander, the study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology. The word amphibian is derived from the Ancient Greek term ἀμφίβιος, the term was initially used as a general adjective for animals that could live on land or in water, including seals and otters. Traditionally, the class Amphibia includes all tetrapod vertebrates that are not amniotes, the numbers of species cited above follows Frost and the total number of known amphibian species is over 7,000, of which nearly 90% are frogs. With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a group without unique defining features apart from shared primitive characteristics. Classification varies according to the phylogeny of the author and whether they use a stem-based or a node-based classification. The phylogeny of Paleozoic amphibians is uncertain, and Lissamphibia may possibly fall within groups, like the Temnospondyli or the Lepospondyli. If the common ancestor of amphibians and amniotes is included in Amphibia, all modern amphibians are included in the subclass Lissamphibia, which is usually considered a clade, a group of species that have evolved from a common ancestor. The three modern orders are Anura, Caudata, and Gymnophiona, although the fossils of several older proto-frogs with primitive characteristics are known, the oldest true frog is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona. It is anatomically similar to modern frogs. The oldest known caecilian is another Early Jurassic species, Eocaecilia micropodia, the earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China
9.
Cnidaria
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Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic environments, they are predominantly marine species. Their distinguishing feature is cnidocytes, specialized cells that use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are one cell thick. They have two basic forms, swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single orifice and body cavity that are used for digestion and respiration, many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both. Cnidarians activities are coordinated by a nerve net and simple receptors. Several free-swimming species of Cubozoa and Scyphozoa possess balance-sensing statocysts, not all cnidarians reproduce sexually, with many species having complex life cycles of asexual polyp stages and sexual medusae. Some, however, omit either the polyp or the medusa stage, Cnidarians were formerly grouped with ctenophores in the phylum Coelenterata, but increasing awareness of their differences caused them to be placed in separate phyla. Staurozoa have recently been recognised as a class in their own rather than a sub-group of Scyphozoa. Most cnidarians prey on organisms ranging in size from plankton to animals several times larger than themselves, but many obtain much of their nutrition from dinoflagellates, many are preyed on by other animals including starfish, sea slugs, fish and turtles. Many scleractinian corals—which form the foundation for coral reefs—possess polyps that are filled with zooxanthellae. While reef-forming corals are almost entirely restricted to warm and shallow waters, other cnidarians can be found at great depths, in polar regions. Recent phylogenetic analyses support monophyly of cnidarians, as well as the position of cnidarians as the group of bilaterians. Cnidarians form a phylum that are more complex than sponges, about as complex as ctenophores, and less complex than bilaterians. Cnidarians are distinguished from all other animals by having cnidocytes that fire like harpoons and are used mainly to capture prey, in some species, cnidocytes can also be used as anchors. Hence, cnidarians and ctenophores have traditionally been labelled diploblastic, along with sponges, however, both cnidarians and ctenophores have a type of muscle that, in more complex animals, arises from the middle cell layer. As a result, some recent text books classify ctenophores as triploblastic, adult cnidarians appear as either swimming medusae or sessile polyps, and many hydrozoan species are known to alternate between the two forms. Both are radially symmetrical, like a wheel and a tube respectively, since these animals have no heads, their ends are described as oral and aboral
10.
Biological life cycle
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In biology, a biological life cycle is a series of changes in form that an organism undergoes, returning to the starting state. The concept is related to those of the life history, development and ontogeny. Transitions of form may involve growth, asexual reproduction, and/or sexual reproduction, in some organisms, different generations of the species succeed each other during the life cycle. For plants and many algae, there are two stages, and the life cycle is referred to as alternation of generations. The term life history is used, particularly for organisms such as the red algae which have three multicellular stages, rather than two. Life cycles that include sexual reproduction involve alternating haploid and diploid stages, to return from a diploid stage to a haploid stage, meiosis must occur. In regard to changes of ploidy, there are 3 types of cycles, haplontic life cycle — the haploid stage is multicellular, diplontic life cycle — the diploid stage is multicellular and haploid gametes are formed, meiosis is gametic. Haplodiplontic life cycle — multicellular diploid and haploid stages occur, meiosis is sporic, the cycles differ in when mitosis occurs. Zygotic meiosis and gametic meiosis have one stage, mitosis occurs during the n phase in zygotic meiosis. Therefore, zygotic and gametic meiosis are collectively termed haplobiontic, sporic meiosis, on the other hand, has mitosis in two stages, both the diploid and haploid stages, termed diplobiontic. The study of reproduction and development in organisms was carried out by botanists and zoologists. Wilhelm Hofmeister demonstrated that alternation of generations is a feature that unites plants, some terms used for the description of life cycles were proposed initially for algae by Nils Svedelius, and then became used for other organisms. Other terms used in protist life cycles were introduced by Karl Gottlieb Grell, the description of the complex life cycles of various organisms contributed to the disproof of the ideas of spontaneous generation in the 1840s and 1850s. A zygotic meiosis is a meiosis of a zygote immediately after karyogamy and this way, the organism ends its diploid phase and produces several haploid cells. These cells divide mitotically to form larger, multicellular individuals. Two opposite types of gametes from these individuals or cells fuse to become a zygote, in the whole cycle, zygotes are the only diploid cell, mitosis occurs only in the haploid phase. The individuals or cells as a result of mitosis are haplonts, haplonts are, In archaeplastidans, some green algae In stramenopiles, some golden algae In alveolates, many dinoflagellates eg. Cells from the individuals then undergo meiosis to produce haploid cells or gametes
11.
Caterpillar
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Caterpillars /ˈkætərˌpɪlər/ are the larval stage of members of the order Lepidoptera. As with most common names, the application of the word is arbitrary, caterpillars of most species are herbivorous, but not all, some are insectivorous, even cannibalistic. Some feed on other products, for example clothes moths feed on wool. Caterpillars as a rule are voracious feeders and many of them are among the most serious of agricultural pests. In fact many moth species are best known in their caterpillar stages because of the damage cause to fruits and other agricultural produce, whereas the moths are obscure. Conversely, various species of caterpillar are valued as sources of silk, as human or animal food, the origins of the word caterpillar date from the early 16th century. They derive from Middle English catirpel, catirpeller, probably an alteration of Old North French catepelose, cate, cat + pelose, caterpillars have soft bodies that can grow rapidly between moults. Only the head capsule is hardened, the mandibles are tough and sharp for chewing leaves. Behind the mandibles of the caterpillar are the spinnerets, for manipulating silk, antennae are present on either side of the labrum, but small and relatively inconspicuous. Some larvae of the Hymenoptera order can appear like the caterpillars of the Lepidoptera, such larvae are mainly seen in the sawfly family. Caterpillars can be confused with the larvae of sawflies, lepidopteran larvae can be differentiated by, the numbers of pairs of pro-legs, sawfly larvae have 6 while caterpillars have up to 5 pairs. The number of stemmata, the larvae have only two, while a caterpillar has six. The presence of crochets on the prolegs, these are absent in the Symphyta, sawfly larvae have an invariably smooth head capsule with no cleavage lines, while lepidopterous caterpillars bear an inverted Y or V. Many animals feed on caterpillars as they are rich in protein, as a result, caterpillars have evolved various means of defense. The appearance of a caterpillar can often repel a predator, its markings and certain body parts can make it seem poisonous, or bigger in size and thus threatening, some types of caterpillars are indeed poisonous. Caterpillars have evolved defenses against physical conditions such as cold, hot or dry environmental conditions, some Arctic species like Gynaephora groenlandica have special basking and aggregation behaviours apart from physiological adaptations to remain in a dormant state. Many caterpillars are cryptically colored and resemble the plants on which they feed and they may even have parts that mimic plant parts such as thorns. Their size varies from as little as 1 mm to about 75 millimetres, some look like objects in the environment such as bird droppings
12.
Tadpole
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A tadpole is the larval stage in the life cycle of an amphibian, particularly that of a frog or toad. They are usually wholly aquatic, though some species have tadpoles that are terrestrial, when first hatched from the egg they have a more or less globular body, a laterally compressed tail and internal or external gills. As they grow they undergo metamorphosis, during which process they grow limbs, develop lungs, most tadpoles are herbivorous and during metamorphosis the mouth and internal organs are rearranged to prepare for an adult carnivorous lifestyle. Having no hard parts, it might be expected that fossil tadpoles would not exist, however, traces of biofilms have been preserved and fossil tadpoles have been found dating back to the Miocene. Tadpoles are eaten in parts of the world and are mentioned in folk tales. The name tadpole is from Middle English taddepol, made up of the elements tadde, toad, similarly, pollywog / polliwog is from Middle English polwygle, made up of the same pol, head, and wiglen, to wiggle. Tadpoles are young amphibians that live in the water, though a few tadpoles are semi-terrestrial and terrestrial. During the tadpole stage of the life cycle, most respire by means of autonomous external or internal gills. They do not usually have arms or legs until the transition to adulthood, as a tadpole matures, it most commonly metamorphosizes by gradually growing limbs and then outwardly absorbing its tail by apoptosis. Lungs develop around the time of leg development, and tadpoles late in development will often be found near the surface of the water, where they breathe air. During the final stages of external metamorphosis, the mouth changes from a small. The intestines shorten to accommodate the new diet, most tadpoles are herbivorous, subsisting on algae and plants. Some species are omnivorous, eating detritus and, when available, tadpoles vary greatly in size, both during their development and between species. For example, in a family, Megophryidae, length of late-stage tadpoles varies between 33 millimetres and 106 millimetres. The tadpoles of Pseudis paradoxa grow to 25 centimetres, the largest of any frog, despite their soft-bodied nature and lack of mineralised hard parts, fossil tadpoles have been recovered from Upper Miocene strata. They are preserved by virtue of biofilms, with more robust structures preserved as a carbon film, in Miocene fossils from Libros, Spain, the brain case is preserved in calcium carbonate, and the nerve cord in calcium phosphate. Other parts of the tadpoles bodies exist as organic remains and bacterial biofilms, tadpole remains with telltale external gills are also known from several of the Labyrinthodont groups. Some tadpoles are used as food, tadpoles of megophryid frog Oreolalax rhodostigmatus are particularly large, more than 10 cm in length, and are collected for human consumption in China
13.
Frog
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A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura. The oldest fossil proto-frog appeared in the early Triassic of Madagascar, Frogs are widely distributed, ranging from the tropics to subarctic regions, but the greatest concentration of species diversity is in tropical rainforests. There are approximately 4,800 recorded species, accounting for over 85% of extant amphibian species and they are also one of the five most diverse vertebrate orders. The body plan of a frog is generally characterized by a stout body, protruding eyes, cleft tongue, limbs folded underneath. Besides living in water and on dry land, the adults of some species are adapted for living underground or in trees. The skin of the frog is glandular, with secretions ranging from distasteful to toxic, Frogs skins vary in colour from well-camouflaged dappled brown, grey and green to vivid patterns of bright red or yellow and black to advertise toxicity and warn off predators. Frogs typically lay their eggs in water, the eggs hatch into aquatic larvae called tadpoles that have tails and internal gills. They have highly specialized rasping mouth parts suitable for herbivorous, omnivorous or planktivorous diets, the life cycle is completed when they metamorphose into adults. A few species deposit eggs on land or bypass the tadpole stage, adult frogs generally have a carnivorous diet consisting of small invertebrates, but omnivorous species exist and a few feed on fruit. Frogs are extremely efficient at converting what they eat into body mass and they are an important food source for predators and part of the food web dynamics of many of the worlds ecosystems. The skin is semi-permeable, making them susceptible to dehydration, so they live in moist places or have special adaptations to deal with dry habitats. Frogs are valued as food by humans and also have many roles in literature, symbolism. Frog populations have declined significantly since the 1950s, more than one third of species are considered to be threatened with extinction and over one hundred and twenty are believed to have become extinct since the 1980s. The number of malformations among frogs is on the rise and a fungal disease. Conservation biologists are working to understand the causes of these problems, the name frog derives from Old English frogga, abbreviated to frox, forsc, and frosc, probably deriving from Proto-Indo-European preu = to jump. About 88% of amphibian species are classified in the order Anura and these include around 4,810 species in 33 families, of which the Leptodactylidae, Hylidae and Ranidae are the richest in species. The use of the common frog and toad has no taxonomic justification. From a classification perspective, all members of the order Anura are frogs, there are numerous exceptions to this rule
14.
Barnacle
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A barnacle is a type of arthropod constituting the infraclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters and they are sessile suspension feeders, and have two nektonic larval stages. Around 1,220 barnacle species are currently known, the name Cirripedia is Latin, meaning curl-footed. Barnacles are encrusters, attaching themselves permanently to a hard substrate, the most common, acorn barnacles, are sessile, growing their shells directly onto the substrate. The order Pedunculata attach themselves by means of a stalk, free-living barnacles are attached to the substratum by cement glands that form the base of the first pair of antennae, in effect, the animal is fixed upside down by means of its forehead. In some barnacles, the cement glands are fixed to a long, muscular stalk, a ring of plates surrounds the body, homologous with the carapace of other crustaceans. These consist of the rostrum, two plates, two carinolaterals, and a carina. In sessile barnacles, the apex of the ring of plates is covered by an operculum, the plates are held together by various means, depending on species, in some cases being solidly fused. Inside the carapace, the lies on its back, with its limbs projecting upwards. Segmentation is usually indistinct, and the body is more or less divided between the head and thorax, with little, if any, abdomen. Adult barnacles have few appendages on their heads, with only a single, vestigial pair of antennae, attached to the cement gland. The six pairs of limbs are referred to as cirri. Barnacles have no heart, although a sinus close to the esophagus performs similar function. The blood vascular system is minimal, similarly, they have no gills, absorbing oxygen from the water through their limbs and the inner membrane of their carapaces. The excretory organs of barnacles are maxillary glands, the main sense of barnacles appears to be touch, with the hairs on the limbs being especially sensitive. The adult also has an eye, although this is probably only capable of sensing the difference between light and dark. This eye is derived from the naupliar eye. Barnacles have two larval stages, the nauplius and the cyprid, before developing into a mature adult
15.
Hymenoptera
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Hymenoptera is the third-largest order of insects, comprising the sawflies, wasps, bees, and ants. Over 150,000 species are recognized, with many more remaining to be described, females typically have a special ovipositor for inserting eggs into hosts or otherwise inaccessible places. The ovipositor is modified into a stinger. The young develop through holometabolism —that is, they have a larval stage. The name Hymenoptera refers to the wings of the insects, all references agree that the derivation involves the Ancient Greek πτερόν for wing. The Ancient Greek ὑμήν for membrane provides an etymology for the term because this order like several others has membranous wings. However, a key characteristic of this order is that the wings are connected to the fore wings by a series of hooks. Thus, another plausible etymology involves Hymen, the Ancient Greek god of marriage, Hymenoptera originated in the Triassic, with the oldest fossils belonging to the family Xyelidae. Social hymenopterans appeared during the Cretaceous, the evolution of this group has been intensively studied by Alex Rasnitsyn, Michael S. Engel, G. Dlussky, and others. This clade has been studied by examining the mitochondrial DNA, although this study was unable to resolve all the ambiguities in this clade, some relationships could be established. The Aculeata, Ichneumonomorpha, and Proctotrupomorpha were monophyletic, the Megalyroidea and Trigonalyoidea are sister clades as are the Chalcidoidea+Diaprioidea. The Cynipoidea was generally recovered as the group to Chalcidoidea and Diaprioidea which are each others closest relations. The cladogram is based on Schulmeister 2003, hymenopterans range in size from very small to large insects, and usually have two pairs of wings. Their mouthparts are adapted for chewing, with well-developed mandibles, many species have further developed the mouthparts into a lengthy proboscis, with which they can drink liquids, such as nectar. They have large eyes, and typically three simple eyes. The forward margin of the hind wing bears a number of hooked bristles, or hamuli, the smaller species may have only two or three hamuli on each side, but the largest wasps may have a considerable number, keeping the wings gripped together especially tightly. Hymenopteran wings have relatively few veins compared with other insects. In the more ancestral hymenopterans, the ovipositor is blade-like, and has evolved for slicing plant tissues, in the majority, however, it is modified for piercing, and, in some cases, is several times the length of the body
16.
Ropalidia marginata
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Ropalidia marginata is an Old World species of paper wasp. It is primitively eusocial, not showing the same bias in brood care seen in social insects with greater asymmetry in relatedness. The species employees a variety of colony founding strategies, sometimes with single founders, the queen does not use physical dominance to control workers, there is evidence of pheromones being used to suppress other female workers from overtaking queenship. R. marginata is an insect, having six legs and it is in the order Hymenoptera, containing wasps, ants and bees. It is in the family Vespidae, with wasps, yellow jackets and it is in the subfamily Polistinae, containing eusocial wasps and it is in the tribe Ropalidiini. On the Indian subcontinent, there are 22 recognized species of the genus Ropalidia, the species R. travancorica, once thought separate, was determined synonymous with R. marginata after intensive specimen comparisons in 1989. R. marginata is most closely related to R. spatulata, the male antenna and genitalia are similar between R. brevita and R. marginata. R. marginata are a reddish color, with yellow spots on some joints. Males differ from females by having a weaker mandible and lacking a stinger, the female workers are not morphologically different from the queen and are more distinguishable by behavior. Females are hard to distinguish morphologically except for their level of ovary development, females are the default workers of R. marginata, but they may also rise to queenship by taking over a resident queen, founding a new colony, or adopting an abandoned one. Female workers forage to feed themselves and non-foragers, such as the queen, larvae and they help to build the nest and care for the larvae. Workers may mate with males and remain inseminated even if they are never able to attain queenship, worker-worker relatedness is not asymmetrically higher than relatedness between workers and males or workers and the queen. This is because of overlapping matrilines and patrilines within the colony which decreases relatedness overall between individuals, when a queen is lost, a worker has the ability to take her place. The mechanism by which the next-in-line-queen is chosen is cryptic, neither age nor dominance accurately predicts the successor, the potential queen may or may not be inseminated or have developed ovaries. The only certainty is that after the queen is gone, the worker who is the queen will become very aggressive. The aggressiveness subsides after about two days, the potential queen seems to require this heightened aggression in order to boost her own development. Primitively eusocial societies are typically headed by behaviourally aggressive queens, who use aggression to suppress worker reproduction, however, the queen in R. marginata is a docile sitter who does not use physical aggression to maintain her reproductive monopoly in the colony. The queens are suspected to control workers through pheromones and she uses these pheromones to signal her presence and fecundity to her workers, who perceive these signals and refrain from reproducing
17.
Newt
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A newt is a salamander in the subfamily Pleurodelinae, also called eft during its terrestrial juvenile phase. Unlike other members of the family Salamandridae, newts are semiaquatic, not all aquatic salamanders are considered newts, however. The more than 100 known species of newts are found in North America, Europe, North Africa, newts metamorphose through three distinct developmental life stages, aquatic larva, terrestrial juvenile, and adult. Adult newts have lizard-like bodies and return to the every year to breed, otherwise living in humid. Newts are threatened by loss, fragmentation and pollution. Several species are endangered, and at least one species, the Yunnan lake newt, has gone extinct recently, the Old English name of the animal was efte, efeta, resulting in Middle English eft, this word was transformed irregularly into euft, evete, or ewt. The initial n was added from the article an by provection by the early 15th century. The form newt appears to have arisen as a variant of eft in Staffordshire. Dialectal English and Scots also has the word ask used for both newts and wall lizards, from Old English āþexe, from Proto-Germanic *agiþahsijǭ, literally lizard-badger or distaff-like lizard. Latin had the name stellio for a type of spotted newt, ancient Greek had the name κορδύλος, presumably for the water newt. German has Molch, from Middle High German mol, wikt, olm, newts are also known as Tritones in historical literature, and triton remains in use as common name in some Romance languages, in Greek, in Russian and Serbian. The systematic name Tritones was introduced alongside Pleurodelinae by Tschudi in 1838, laurentis Triton was renamed to Triturus by Rafinesque in 1815. Tschudis Pleurodelinae is based on the type genus Pleurodeles named by Michahelles in 1830, newts are found in North America, Europe, North Africa and Asia. Eastern Asia, from Eastern India over Indochina to Japan, is home to five genera with more than 40 species, newts are semi-aquatic, spending part of the year in the water for reproduction and the rest of the year on land. While most species prefer stagnant water bodies such as ponds, ditches or flooded meadows for reproduction, the European brook newts and European mountain newts have even adapted to life in cold, oxygen-rich mountain streams. During their terrestrial phase, newts live in habitats with abundandant cover such as logs, rocks. Newts share many of the characteristics of their kin, Caudata, including semipermeable glandular skin, four equal-sized limbs. The newts skin, however, is not as smooth as that of other salamanders, aquatic larvae have true teeth on both upper and lower jaws, and external gills
18.
Puberty
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Puberty is the process of physical changes through which a childs body matures into an adult body capable of sexual reproduction. It is initiated by signals from the brain to the gonads, the ovaries in a girl. In response to the signals, the gonads produce hormones that stimulate libido and the growth, function, and transformation of the brain, bones, muscle, blood, skin, hair, breasts, and sex organs. Physical growth—height and weight—accelerates in the first half of puberty and is completed when a body has been developed. Until the maturation of their capabilities, the pre-pubertal physical differences between boys and girls are the external sex organs. On average, girls begin puberty around ages 10–11, boys around ages 11–12, girls usually complete puberty around ages 15–17, while boys usually complete puberty around ages 16–17. In the 21st century, the age at which children, especially girls, reach puberty is lower compared to the 19th century. Puberty which starts earlier than usual is known as precocious puberty, Puberty which starts later than usual is known as delayed puberty. Two of the most significant differences between puberty in girls and puberty in boys are the age at which it begins, and the sex steroids involved, the testosterones. Although there is a range of normal ages, girls typically begin the process of puberty at age 10 or 11. Girls usually complete puberty by ages 15–17, while boys usually complete puberty by ages 16–17, girls attain reproductive maturity about four years after the first physical changes of puberty appear. In contrast, boys accelerate more slowly but continue to grow for about six years after the first visible pubertal changes, any increase in height beyond the post-pubertal age is uncommon. For boys, an androgen called testosterone is the sex hormone. While testosterone is produced, all changes are characterized as virilization. The conversion of testosterone to estradiol depends on the amount of body fat, the male growth spurt also begins later, accelerates more slowly, and lasts longer before the epiphyses fuse. Although boys are on average 2 centimetres shorter than girls before puberty begins, the hormone that dominates female development is an estrogen called estradiol. While estradiol promotes growth of the breasts and uterus, it is also the principal hormone driving the growth spurt and epiphyseal maturation. Estradiol levels rise earlier and reach higher levels in women than in men, the hormonal maturation of females is considerably more complicated than in boys
19.
Neoteny
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Neoteny (/niːˈɒtᵻni/ /niːˈɒtni/ or /niːˈɒtəni/, is the delaying or slowing of the physiological development of an organism, typically an animal. Neoteny is found in modern humans, in progenesis, sexual development is accelerated. Both neoteny and progenesis result in paedomorphism, a type of heterochrony, some authors define paedomorphism as the retention of larval traits, as seen in salamanders. Both neoteny and progenesis cause the retention in adults of traits seen only in the young. Such retention is important in biology, domestication, and evolutionary developmental biology. The origins of the concept of neoteny have been traced to the Bible, the word neoteny is borrowed from the German Neotenie, the latter constructed by Kollmann from the Greek νέος and τείνειν. The adjective is either neotenic or neotenous, for the opposite of neotenic, different authorities use either gerontomorphic or peramorphic. In 1926, Louis Bolk described neoteny as the process in humanization. Neoteny in humans is the slowing or delaying of body development, compared to non-human primates, resulting in such as a large head, a flat face. These neotenic changes may have brought about by sexual selection in human evolution. In turn, they may have permitted the development of human capacities such as emotional communication, however, humans also have relatively large noses and long legs, both peramorphic traits. Some evolutionary theorists have proposed that neoteny was a key feature in human evolution, stephen Jay Gould believed that the evolutionary story of humans is one where we have been retaining to adulthood the originally juvenile features of our ancestors. J. B. S. Haldane mirrors Goulds hypothesis by stating a major trend in human beings is greater prolongation of childhood. Delbert D. Thiessen said that neoteny becomes more apparent as early primates evolved into later forms, neoteny is seen in domesticated animals such as dogs and mice. This is because there are resources available, less competition for those resources. This allows them to mature and reproduce more quickly than their wild counterparts, the environment that domesticated animals are raised in determines whether or not neoteny is present in those animals. Evolutionary neoteny can arise in a species when those conditions occur, another explanation for the neoteny in domesticated animals can be the selection for certain behavioral characteristics. Behavior is linked to genetics which therefore means that when a trait is selected for
20.
Recapitulation theory
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Since embryos also evolve in different ways, the theory of recapitulation is seen as a historical side-note, rather than as dogma in the field of developmental biology. Recapitulation theory is considered plausible by some researchers in fields such as the study of the origin of language, cognitive development. The earliest recorded trace of a theory is from the Egyptian Pharaoh Psamtik I. The concept of recapitulation was first formulated outside the field of biology and it was widely held among traditional theories of the origin of language, being assumed as a premise that childrens use of language gives insights on its origin and evolution. The idea was reprised in 1720 by Giambattista Vico in his influential Scienza Nuova and it was first formulated in biology in the 1790s among the German Natural philosophers, after which, Marcel Danesi states, it soon gained the status of a supposed biogenetic law. The theory was first formalised by Étienne Serres in 1824–26, based on the work of Johann Friedrich Meckel and this attempted to link comparative embryology with a pattern of unification in the organic world. It was supported by Étienne Geoffroy Saint-Hilaire, and became a prominent part of his ideas and it suggested that past transformations of life could have been through environmental causes working on the embryo, rather than on the adult as in Lamarckism. These naturalistic ideas led to disagreements with Georges Cuvier, ernst Haeckel attempted to synthesize the ideas of Lamarckism and Goethes Naturphilosophie with Charles Darwins concepts. Since early in the century, Haeckels biogenetic law has been refuted on many fronts. Haeckel formulated his theory as Ontogeny recapitulates phylogeny, the notion later became simply known as the recapitulation theory. Ontogeny is the growth and development of an organism, phylogeny is the evolutionary history of a species. Haeckel claimed that the development of advanced species passes through stages represented by adult organisms of more primitive species, otherwise put, each successive stage in the development of an individual represents one of the adult forms that appeared in its evolutionary history. Embryonic pharyngeal slits, which form in animals when the thin branchial plates separating pharyngeal pouches and pharyngeal grooves perforate. Pharyngeal arches appear in all tetrapod embryos, in mammals, the first pharyngeal arch develops into the jaw, the malleus. But these embryonic pharyngeal arches, grooves, pouches, and slits in human embryos can not at any stage carry out the function as the gills of an adult fish. Haeckel produced several drawings that often overemphasized similarities between embryos of related species. The misinformation was propagated through many biology textbooks, and popular knowledge, Haeckels drawings were disputed by Wilhelm His, who had developed a rival theory of embryology. His developed a theory of human embryonic development
21.
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
22.
Dicyemida
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Rhombozoa, or Dicyemida, is a phylum of tiny parasites that live in the renal appendages of cephalopods. Although the name Dicyemida precedes Rhombozoa in usage, and is preferred by most contemporary authors, traditionally, dicyemids have been grouped with the Orthonectida in the Mesozoa, however, molecular phylogenies indicate that dicyemids may be more closely related to the roundworms. The phylum is not divided in classes, but contains three families, Conocyemidae, Dicyemidae, and Kantharellidae, molecular evidence suggests that this phylum are derived from the Lophotrochozoa. Adult dicyemids range in length from 0.5 to 7 millimetres and they display eutely, a condition in which each adult individual of a given species has the same number of cells, making cell number a useful identifying character. Dicyemida lack respiratory, circulatory, excretory, digestive, and nervous systems, the organisms structure is simple, a single axial cell is surrounded by a jacket of twenty to thirty ciliated cells. The anterior region of the organism is termed a calotte and functions to attach the parasite to folds on the surface of its hosts renal appendages, dicyemids exist in both asexual and sexual forms. The former predominate in juvenile and immature hosts, and the latter in mature hosts, the asexual stage is termed a nematogen, it produces vermiform larvae within the axial cell. These mature through direct development to form more nematogens, nematogens proliferate in young cephalopods, filling the kidneys. As the infection ages, perhaps as the nematogens reach a density, vermiform larvae mature to form rhombogens. This sort of density-responsive reproductive cycle is reminiscent of the reproduction of sporocysts or rediae in larval trematode infections of snails. As with the asexual stages, a few nematogens can usually be found in older hosts. Their function may be to increase the population of the parasite to keep up with the growth of the host, rhombogens contain hermaphroditic gonads developed within the axial cell. These gonads, more correctly termed infusorigens, self-fertilise to produce infusoriform larvae and these larvae possess a very distinctive morphology, swimming about with ciliated rings that resemble headlights. It has long assumed that this sexually produced infusoriform, which is released when the host eliminates urine from the kidneys, is both the dispersal and the infectious stage. The mechanism of infection, however, remains unknown, as are the effects, if any, some part of the dicyemid life cycle may be tied to temperate benthic environments, where they occur in greatest abundance. While dicyemids have occasionally found in the tropics, the infection rates are typically quite low. Dicyemids have never reported from truly oceanic cephalopods, who instead host a parasitic ciliate fauna. Most dicyemid species are recovered from one or two host species
23.
Ctenophora
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Ctenophora is a phylum of invertebrate animals that live in marine waters worldwide. Their most distinctive feature is the ‘combs’ – groups of cilia which they use for swimming – they are the largest animals that swim by means of cilia, adults of various species range from a few millimeters to 1.5 m in size. Like cnidarians, their bodies consist of a mass of jelly, with one layer of cells on the outside, in ctenophores, these layers are two cells deep, while those in cnidarians are only one cell deep. Some authors combined ctenophores and cnidarians in one phylum, Coelenterata, increasing awareness of the differences persuaded more recent authors to classify them as separate phyla. Ctenophores also resemble cnidarians in having a decentralized nerve net rather than a brain, genomic studies have suggested that the neurons of Ctenophora, which differ in many ways from other animal neurons, evolved independently from those of the other animals. In favorable circumstances, ctenophores can eat ten times their own weight in a day, only 100–150 species have been validated, and possibly another 25 have not been fully described and named. The textbook examples are cydippids with egg-shaped bodies and a pair of retractable tentacles fringed with tentilla that are covered with colloblasts, most species are hermaphrodites—a single animal can produce both eggs and sperm, meaning it can fertilize its own egg, not needing a mate. Some are simultaneous hermaphrodites, which can produce eggs and sperm at the same time. Others are sequential hermaphrodites, in which the eggs and sperm mature at different times, fertilization is generally external, although platyctenids eggs are fertilized inside their parents bodies and kept there until they hatch. The young are generally planktonic and in most species look like miniature cydippids, in at least some species, juveniles are capable of reproduction before reaching the adult size and shape. The combination of hermaphroditism and early reproduction enables small populations to grow at an explosive rate, ctenophores may be abundant during the summer months in some coastal locations, but in other places they are uncommon and difficult to find. The situation was aggravated by other factors, such as over-fishing, the later accidental introduction of Beroe helped to mitigate the problem, as Beroe preys on other ctenophores. Ctenophores form a phylum that is more complex than sponges, about as complex as cnidarians. Unlike sponges, both ctenophores and cnidarians have, cells bound by inter-cell connections and carpet-like basement membranes, muscles, nervous systems, ctenophores are distinguished from all other animals by having colloblasts, which are sticky and adhere to prey, although a few ctenophore species lack them. Hence ctenophores and cnidarians have traditionally been labelled diploblastic, along with sponges, ranging from about 1 millimeter to 1.5 meters in size, ctenophores are the largest non-colonial animals that use cilia as their main method of locomotion. The name ctenophora means comb-bearing, from the Greek κτείς meaning comb, for a phylum with relatively few species, ctenophores have a wide range of body plans. Coastal species need to be enough to withstand waves and swirling sediment particles. In addition oceanic species do not preserve well, and are mainly from photographs
24.
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
25.
Turbellaria
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The Turbellaria are one of the traditional sub-divisions of the phylum Platyhelminthes, and include all the sub-groups that are not exclusively parasitic. There are about 4,500 species, which range from 1 mm to large freshwater forms more than 500 mm long or terrestrial species like Bipalium kewense which can reach 600 mm in length, however, many of the smaller forms are round in cross section. Most are predators, and all live in water or in moist terrestrial environments, most forms reproduce sexually and with few exceptions all are simultaneous hermaphrodites. The Acoelomorpha and the genus Xenoturbella were formerly included in the Turbellaria, all the exclusively parasitic Platyhelminthes form a monophyletic group Neodermata, and it is agreed that these are descended from one small sub-group within the free-living Platyhelminthes. Hence the Turbellaria as traditionally defined are paraphyletic, traditional classifications divide the Platyhelminthes into four groups, Turbellaria and the wholly parasitic Trematoda, Monogenea and Cestoda. In this classification the Turbellaria include the Acoelomorpha, the name Turbellaria refers to the whirlpools of microscopic particles created close to the skins of aquatic species by the movement of their cilia. Like other bilaterians they are triploblastic, having three main cell layers. The radially symmetrical cnidarians and ctenophore are diploblastic having only two cell layers, unlike most other bilaterians, platyhelminthes have no internal body cavity and are therefore described as acoelomates. Hence many are microscopic and the species have flat ribbon-like or leaf-like shapes. The guts of large species have many branches, so that nutrients can 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. The gut is lined with a layer of endodermal cells which absorb. Some species break up and soften food first by secreting enzymes in the gut or the pharynx, all animals need to keep the concentration of dissolved substances in their body fluids at a fairly constant level. Despite this difference in environments, most platyhelminths use the system to control the level of concentration in their body fluids. These combinations of flame cells and tubule cells are called protonephredia, in all platyhelminths the nervous system is concentrated at the head end. Most species have rings of ganglia in the head and main nerve trunks running along their bodies, planarians are famous for their ability to regenerate if divided by cuts across their bodies. Experiments show that, in fragments that do not already have a head and this suggests that the growth of a head is controlled by a chemical whose concentration diminishes from head to tail. These have about 4,500 species, are mostly free-living, most are predators or scavengers, and terrestrial species are mostly nocturnal and live in shaded humid locations such as leaf litter or rotting wood. However some are symbiotes of animals such as crustaceans
26.
Trematoda
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Trematoda is a class within the phylum Platyhelminthes. It includes two groups of parasitic flatworms, known as flukes and they are internal parasites of molluscs and vertebrates. Most trematodes have a life cycle with at least two hosts. The primary host, where the flukes sexually reproduce, is a vertebrate, the intermediate host, in which asexual reproduction occurs, is usually a snail. The trematodes or flukes include 18,000 to 24,000 species, nearly all trematodes are parasites of mollusks and vertebrates. The smaller Aspidogastrea, comprising about 100 species, are parasites of mollusks and may also infect turtles and fish. The Digenea, the majority of trematodes, are parasites of both mollusks and vertebrates, but rarely occur in cartilaginous fish. Trematodes are flattened oval or worm-like animals, usually no more than a few centimetres in length, although species as small as 1 millimetre and as large as 7 centimetres are known. Their most distinctive feature is the presence of two suckers, one close to the mouth, and the other on the underside of the animal. The body surface of trematodes comprises a tough syncitial tegument, which protect against digestive enzymes in those species that inhabit the gut of larger animals. It is also the surface of gas exchange, there are no respiratory organs, the mouth is located at the forward end of the animal, and opens into a muscular, pumping pharynx. The pharynx connects, via a short oesophagus, to one or two blind-ending caeca, which occupy most of the length of the body, in some species, the caeca are themselves branched. As in other flatworms, there is no anus, and waste material must be egested through the mouth, although the excretion of nitrogenous waste occurs mostly through the tegument, trematodes do possess an excretory system, which is instead mainly concerned with osmoregulation. This consists of two or more protonephridia, with those on side of the body opening into a collecting duct. The two collecting ducts typically meet up at a single bladder, opening to the exterior through one or two pores near the end of the animal. The brain consists of a pair of ganglia in the head region, the nerve cords running along the ventral surface are always the largest, while the dorsal cords are present only in the Aspidogastrea. Trematodes generally lack any specialised sense organs, although some species do possess one or two pairs of simple ocelli. Most trematodes are simultaneous hermaphrodites, having male and female organs
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Trematode life cycle stages
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Trematodes or flukes are small parasitic flatworms that use vertebrates as their definitive host, and molluscs as their intermediate host. To accomplish this, they have varied life cycle stages. The life cycle of a typical digenean trematode can be thought to begin when its egg is immersed in water, following this, a miracidium hatches, which swims to find a mollusc host. The miracidia go through stages in the mollusc host, eventually emerging as motile cercarial larvae. The cercaria either infects vertebrates through the skin or is ingested, in its vertebrate host, the cercaria matures to an adult form, the fluke, and lays eggs that are discharged with the host feces or urine. In the presence of water, the eggs hatch and the miracidium stage of life is reached again. Sporocyst – an elongated sac, it produces either rediae or more sporocysts, redia – a larval form with an oral sucker, it will produce either more rediae, or cercariae. Cercaria – the larval form of the parasite, it develops within the cells of the sporocyst or redia. A cercaria has a head with large penetration glands. It may or may not have a long swimming tail, depending on the species, the motile cercaria finds and settles in a host where it will become either an adult, or a mesocercaria, or a metacercaria, according to species. Mesocercaria – a cercaria little modified but resting Metacercaria – a cercaria encysted and resting Adult – the fully developed mature stage, not all trematodes follow the typical sequence of eggs, miracidia, sporocysts, rediae, cercariae, and adults. In some species, the stage is omitted, and sporocysts produce cercariae. In some species, the cercaria develops into an adult within the same host, many digenean trematodes require two hosts, one where asexual reproduction occurs in sporocysts, the other a vertebrate where the adult form engages in sexual reproduction to produce eggs. In some species the cercaria encysts, and waits until the host is eaten by a third host, in whose gut it emerges, most trematodes are hermaphroditic, but members of the family Schistosomatidae are dioecious. Males are shorter and stouter than the females, bucephalus polymorphus Trematode infection Apicomplexa lifecycle stages Life cycle of Schistosoma mansoni
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Monogenea
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Monogenea are a group of largely ectoparasitic members of the flatworm phylum Platyhelminthes, class Monogenea. Monogenea are small parasitic flatworms mainly found on skin or gills of fish and they are rarely longer than about 2 cm. A few species infecting certain marine fish are larger and marine forms are larger than those found on fresh water hosts. Monogeneans lack respiratory, skeletal and circulatory systems and have no or weakly developed oral suckers, Monogenea attach to hosts using hooks, clamps and a variety of other specialized structures. They are often capable of dramatically elongating and shortening as they move, biologists need to ensure that specimens are completely relaxed before measurements are taken. Like all ectoparasites, monogeneans have well-developed attachment structures, the anterior structures are collectively termed the prohaptor, while the posterior ones are collectively termed the opisthaptor, or simply haptor. The posterior opisthaptor with its hooks, anchors, clamps etc. is typically the major attachment organ, like other flatworms, Monogenea have no true body cavity. They have a digestive system consisting of a mouth opening with a muscular pharynx. Generally, they also are hermaphroditic with functional reproductive organs of both sexes occurring in one individual, most species are oviparous but a few are viviparous. Monogenea are Platyhelminthes and therefore are among the lowest invertebrates to possess three embryonic germ layers—endoderm, mesoderm, and ectoderm, in addition, they have a head region that contains concentrated sense organs and nervous tissue. The ancestors of Monogenea were probably free-living flatworms similar to modern Turbellaria, according to the more widely accepted view, rhabdocoel turbellarians gave rise to monogeneans, these, in turn, gave rise to digeneans, from which the cestodes were derived. Another view is that the rhabdocoel ancestor gave rise to two lines, one gave rise to monogeneans, who rise to digeneans, and the other line gave rise to cestodes. There are about 50 families and thousands of described species and these groups are also known as Polyonchoinea and Heteronchoinea, respectively. Polyopisthocotyleans are almost exclusively gill-dwelling blood feeders, whereas Monopisthocotyleans may live on the gills, skin, monopisthocotylea include, Genus Gyrodactylus, which has no eyespots and is viviparous. Genus Dactylogyrus, which has four eyespots and is oviparous and this is one of the largest metazoan genera, with at least 970 species. Genus Neobenedenia, which is larger and lives on the skin of many tropical marine species. All of which can cause epizootics in freshwater fish when raised in aquaculture, polyopisthocotylea include, Genus Diclidophora, which is primarily found in marine fish and primitive freshwater fish like sturgeons and paddlefish. Genus Protopolystoma, found in aquatic clawed toads, monogeneans possess the simplest life cycle among the parasitic platyhelminths
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Cestoda
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Cestoda is a class of parasitic flatworms of the phylum Platyhelminthes. Biologists informally refer to them as cestodes, the best-known species are commonly called tapeworms. All cestodes are parasitic and their life histories vary, but typically they live in the tracts of vertebrates as adults. Over a thousand species have been described, and all species may be parasitised by at least one species of tapeworm. Humans are subject to infection by several species of tapeworms if they eat undercooked meat such as pork, beef, and fish, or if they live in, or eat food prepared in, conditions of poor hygiene. T. saginata, the tapeworm, can grow up to 20 m, the largest species. Species using small vertebrates as hosts, though, tend to be small, for example, vole and lemming tapeworms are only 13–240 mm in length, and those parasitizing shrews only 0. 8–60 mm. The worms scolex attaches to the intestine of the definitive host, in some species, the scolex is dominated by bothria, or sucking grooves that function like suction cups. Other species have hooks and suckers that aid in attachment, cyclophyllid cestodes can be identified by the presence of four suckers on their scolices. While the scolex is often the most distinctive part of a tapeworm, it is often unnoticed in a clinical setting. Therefore, identifying eggs and proglottids in feces is the simplest way to diagnose an infection, the main nerve centre of a cestode is a cerebral ganglion in its scolex. Motor and sensory innervation depends on the number of nerves in, smaller nerves emanate from the ganglion to supply the general body muscular and sensory ending. The cirrus and vagina are innervated, and sensory endings around the genital pore are more plentiful than other areas, sensory function includes both tactoreception and chemoreception. The body is composed of segments called proglottids. The sum of the proglottids is called a strobila, which is thin, from this is derived the common name tapeworm. Proglottids are continually produced by the region of the scolex, as long as the scolex is attached. Like some other flatworms, cestodes use flame cells, located in the proglottids, mature proglottids are released from the tapeworms end segment and leave the host in feces or migrate as independent motile proglottids. The proglottids farthest away from the scolex are the ones containing eggs
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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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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
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Microfilaria
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Microfilaria may also refer to an informal collective group genus name, proposed by Cobbold in 1882. While a convenient category for newly discovered microfilariae which can not be assigned to a species because the adults are unknown. The microfilaria is a stage in the life cycle of certain parasitic nematodes in the family Onchocercidae. In these species, the live in a tissue or the circulatory system of vertebrates. They release microfilariae into the bloodstream of the vertebrate host, the microfilariae are taken up by blood-feeding arthropod vectors. In the intermediate host the microfilariae develop into larvae that can be transmitted to a new vertebrate host. The presence of microfilariae in the host bloodstream is called microfilaraemia, the success of filariasis eradication programs is typically gauged by the reduction in numbers of circulating microfilariae in infested individuals within a geographic area. All parasites need a mechanism for spreading to new individual hosts, parasites in the lower gastrointestinal tract usually shed eggs in the host feces. Tissue-dwelling parasites, such as Trichinella spiralis, rely on new hosts eating the tissues of their current host and this system is seen in the life cycle of Elaeophora schneideri. The adults of E. schneideri typically reside in the artery of its definitive host. The female may be up to 12 cm long, and releases microfilariae which measure 207 by 13 µm into the bloodstream of the host. The blood flow carries the microfilariae away from the female in the carotid artery, because of their size, the microfilariae pass easily through successively smaller vessels, becoming physically lodged in the small capillaries near the skin surface of the face and head. Attracted by the carbon dioxide exhaled by the deer, the blood-feeding female horse fly often lands on the head or face to feed. The horse fly uses its scissor-like mouthparts to cut the surface of the skin, the microfilariae, which were just under the surface of the skin, are small enough to be ingested whole by the horse fly. Once inside the horse fly, the microfilariae bore through the stomach wall and these larvae migrate to the head and mouthparts of the horse fly, and enter the bloodstream of another vertebrate host when the horse fly feeds again. Most recent parasitology textbooks consider the microfilariae to be pre-larvae or advanced embryos which develop into the first stage larvae in the arthropod vector. Some consider them to be the first larval stage, such as microfilariae, in either case, the microfilaria is the stage which develops from the egg. In most tissue-dwelling species the eggs hatch in the uterus of the female, in most blood-dwelling species, embryonated eggs are released, and they will only exsheath after being ingested by the arthropod intermediate host
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Sipuncula
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The Sipuncula or Sipunculida is a group containing 144–320 species of bilaterally symmetrical, unsegmented marine worms. Sipuncula signifies little tube or siphon, traditionally considered a phylum, they might be a subgroup of phylum Annelida based on recent molecular work. The first species of this phylum was described in 1827 by the French zoologist Henri Marie Ducrotay de Blainville who named it Sipunculus vulgaris, a related species was later described as Golfingia macintoshii by E. Ray Lankester. The specimen was provided by a friend of his, Professor Mackintosh, the specimen was dissected by Lankester between rounds of golf at Saint Andrews golf club in Scotland from which the species derives its name. Golfingia is now the name and Sipuncula the name of the phylum to which these worms belong. They are relatively common in shallow waters, either in burrows or in discarded shells as hermit crabs do, Some bore into solid rocks to make a shelter for themselves. The sipunculan body is divided into a trunk and a narrower, retractable anterior section. The body wall surrounds the coelom that is filled with fluid on which the body wall musculature acts as a skeleton to extend or contract the animal. When threatened, Sipunculids can retract their body into a shape resembling a peanut kernel—a practice that has given rise to the name peanut worm. The introvert is retractable into the trunk via two pairs of muscles that extend as narrow ribbons from the trunk wall to attachment points in the introvert. The introvert can be protruded from the trunk by contracting the muscles of the trunk wall, the sipunculan mouth, located at the anterior end of the introvert, is surrounded by a mass of 18–24 ciliated tentacles in the Sipunculidea. In the Phascolosomatidea, the tentacles are arranged in an arc around the nuchal organ, the tentacles are used to gather organic detritus from the water or substrate, and probably also function as gills. In the family Themistidae the tentacles forms a crown, as the members of group are specialized filter feeders. Hooks are often present near the mouth on the introvert and these are proteinaceous, non-chitinous specializations of the epidermis, either arranged in rings or scattered. Three genera possess epidermal modifications, called the anal shield near the anteriorly located anus on the trunk just below the introvert of the animal. In Aspidosiphon the shield is a hardened, horny structure, in Lithacrosiphon it is a calcareous cone, at the posterior end, a hardened caudal shield is sometimes present in Aspidosiphon. The digestive tract of sipunculans starts with the esophagus, located between the introvert retractor muscles, in the trunk the intestine runs posteriorly, forms a loop and turns anteriorly again. The downward and upward sections of the gut are coiled around each other, at the anterior end of the gut coil the rectum emerges and ends in the anus
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Bryozoa
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Bryozoa, are a phylum of aquatic invertebrate animals. Typically about 0.5 millimetres long, they are filter feeders that sieve food particles out of the using a retractable lophophore. Most marine species live in tropical waters, but a few occur in oceanic trenches, one class lives only in a variety of freshwater environments, and a few members of a mostly marine class prefer brackish water. Over 4,000 living species are known, one genus is solitary and the rest are colonial. The phylum was originally called Polyzoa, but this term was superseded by Bryozoa in 1831, another group of animals discovered subsequently, whose filtering mechanism looked similar, was also included in Bryozoa until 1869, when the two groups were noted to be very different internally. The more recently discovered group was given the name Entoprocta, while the original Bryozoa were called Ectoprocta, however, Bryozoa has remained the more widely used term for the latter group. Individuals in bryozoan colonies are called zooids, since they are not fully independent animals, all colonies contain autozooids, which are responsible for feeding and excretion. Colonies of some classes have various types of non-feeding specialist zooids, some of which are hatcheries for fertilized eggs, the class Cheilostomata have the largest number of species, possibly because they have the widest range of specialist zooids. A few species can creep very slowly by using spiny defensive zooids as legs, autozooids supply nutrients to non-feeding zooids by channels that vary between classes. Zooids have no special excretory organs, and the polypides of autozooids are scrapped when the polypides become overloaded by waste products, in autozooids the gut is U-shaped, with the mouth inside the crown of tentacles and the anus outside it. Colonies take a variety of forms, including fans, bushes, the Cheilostomata produce mineralized exoskeletons and form single-layered sheets which encrust over surfaces. Zooids of all the species are simultaneous hermaphrodites. Although those of marine species function first as males and then as females. All species emit sperm into the water, some also release ova into the water, while others capture sperm via their tentacles to fertilize their ova internally. In some species the larvae have large yolks, go to feed, others produce larvae that have little yolk but swim and feed for a few days before settling. After settling, all larvae undergo a metamorphosis that destroys. Freshwater species also produce statoblasts that lie dormant until conditions are favorable, predators of marine bryozoans include nudibranchs, fish, sea urchins, pycnogonids, crustaceans, mites and starfish. Freshwater bryozoans are preyed on by snails, insects, and fish, in Thailand, many populations of one freshwater species have been wiped out by an introduced species of snail
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Nematomorpha
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Nematomorpha are a phylum of parasitoid animals superficially similar to nematode worms in morphology, hence the name. They range in size in most species from 50 to 100 millimetres long and can reach in extreme cases up to 2 metres, Horsehair worms can be discovered in damp areas such as watering troughs, swimming pools, streams, puddles, and cisterns. The adult worms are free-living, but the larvae are parasitic on arthropods, such as beetles, cockroaches, mantids, orthopterans, about 351 freshwater species are known and a conservative estimate suggests that there may be about 2000 freshwater species worldwide. The name Gordian stems from the legendary Gordian knot and this relates to the fact that nematomorpha often tie themselves in knots. Nematomorphs possess an external cuticle without cilia, internally, they have only longitudinal muscle and a non-functional gut, with no excretory, respiratory or circulatory systems. The nervous system consists of a ring near the anterior end of the animal. Reproductively, they are dioecious, with the fertilization of eggs that are then laid in gelatinous strings. Adults have cylindrical gonads, opening into the cloaca, the larvae have rings of cuticular hooks and terminal stylets that are believed to be used to enter the hosts. Once inside the host, the larvae live inside the haemocoel, development into the adult form takes weeks or months, and the larva moults several times as it grows in size. The adults are mostly free-living in freshwater or marine environments, P. tricuspidatus is also remarkably able to survive the predation of their host, being able to wiggle out of the predator that has eaten the host. Nematomorphs can be confused with nematodes, particularly mermithid worms, unlike nematomorphs, mermithids do not have a terminal cloaca. Male mermithids have one or two spicules just before the end apart from having a thinner, smoother cuticle, without areoles, the phylum is placed along with the Ecdysozoa clade of moulting organisms that include the Arthropoda. Their closest relatives are the nematodes, the two phyla make up the group Nematoida in the clade Cycloneuralia. During the larval stage, the show a resemblance to adult kinorhyncha and some species of Loricifera and Priapulida. Relationships within the phylum are still unclear, but two classes are recognised. The five marine species of nematomorph are contained in Nectonematoida, adults are planktonic and the larvae parasitise decapod crustaceans, especially crabs. They are characterized by a row of natotory setae along each side of the body, dorsal and ventral longitudinal epidermal cords. The approximately 320 remaining species are distributed into two families and seven genera within order Gordioida, gordioidean adults are free-living in freshwater or semiterrestrial habitats and larvae parasitise insects, primarily orthopterans
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Phoronid
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Phoronids are a small phylum of marine animals that filter-feed with a lophophore, and build upright tubes of chitin to support and protect their soft bodies. They live in most of the oceans and seas including the Arctic Ocean but excluding the Antarctic Ocean, most adult phoronids are 2 cm long and about 1.5 mm wide, although the largest are 50 cm long. The bottom end of the body is an ampulla, which anchors the animal in the tube and enables it to retract its body very quickly when threatened. When the lophophore is extended at the top of the body, cilia on the sides of the tentacles draw food particles to the mouth, unwanted material can be excluded by closing a lid above the mouth or be rejected by the tentacles, whose cilia can switch into reverse. The food then moves down to the stomach, which is in the ampulla, solid wastes are moved up the intestine and out through the anus, which is outside and slightly below the lophophore. A blood vessel leads up the middle of the body from the stomach to a vessel at the base of the lophophore. A pair of blood vessels near the wall lead downward from the lophophore ring to the stomach. There is no heart, but the vessels can contract in waves to move the blood. Phoronids do not ventilate their trunks with oxygenated water, but rely on respiration through the lophophore, the blood contains hemoglobin, which is unusual in such small animals and seems to be an adaptation to anoxic and hypoxic environments. The blood of Phoronis architecta carries twice as much oxygen as a human of the same weight, two metanephridia filter the body fluid, returning any useful products and dumping the remaining soluble wastes through a pair of pores beside the anus. One species builds colonies by budding or by splitting into top and bottom sections, the eggs of most species form free-swimming actinotroch larvae, which feed on plankton. One species forms a slug-like larva, and the larvae of a few species are not known, Phoronids live for about one year. Some species live separately, in tubes embedded in soft sediment, while others form tangled masses buried in or encrusting rocks. In some habitats populations of phoronids reach tens of thousand of individuals per square meter, the actinotroch larvae are familiar among plankton, and sometimes account for a significant proportion of the zooplankton biomass. Predators include fish, gastropods, and nematodes, one phoronid species is unpalatable to many epibenthic predators. Various parasites infest phoronids body cavities, digestive tract and tentacles and it is unknown whether phoronids have any significance for humans. The International Union for Conservation of Nature has not listed any phoronid species as endangered, as of 2010 there are no indisputable body fossils of phoronids. There is good evidence that phoronids created trace fossils found in the Silurian, Devonian, Permian, Jurassic and Cretaceous periods, Phoronids, brachiopods and bryozoans have collectively been called lophophorates, because all use lophophores to feed
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Nemertea
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Nemertea is a phylum of invertebrate animals also known as, Splooge Worms, ribbon worms or proboscis worms. Alternative names for the phylum have included Nemertini, Nemertinea and Rhynchocoela, although most are less than 20 centimetres long, one specimen has been estimated at 54 metres. Most are very slim, usually only a few wide, although a few have relatively short. Many have patterns of yellow, orange, red and green coloration, the foregut, stomach and intestine run a little below the midline of the body, the anus is at the tip of the tail, and the mouth is under the front. A little above the gut is the rhynchocoel, a cavity which runs above the midline. All species have a proboscis which lies in the rhynchocoel when inactive but everts to emerge just above the mouth, a very stretchy muscle in the back of the rhynchocoel pulls the proboscis in when an attack ends. A few species with stubby bodies filter feed and have suckers at the front and back ends, the brain is a ring of four ganglia, positioned around the rhynchocoel near its front end. At least a pair of nerve cords connect to the brain. Most nemerteans have various chemoreceptors, and on their heads some species have a number of pigment-cup ocelli and these ocelli can detect light but can not form an image. They have at least two lateral vessels which are joined at the ends to form a loop, and these, there is no heart, and the flow of fluid depends on contraction of muscles in the vessels and the body wall. To filter out soluble waste products, flame cells are embedded in the front part of the two lateral fluid vessels, and remove the wastes through a network of pipes to the outside. All nemerteans move slowly, using their external cilia to glide on surfaces on a trail of slime, while larger species use muscular waves to crawl, a few live in the open ocean while the rest find or make hiding places on the bottom. About a dozen species inhabit freshwater, mainly in the tropics and subtropics, most nemerteans are carnivores, feeding on annelids, clams and crustaceans. A few species are scavengers, and a few species live commensally inside the cavity of molluscs. Some species have devastated commercial fishing of clams and crabs, two species are sold as fish bait. In most species the sexes are separate, but all the species are hermaphroditic. Nemerteans often have numerous temporary gonads, and build temporary gonoducts, one per gonad, the eggs are generally fertilised externally. Some species shed them into the water, and others protect their eggs in various ways, the fertilized egg divides by spiral cleavage and grows by determinate development, in which the fate of a cell can usually be predicted from its predecessors in the process of division
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