Arthropods are covered with a tough, resilient integument or exoskeleton of chitin. The exoskeleton will have thickened areas in which the chitin is reinforced or stiffened by materials such as minerals or hardened proteins; this happens in parts of the body where there is a need for elasticity. The mineral crystals calcium carbonate, are deposited among the chitin and protein molecules in a process called biomineralization; the crystals and fibres interpenetrate and reinforce each other, the minerals supplying the hardness and resistance to compression, while the chitin supplies the tensile strength. Biomineralization occurs in crustaceans. In either case, in contrast to the carapace of a tortoise or the cranium of a vertebrate, the exoskeleton has little ability to grow or change its form once it has matured. Except in special cases, whenever the animal needs to grow, it moults, shedding the old skin after growing a new skin from beneath. A typical arthropod exoskeleton is a multi-layered structure with four functional regions: epicuticle, procuticle and basement membrane.
Of these, the epicuticle is a multi-layered external barrier that in terrestrial arthropods, acts as a barrier against desiccation. The strength of the exoskeleton is provided by the underlying procuticle, in turn secreted by the epidermis. Arthropod cuticle is a biological composite material, consisting of two main portions: fibrous chains of alpha-chitin within a matrix of silk-like and globular proteins, of which the best-known is the rubbery protein called resilin; the relative abundance of these two main components varies from 50/50 to 80/20 chitin protein, with softer parts of the exoskeleton having a higher proportion of chitin. The cuticle is soft when first secreted, but it soon hardens as required, in a process of sclerotization; the process is poorly understood, but it involves forms of tanning in which phenolic chemicals crosslink protein molecules or anchor them to surrounding molecules such as chitins. Part of the effect is to make the tanned material hydrophobic. By varying the types of interaction between the proteins and chitins, the insect metabolism produces regions of exoskeleton that differ in their wet and dry behaviour, their colour and their mechanical properties.
In addition to the chitino-proteinaceous composite of the cuticle, many crustaceans, some myriapods and the extinct trilobites further impregnate the cuticle with mineral salts, above all calcium carbonate, which can make up to 40% of the cuticle. The armoured product has great mechanical strength; the two layers of the cuticle have different properties. The outer layer is where most of the thickening, biomineralization and sclerotisation takes place, its material tends to be strong under compressive stresses, though weaker under tension; when a rigid region fails under stress, it does so by cracking. The inner layer is not as sclerotised, is correspondingly softer but tougher; this combination is effective in resisting predation, as predators tend to exert compression on the outer layer, tension on the inner. Its degree of sclerotisation or mineralisation determines. Below a certain degree of deformation changes of shape or dimension of the cuticle are elastic and the original shape returns after the stress is removed.
Beyond that level of deformation, non-reversible, plastic deformation occurs until the cuticle cracks or splits. The less sclerotised the cuticle, the greater the deformation required to damage the cuticle irreversibly. On the other hand, the more the cuticle is armoured, the greater the stress required to deform it harmfully; as a rule, the arthropod exoskeleton is divided into different functional units, each comprising a series of grouped segments. Such a group is called a tagma, the tagmata are adapted to different functions in a given arthropod body. For example, tagmata of insects include the head, a fused capsule, the thorax as nearly a fixed capsule, the abdomen divided into a series of articulating segments; each segment has sclerites according to its requirements for external rigidity. In some beetles most of the joints are so connected, that the body is in an armoured, rigid box. However, in most Arthropoda the bodily tagmata are so connected and jointed with flexible cuticle and muscles that they have at least some freedom of movement, many such animals, such as the Chilopoda or the larvae of mosquitoes are mobile indeed.
In addition, the limbs of arthropods are jointed, so characteristically that the name "Arthropoda" means "jointed legs" in reflection of the fact. The internal surface of the exoskeleton is infolded, forming a set of structures called apodemes that serve for the attachment of muscles, functionally amounting to endoskeletal components, they are complex in some groups in Crustacea. The chemical and physical nature of the arthropod exoskeleton limits its ability to stretch or change shape as the animal grows. In some special cases, such as the abdomens of termite queens and honeypot ants means that continuous growth of arthropods is not possible. Therefore, growth is periodic and concentrated into a period of time w
A xerophyte is a species of plant that has adaptations to survive in an environment with little liquid water, such as a desert or an ice- or snow-covered region in the Alps or the Arctic. Popular examples of xerophytes are cacti and some Gymnosperm plants; the structural features and fundamental chemical processes of xerophytes are variously adapted to conserve water common to store large quantities of water, during dry periods. Other species are able to survive long periods of extreme dryness or desiccation of their tissues, during which their metabolic activity may shut down. Plants with such morphological and physiological adaptations are xeromorphic. Xerophytes such as cacti are capable of withstanding extended periods of dry conditions as they have deep-spreading roots and capacity to store water; the leaves are thorny that prevents loss of water and moisture. Their fleshy stems can store water. Plants absorb water from the soil, which evaporates from their shoots and leaves. In dry environments, a typical mesophytic plant would evaporate water faster than the rate of water uptake from the soil, leading to wilting and death.
Xerophytic plants exhibit a diversity of specialized adaptations to survive in such water-limiting conditions. They may use water from their own storage, allocate water to sites of new tissue growth, or lose less water to the atmosphere and so channel a greater proportion of water from the soil to photosynthesis and growth. Different plant species possess different qualities and mechanisms to manage water supply, enabling them to survive. Cacti and other succulents are found in deserts, where there is little rainfall. Other xerophytes, such as certain bromeliads, can survive through both wet and dry periods and can be found in seasonally-moist habitats such as tropical forests, exploiting niches where water supplies are too intermittent for mesophytic plants to survive. Chaparral plants are adapted to Mediterranean climates, which have wet winters and dry summers. Plants that live under arctic conditions have a need for xerophytic adaptations, since water is unavailable for uptake when the ground is frozen, such as the European resurrection plants Haberlea rhodopensis and Ramonda serbica.
In an environment with high salinity such as mangrove swamps and semi-deserts, water uptake by plants is a challenge due to the high salt ion levels. Besides that, such environments may cause an excess of ions to accumulate in the cells, damaging. Halophytes and xerophytes evolved to survive in such environments; some xerophytes may be considered halophytes, halophytes are not xerophytes. The succulent xerophyte Zygophyllum xanthoxylum, for example, have specialised protein transporters in their cells which allow storage of excess ions in their vacuole to maintain normal cytosolic pH and ionic composition. There are many factors which affect water availability, the major limiting factor of seed germination, seedling survival, plant growth; these factors include infrequent raining, intense sunlight and warm weather leading to faster water evaporation. An extreme environmental pH and high salt content of water disrupt plants' water uptake. Succulent plants leaves; these include plants from the Cactaceae family, which have round can store a lot of water.
The leaves are vestigial, as in the case of cacti, wherein the leaves are reduced to spines, or they do not have leaves at all. These include the C4 perennial woody plant, Haloxylon ammodendron, a native of northwest China. Non-succulent perennials endure long and continuous shortage of water in the soil; these euxerophytes. Water deficiency reaches 60–70% of their fresh weight, as a result of which the growth process of the whole plant is hindered during cell elongation; the plants which survive drought are, understandably and weak. Ephemerals are the'drought escaping' kind, not true xerophytes, they do not endure drought, only escape it. With the onset of rainfall, the plant seeds germinate grow to maturity and set seed, i.e. the entire life cycle is completed before the soil dries out again. Most of these plants are small, dense shrubs represented by species of Papilionaceae, some inconspicuous Compositae, a few Zygophyllaceae and some grasses. Water is stored at below ground level, they may be dormant during drought conditions and are, known as drought evaders.
Shrubs which grow in arid and semi-arid regions are xeromorphic. For example, Caragana korshinskii, Artemisia sphaerocephala, Hedysarum scoparium are shrubs potent in the semi-arid regions of the northwest China desert; these psammophile shrubs are not only edible to grazing animals in the area, they play a vital role in the stabilisation of desert sand dunes. Bushes called semi-shrubs occur in sandy desert region in deep sandy soils at the edges of the dunes. One example is a perennial resurrection semi-shrub. Compared to other dominant arid xerophytes, an adult R. soongorica, bush has a strong resistance to water scarcity, hence, it is considered a super-xerophytes. If the water potential inside a leaf is higher than outside, the water vapour will diffuse out of the leaf down this gradient; this loss of water vapour from the leaves is called transpiration, the water vapour diffuses through the open stomata. Transpiration is inevitable for plants.
Invertebrates are animals that neither possess nor develop a vertebral column, derived from the notochord. This includes all animals apart from the subphylum Vertebrata. Familiar examples of invertebrates include arthropods, mollusks and cnidarians; the majority of animal species are invertebrates. Many invertebrate taxa have a greater number and variety of species than the entire subphylum of Vertebrata; some of the so-called invertebrates, such as the Tunicata and Cephalochordata are more related to the vertebrates than to other invertebrates. This makes the invertebrates paraphyletic, so the term has little meaning in taxonomy; the word "invertebrate" comes from the Latin word vertebra, which means a joint in general, sometimes a joint from the spinal column of a vertebrate. The jointed aspect of vertebra is derived from the concept of turning, expressed in the root verto or vorto, to turn; the prefix in- means "not" or "without". The term invertebrates is not always precise among non-biologists since it does not describe a taxon in the same way that Arthropoda, Vertebrata or Manidae do.
Each of these terms describes a valid taxon, subphylum or family. "Invertebrata" is a term of convenience, not a taxon. The Vertebrata as a subphylum comprises such a small proportion of the Metazoa that to speak of the kingdom Animalia in terms of "Vertebrata" and "Invertebrata" has limited practicality. In the more formal taxonomy of Animalia other attributes that logically should precede the presence or absence of the vertebral column in constructing a cladogram, for example, the presence of a notochord; that would at least circumscribe the Chordata. However the notochord would be a less fundamental criterion than aspects of embryological development and symmetry or bauplan. Despite this, the concept of invertebrates as a taxon of animals has persisted for over a century among the laity, within the zoological community and in its literature it remains in use as a term of convenience for animals that are not members of the Vertebrata; the following text reflects earlier scientific understanding of the term and of those animals which have constituted it.
According to this understanding, invertebrates do not possess a skeleton of bone, either internal or external. They include hugely varied body plans. Many have like jellyfish or worms. Others have outer shells like those of insects and crustaceans; the most familiar invertebrates include the Protozoa, Coelenterata, Nematoda, Echinodermata and Arthropoda. Arthropoda include insects and arachnids. By far the largest number of described invertebrate species are insects; the following table lists the number of described extant species for major invertebrate groups as estimated in the IUCN Red List of Threatened Species, 2014.3. The IUCN estimates that 66,178 extant vertebrate species have been described, which means that over 95% of the described animal species in the world are invertebrates; the trait, common to all invertebrates is the absence of a vertebral column: this creates a distinction between invertebrates and vertebrates. The distinction is one of convenience only. Being animals, invertebrates are heterotrophs, require sustenance in the form of the consumption of other organisms.
With a few exceptions, such as the Porifera, invertebrates have bodies composed of differentiated tissues. There is typically a digestive chamber with one or two openings to the exterior; the body plans of most multicellular organisms exhibit some form of symmetry, whether radial, bilateral, or spherical. A minority, exhibit no symmetry. One example of asymmetric invertebrates includes all gastropod species; this is seen in snails and sea snails, which have helical shells. Slugs appear externally symmetrical. Other gastropods develop external asymmetry, such as Glaucus atlanticus that develops asymmetrical cerata as they mature; the origin of gastropod asymmetry is a subject of scientific debate. Other examples of asymmetry are found in hermit crabs, they have one claw much larger than the other. If a male fiddler loses its large claw, it will grow another on the opposite side after moulting. Sessile animals such as sponges are asymmetrical alongside coral colonies. Neurons differ in invertebrates from mammalian cells.
Invertebrates cells fire in response to similar stimuli as mammals, such as tissue trauma, high temperature, or changes in pH. The first invertebrate in which a neuron cell was identified was the medicinal leech, Hirudo medicinalis. Learning and memory using nociceptors in the sea hare, Aplysia has been described. Mollusk neurons are able to detect tissue trauma. Neurons have been identified in a wide range of invertebrate species, including annelids, molluscs and arthropods. One type of invertebrate respi
The hymenium is the tissue layer on the hymenophore of a fungal fruiting body where the cells develop into basidia or asci, which produce spores. In some species all of the cells of the hymenium develop into basidia or asci, while in others some cells develop into sterile cells called cystidia or paraphyses. Cystidia are important for microscopic identification; the subhymenium consists of the supportive hyphae from which the cells of the hymenium grow, beneath, the hymenophoral trama, the hyphae that make up the mass of the hymenophore. The position of the hymenium is traditionally the first characteristic used in the classification and identification of mushrooms. Below are some examples of the diverse types which exist among the macroscopic Basidiomycota and Ascomycota. In agarics, the hymenium is on the vertical faces of the gills. In boletes, it is in a spongy mass of downward-pointing tubes. In puffballs, it is internal. In stinkhorns, it develops internally and is exposed in the form of a foul-smelling gel.
In cup fungi, it is on the concave surface of the cup. In teeth fungi, it grows on the outside of tooth-like spines. Régis Courtecuisse, Bernard Duhem: Guide des champignons de France et d'Europe. ISBN 2-603-00953-2 IMA Mycological Glossary: Hymenium IMA Mycological Glossary: Subhymenium APSnet Illustrated Glossary of Plant Pathology: Hymenium Hymenium of an ascomycete, Monilinia fructicola Jack Murphy Mycological Images: Hymenium Hymenium of a basidiomycete, Russula laurocerasi
Zoology is the branch of biology that studies the animal kingdom, including the structure, evolution, classification and distribution of all animals, both living and extinct, how they interact with their ecosystems. The term is derived from Ancient Greek ζῷον, zōion, i.e. "animal" and λόγος, logos, i.e. "knowledge, study". The history of zoology traces the study of the animal kingdom from ancient to modern times. Although the concept of zoology as a single coherent field arose much the zoological sciences emerged from natural history reaching back to the biological works of Aristotle and Galen in the ancient Greco-Roman world; this ancient work was further developed in the Middle Ages by Muslim physicians and scholars such as Albertus Magnus. During the Renaissance and early modern period, zoological thought was revolutionized in Europe by a renewed interest in empiricism and the discovery of many novel organisms. Prominent in this movement were Vesalius and William Harvey, who used experimentation and careful observation in physiology, naturalists such as Carl Linnaeus, Jean-Baptiste Lamarck, Buffon who began to classify the diversity of life and the fossil record, as well as the development and behavior of organisms.
Microscopy revealed the unknown world of microorganisms, laying the groundwork for cell theory. The growing importance of natural theology a response to the rise of mechanical philosophy, encouraged the growth of natural history. Over the 18th, 19th, 20th centuries, zoology became an professional scientific discipline. Explorer-naturalists such as Alexander von Humboldt investigated the interaction between organisms and their environment, the ways this relationship depends on geography, laying the foundations for biogeography and ethology. Naturalists began to reject essentialism and consider the importance of extinction and the mutability of species. Cell theory provided a new perspective on the fundamental basis of life; these developments, as well as the results from embryology and paleontology, were synthesized in Charles Darwin's theory of evolution by natural selection. In 1859, Darwin placed the theory of organic evolution on a new footing, by his discovery of a process by which organic evolution can occur, provided observational evidence that it had done so.
Darwin gave a new direction to morphology and physiology, by uniting them in a common biological theory: the theory of organic evolution. The result was a reconstruction of the classification of animals upon a genealogical basis, fresh investigation of the development of animals, early attempts to determine their genetic relationships; the end of the 19th century saw the fall of spontaneous generation and the rise of the germ theory of disease, though the mechanism of inheritance remained a mystery. In the early 20th century, the rediscovery of Mendel's work led to the rapid development of genetics, by the 1930s the combination of population genetics and natural selection in the modern synthesis created evolutionary biology. Cell biology studies the structural and physiological properties of cells, including their behavior and environment; this is done on both the microscopic and molecular levels, for single-celled organisms such as bacteria as well as the specialized cells in multicellular organisms such as humans.
Understanding the structure and function of cells is fundamental to all of the biological sciences. The similarities and differences between cell types are relevant to molecular biology. Anatomy considers the forms of macroscopic structures such as organs and organ systems, it focuses on how organs and organ systems work together in the bodies of humans and animals, in addition to how they work independently. Anatomy and cell biology are two studies that are related, can be categorized under "structural" studies. Physiology studies the mechanical and biochemical processes of living organisms by attempting to understand how all of the structures function as a whole; the theme of "structure to function" is central to biology. Physiological studies have traditionally been divided into plant physiology and animal physiology, but some principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can apply to human cells.
The field of animal physiology extends the tools and methods of human physiology to non-human species. Physiology studies how for example nervous, endocrine and circulatory systems and interact. Evolutionary research is concerned with the origin and descent of species, as well as their change over time, includes scientists from many taxonomically oriented disciplines. For example, it involves scientists who have special training in particular organisms such as mammalogy, herpetology, or entomology, but use those organisms as systems to answer general questions about evolution. Evolutionary biology is based on paleontology, which uses the fossil record to answer questions about the mode and tempo of evolution, on the developments in areas such as population genetics and evolutionary theory. Following the development of DNA fingerprinting techniques in the late 20th century, the application of these techniques in zoology has increased the understanding of animal populations. In the 1980s, developmental biology re-entered evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology.
Related fields considered part of evolutionary biology are phylogenetics and taxonomy. Scientific classification in zoology, is a method by which
A mushroom, or toadstool, is the fleshy, spore-bearing fruiting body of a fungus produced above ground on soil or on its food source. The standard for the name "mushroom" is Agaricus bisporus. "Mushroom" describes a variety of other gilled fungi, with or without stems, therefore the term is used to describe the fleshy fruiting bodies of some Ascomycota. These gills produce microscopic spores that help the fungus spread across the ground or its occupant surface. Forms deviating from the standard morphology have more specific names, such as "bolete", "puffball", "stinkhorn", "morel", gilled mushrooms themselves are called "agarics" in reference to their similarity to Agaricus or their order Agaricales. By extension, the term "mushroom" can refer to either the entire fungus when in culture, the thallus of species forming the fruiting bodies called mushrooms, or the species itself. Identifying mushrooms requires a basic understanding of their macroscopic structure. Most are gilled, their spores, called basidiospores, are produced on the gills and fall in a fine rain of powder from under the caps as a result.
At the microscopic level, the basidiospores are shot off basidia and fall between the gills in the dead air space. As a result, for most mushrooms, if the cap is cut off and placed gill-side-down overnight, a powdery impression reflecting the shape of the gills is formed; the color of the powdery print, called a spore print, is used to help classify mushrooms and can help to identify them. Spore print colors include white, black, purple-brown, pink and creamy, but never blue, green, or red. While modern identification of mushrooms is becoming molecular, the standard methods for identification are still used by most and have developed into a fine art harking back to medieval times and the Victorian era, combined with microscopic examination; the presence of juices upon breaking, bruising reactions, tastes, shades of color, habitat and season are all considered by both amateur and professional mycologists. Tasting and smelling mushrooms carries its own hazards because of poisons and allergens.
Chemical tests are used for some genera. In general, identification to genus can be accomplished in the field using a local mushroom guide. Identification to species, requires more effort. However, over-mature specimens cease producing spores. Many novices have mistaken humid water marks on paper for white spore prints, or discolored paper from oozing liquids on lamella edges for colored spored prints. Typical mushrooms are the fruit bodies of members of the order Agaricales, whose type genus is Agaricus and type species is the field mushroom, Agaricus campestris. However, in modern molecularly defined classifications, not all members of the order Agaricales produce mushroom fruit bodies, many other gilled fungi, collectively called mushrooms, occur in other orders of the class Agaricomycetes. For example, chanterelles are in the Cantharellales, false chanterelles such as Gomphus are in the Gomphales, milk-cap mushrooms and russulas, as well as Lentinellus, are in the Russulales, while the tough, leathery genera Lentinus and Panus are among the Polyporales, but Neolentinus is in the Gloeophyllales, the little pin-mushroom genus, along with similar genera, are in the Hymenochaetales.
Within the main body of mushrooms, in the Agaricales, are common fungi like the common fairy-ring mushroom, enoki, oyster mushrooms, fly agarics and other Amanitas, magic mushrooms like species of Psilocybe, paddy straw mushrooms, shaggy manes, etc. An atypical mushroom is the lobster mushroom, a deformed, cooked-lobster-colored parasitized fruitbody of a Russula or Lactarius and deformed by the mycoparasitic Ascomycete Hypomyces lactifluorum. Other mushrooms are not gilled, so the term "mushroom" is loosely used, giving a full account of their classifications is difficult; some have pores underneath, others have spines, such as the hedgehog mushroom and other tooth fungi, so on. "Mushroom" has been used for polypores, jelly fungi, coral fungi, bracket fungi and cup fungi. Thus, the term is more one of common application to macroscopic fungal fruiting bodies than one having precise taxonomic meaning. 14,000 species of mushrooms are described. The terms "mushroom" and "toadstool" go back centuries and were never defined, nor was there consensus on application.
Between 1400 and 1600 AD, the terms mushrom, muscheron, mussheron, or musserouns were used. The term "mushroom" and its variations may have been derived from the French word mousseron in reference to moss. Delineation between edible and poisonous fungi is not clear-cut, so a "mushroom" may be edible, poisonous, or unpalatable. Cultural or social phobias of mushrooms and fungi may be related; the term "fungophobia" was coined by William Delisle Hay of England, who noted a national superstition or fear of "toadstools". The word "toadstool" has apparent analogies in German Krötenschwamm. In German folklore and old fair
The nematodes or roundworms constitute the phylum Nematoda. They are a diverse animal phylum inhabiting a broad range of environments. Taxonomically, they are classified along with insects and other moulting animals in the clade Ecdysozoa, unlike flatworms, have tubular digestive systems with openings at both ends. Nematode species can be difficult to distinguish from one another. Estimates of the number of nematode species described to date vary by author and may change over time. A 2013 survey of animal biodiversity published in the mega journal Zootaxa puts this figure at over 25,000. Estimates of the total number of extant species are subject to greater variation. A referenced article published in 1993 estimated there may be over 1 million species of nematode, a claim which has since been repeated in numerous publications, without additional investigation, in an attempt to accentuate the importance and ubiquity of nematodes in the global ecosystem. Many other publications have since vigorously refuted this claim on the grounds that it is unsupported by fact, is the result of speculation and sensationalism.
More recent, fact-based estimates have placed the true figure closer to 40,000 species worldwide. Nematodes have adapted to nearly every ecosystem: from marine to fresh water, from the polar regions to the tropics, as well as the highest to the lowest of elevations, they are ubiquitous in freshwater and terrestrial environments, where they outnumber other animals in both individual and species counts, are found in locations as diverse as mountains and oceanic trenches. They are found in every part of the earth's lithosphere at great depths, 0.9–3.6 km below the surface of the Earth in gold mines in South Africa. They represent 90% of all animals on the ocean floor, their numerical dominance exceeding a million individuals per square meter and accounting for about 80% of all individual animals on earth, their diversity of lifecycles, their presence at various trophic levels point to an important role in many ecosystems. They have been shown to play crucial roles in polar ecosystem; the 2,271 genera are placed in 256 families.
The many parasitic forms include pathogens in animals. A third of the genera occur as parasites of vertebrates. Nathan Cobb, a nematologist, described the ubiquity of nematodes on Earth as thus:In short, if all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, if, as disembodied spirits, we could investigate it, we should find its mountains, vales, rivers and oceans represented by a film of nematodes; 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 highways; the location of the various plants and animals would still be decipherable, had we sufficient knowledge, in many cases their species could be determined by an examination of their erstwhile nematode parasites. Modern Latin compound of nemat- "thread" + -odes "like, of the nature of". In 1758, Linnaeus described some nematode genera included in the Vermes.
The name of the group Nematoda, informally called "nematodes", came from Nematoidea 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 and Cestoidea, it formed the obsolete group Entozoa, created by Rudolphi, they were 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; the first clear distinction between the nemas and gordiids was realized by Vejdovsky when he named a group to contain the horsehair worms the order Nematomorpha. In 1919, Nathan Cobb proposed, he argued they should be called "nema" in English rather than "nematodes" and defined the taxon Nemates, listing Nematoidea sensu restricto as a synonym.
However, in 1910, Grobben proposed the phylum Aschelminthes and the nematodes were included in as class Nematoda along with class Rotifera, class Gastrotricha, class Kinorhyncha, class Priapulida, class Nematomorpha. In 1932, Potts elevated the class Nematoda to the level of phylum. Despite Potts' classification being equivalent to Cobbs', both names have been used and Nematode became a popular term in zoological science. Since Cobb was the first to include nematodes in a particular phylum separated from Nematomorpha, some researchers consider the valid taxon name to be Nemates or Nemata, rather than Nematoda, because of the zoological rule that gives priority to the first used term in case of synonyms; the phylogenetic relationships of the nematodes and their close relatives among the protostomian Metazoa are unresolved. Traditionally, they were held to b