The gastrotrichs (

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclatu ...

Gastrotricha), commonly referred to as hairybellies or hairybacks, are a group of microscopic (0.06-3.0 mm), worm-like, acoelomate

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

s, and are widely distributed and abundant in

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does in ...

and marine environments. They are mostly

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

and live within the periphyton, the layer of tiny organisms and detritus that is found on the seabed and the beds of other water bodies. The majority live on and between particles of

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

or on other submerged surfaces, but a few species are terrestrial and live on land in the film of water surrounding grains of

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...

. Gastrotrichs are divided into two

orders Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...

, the Macrodasyida which are marine (except for two species), and the Chaetonotida, some of which are marine and some freshwater. Nearly 800 species of gastrotrich have been described. Gastrotrichs have a simple body plan with a head region, with a brain and sensory organs, and a trunk with a simple gut and the reproductive organs. They have adhesive glands with which they can anchor themselves to the

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (locomotion), the surface over which an organism lo ...

and cilia with which they move around. They feed on detritus, sucking up organic particles with their muscular

pharynx The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its ...

. They are

hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have ...

s, the marine species producing eggs which develop directly into miniature adults. The freshwater species are parthenogenetic, producing unfertilised eggs, and at least one species is viviparous. Gastrotrichs mature with great rapidity and have lifespans of only a few days.

Etymology and taxonomy

The name "gastrotrich" comes from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

γαστήρ ''gaster'', meaning "stomach", and θρίξ ''thrix'', meaning "hair". The name was coined by the Russian zoologist Élie Metchnikoff in 1865. The common name "hairyback" apparently arises from a mistranslation of "gastrotrich". The relationship of gastrotrichs to other phyla is unclear. Morphology suggests that they are close to the Gnathostomulida, the Rotifera, or the Nematoda. On the other hand, genetic studies place them as close relatives of the

Platyhelminthes The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegment ...

, the

Ecdysozoa Ecdysozoa () is a group of protostome animals, including Arthropoda (insects, chelicerata, crustaceans, and myriapods), Nematoda, and several smaller phyla. They were first defined by Aguinaldo ''et al.'' in 1997, based mainly on phylogeneti ...

or the

Lophotrochozoa Lophotrochozoa (, "crest/wheel animals") is a clade of protostome animals within the Spiralia. The taxon was established as a monophyletic group based on molecular evidence. The clade includes animals like annelids, molluscs, bryozoans, bra ...

. As of 2011, around 790 species have been described. The phylum contains a single class, divided into two orders: the Macrodasyida and the Chaetonotida. Edward Ruppert ''et al.'' report that the Macrodasyida are wholly marine, but two rare and poorly known species, ''Marinellina flagellata'' and ''Redudasys fornerise'', are known from fresh water. The Chaetonotida comprises both marine and freshwater species.

Anatomy

Gastrotrichs vary in size from about in body length. They are bilaterally symmetrical, with a transparent strap-shaped or bowling pin-shaped body, arched dorsally and flattened ventrally. The anterior end is not clearly defined as a head but contains the sense organs, brain and pharynx. Cilia are found around the mouth and on the ventral surface of the head and body. The trunk contains the gut and the reproductive organs. At the posterior end of the body are two projections with cement glands that serve in adhesion. This is a double-gland system where one gland secretes the glue and another secretes a de-adhesive agent to sever the connection. In the Macrodasyida, there are additional adhesive glands at the anterior end and on the sides of the body. Diplodasys rothei legends

The body wall consists of a cuticle, an

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the ...

and longitudinal and circular bands of muscle fibres. In some

primitive Primitive may refer to: Mathematics * Primitive element (field theory) * Primitive element (finite field) * Primitive cell (crystallography) * Primitive notion, axiomatic systems * Primitive polynomial (disambiguation), one of two concepts * Pr ...

species, each epidermal cell has a single cilium, a feature shared only by the

gnathostomula Gnathostomulidae is a family of worms belonging to the order Bursovaginoidea Bursovaginoidea is one of the two orders in the phylum Gnathostomulida. Appearance and anatomy Bursovaginoids are rather small, ranging from a half of a millimeter ...

ns. The whole ventral surface of the animal may be ciliated or the cilia may be arranged in rows, patches or transverse bands. The cuticle is locally thickened in some gastrotrichs and forms scales, hooks and spines. There is no coelom (body cavity) and the interior of the animal is filled with poorly differentiated

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tissue ...

. In the macrodasyidans, Y-shaped cells, each containing a vacuole, surround the gut and may function as a hydrostatic skeleton. The mouth is at the anterior end and opens into an elongated muscular

with a triangular or Y-shaped lumen, lined by myoepithelial cells. The pharynx opens into a cylindrical intestine, which is lined with glandular and digestive cells. The anus is located on the ventral surface close to the posterior of the body. In some species, there are pores in the pharynx opening to the ventral surface; these contain valves and may allow

egestion Defecation (or defaecation) follows digestion, and is a necessary process by which organisms eliminate a solid, semisolid, or liquid waste material known as feces from the digestive tract via the anus. The act has a variety of names ranging f ...

of any excess water swallowed while feeding. In the chaetonotidans, the excretory system consists of a single pair of protonephridia, which open through separate pores on the lateral underside of the animal, usually in the midsection of the body. In the macrodasyidans, there are several pairs of these opening along the side of the body. Nitrogenous waste is probably excreted through the body wall, as part of respiration, and the protonephridia are believed to function mainly in osmoregulation. Unusually, the protonephridia do not take the form of flame cells, but, instead, the excretory cells consist of a skirt surrounding a series of

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

ic rods that in turn enclose a central flagellum. These cells, termed ''cyrtocytes'', connect to a single outlet cell which passes the excreted material into the protonephridial duct. As is typical for such small animals, there are no respiratory or circulatory organs. The nervous system is relatively simple. The brain consists of two ganglia, one on either side of the pharynx, connected by a commissure. From these lead a pair of nerve cords which run along either side of the body beside the longitudinal muscle bands. The primary sensory organs are the bristles and ciliated tufts of the body surface which function as mechanoreceptors. There are also ciliated pits on the head, simple ciliary photoreceptors and fleshy appendages which act as chemoreceptors.

Distribution and habitat

Gastrotrichs are cosmopolitan in distribution. They inhabit the interstitial spaces between particles in marine and freshwater environments, the surfaces of aquatic plants and other submerged objects and the surface film of water surrounding soil particles on land. They are also found in stagnant pools and anaerobic mud, where they thrive even in the presence of

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The und ...

. When pools dry up they can survive periods of desiccation as eggs, and some species are capable of forming cysts in harsh conditions. In marine sediments they have been known to reach 364 individuals per making them the third most common invertebrate in the sediment after nematodes and harpacticoid copepods. In freshwater they may reach a density of 158 individuals per and are the fifth most abundant group of invertebrates in the sediment.

Behaviour and ecology

In marine and freshwater environments, gastrotrichs form part of the benthic community. They are detritivores and are microphagous, sucking dead or living organic material, diatoms,

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

and small protozoa into their mouths by the muscular action of the pharynx. They are themselves eaten by

turbellaria The Turbellaria are one of the traditional sub-divisions of the phylum Platyhelminthes (flatworms), and include all the sub-groups that are not exclusively parasitic. There are about 4,500 species, which range from to large freshwater forms mor ...

ns and other small macrofauna. Like many microscopic animals, gastrotrich locomotion is primarily powered by hydrostatics, but movement occurs through different methods in different members of the group. Chaetonotids only have adhesive glands at the back and, in them, locomotion typically proceeds in a smooth gliding manner; the whole body is propelled forward by the rhythmic action of the cilia on the ventral surface. In the pelagic chaetonotid genus '' Stylochaeta'', however, movement proceeds in jerks as the long, muscle-activated spines are forced rhythmically towards the side of the body. By contrast, with chaetonotids, macrodasyidans typically have multiple adhesive glands and move forward with a creeping action similar to that of a "looper" caterpillar. In response to a threat, the head and trunk can be rapidly pulled backwards, or the creeping movement can be reversed. Muscular action is important when the animal turns sideways and during copulation, when two individuals twine around each other.

Reproduction and lifespan

Gastrotrich reproduction and reproductive behaviour has been little studied. That of macrodasiyds probably most represents that of the ancestral lineage and these more primitive gastrotrichs are simultaneous

s, possessing both male and female sex organs. There is generally a single pair of gonads, the anterior portion of which contains sperm-producing cells and the posterior portion producing ova. The sperm is sometimes packaged in spermatophores and is released through male gonopores that open, often temporarily, on the underside of the animal, roughly two-thirds of the way along the body. A copulatory organ on the tail collects the sperm and transfers it to the partner's seminal receptacle through the female gonopore. Details of the process and the behaviour involved vary with the species, and there is a range of different accessory reproductive organs. During copulation, the "male" individual uses his copulatory organ to transfer sperm to his partner's gonopore and fertilisation is internal. The fertilised eggs are released by rupture of the body wall which afterwards repairs itself. As is the case in most

protostome Protostomia () is the clade of animals once thought to be characterized by the formation of the organism's mouth before its anus during embryonic development. This nature has since been discovered to be extremely variable among Protostomia's mem ...

s, development of the embryo is

determinate In logic and philosophy (especially metaphysics), a property is a characteristic of an object; a red object is said to have the property of redness. The property may be considered a form of object in its own right, able to possess other propertie ...

, with each cell destined to become a specific part of the animal's body. At least one species of gastrotrich, '' Urodasys viviparus'', is viviparous. Many species of chaetotonid gastrotrichs reproduce entirely by

parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and developmen ...

. In these species, the male portions of the reproductive system are degenerate and non-functional, or, in many cases, entirely absent. Though the eggs have a diameter of less than 50

µm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

, they are still very large in comparison with the animals' size. Some species are capable of laying eggs that remain

dormant Dormant, "sleeping", may refer to: Science *Dormancy Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps ...

during times of desiccation or low temperatures; these species, however, are also able to produce regular eggs, which hatch in one to four days, when environmental conditions are more favourable. The eggs of all gastrotrichs undergo direct development and hatch into miniature versions of the adult. The young typically reach sexual maturity in about three days. In the laboratory, ''

Lepidodermella squamatum ''Lepidodermella squamata'' is a freshwater species of minute worm in the phylum Gastrotricha. Description ''Lepidodermella squamata'' is a small worm-like organism growing to a length of 190 μm (0.007 inch). It is roughly cylindrical with a he ...

'' has lived for up to forty days, producing four or five eggs during the first ten days of life. Gastrotrichs demonstrate eutely, each species having an invariant genetically fixed number of cells as adults. Cell division ceases at the end of embryonic development and further growth is solely due to cell enlargement.

Classification

Gastrotricha is divided into two orders and a number of families: Order Macrodasyida Remane, 1925

ao and Clausen, 1970 AO, aO, Ao, or ao may refer to: Arts and entertainment * Adults Only, an entertainment rating * AO Music (AOmusic), a world-music fusion group consisting of Jay Oliver, Miriam Stockley and others * Ao: The Last Hunter, a 2010 prehistoric ...

/small> *Family Cephalodasyidae Hummon & Todaro, 2010 ::*Genus '' Cephalodasys'' Remane, 1926 ::*Genus '' Dolichodasys'' Gagne, 1977 ::*Genus '' Megadasys'' Schmidt, 1974 ::*Genus ''

Mesodasys ''Mesodasys'' is a genus of gastrotrichs belonging to the family Cephalodasyidae. The species of this genus are found in Europe. Species: *''Mesodasys adenotubulatus'' *''Mesodasys brittanica'' *''Mesodasys hexapodus'' *''Mesodasys ischien ...

'' Remane, 1951 ::*Genus ''

Paradasys ''Paradasys'' is a genus of gastrotrichs belonging to the family Cephalodasyidae. The species of this genus are found in Northern Europe, India. Species: *'' Paradasys bilobocaudus'' *'' Paradasys hexadactylus'' *'' Paradasys lineatus'' *' ...

'' Remane, 1934 ::*Genus '' Pleurodasys'' Remane, 1927 *Family

Dactylopodolidae Dactylopodolidae is a family of worms belonging to the order Macrodasyida Macrodasyida is an order (biology), order of gastrotrichs. Members of this order are somewhat worm-like in form, and not more than 1 to 1.5 mm in length. Macrodasyi ...

Strand, 1929 ::*Genus '' Dactylopodola'' Strand, 1929 ::*Genus '' Dendrodasys'' Wilke, 1954 ::*Genus '' Dendropodola'' Hummon, Todaro & Tongiorgi, 1992 *Family

Lepidodasyidae Lepidodasyidae is a family of worms belonging to the order Macrodasyida Macrodasyida is an order (biology), order of gastrotrichs. Members of this order are somewhat worm-like in form, and not more than 1 to 1.5 mm in length. Macrodasyids ...

Remane, 1927 ::*Genus '' Lepidodasys'' Remane, 1926 *Family

Macrodasyidae Macrodasyidae is a family of worms belonging to the order Macrodasyida Macrodasyida is an order (biology), order of gastrotrichs. Members of this order are somewhat worm-like in form, and not more than 1 to 1.5 mm in length. Macrodasyids ...

Remane, 1926 ::*Genus ''

Macrodasys ''Macrodasys'' is a genus of gastrotrichs belonging to the family Macrodasyidae Macrodasyidae is a family of worms belonging to the order Macrodasyida Macrodasyida is an order (biology), order of gastrotrichs. Members of this order are somewh ...

'' Remane, 1924 ::*Genus '' Urodasys'' Remane, 1926 *Family

Planodasyidae Planodasyidae is a family of worms belonging to the order Macrodasyida Macrodasyida is an order (biology), order of gastrotrichs. Members of this order are somewhat worm-like in form, and not more than 1 to 1.5 mm in length. Macrodasyids ...

Rao & Clausen, 1970 ::*Genus '' Crasiella'' Clausen, 1968 ::*Genus '' Planodasys'' Rao & Clausen, 1970 *Family

Redudasyidae Redudasyidae is a family of worms belonging to the order Macrodasyida Macrodasyida is an order (biology), order of gastrotrichs. Members of this order are somewhat worm-like in form, and not more than 1 to 1.5 mm in length. Macrodasyids a ...

Todaro, Dal Zotto, Jondelius, Hochberg et al., 2012 ::*Genus '' Anandrodasys'' Todaro, Dal Zotto, Jondelius, Hochberg et al., 2012 ::*Genus '' Redudasys'' Kisielewski, 1987 *Family Thaumastodermatidae Remane, 1927 **Subfamily Diplodasyinae Ruppert, 1978 ***Genus ''

Acanthodasys ''Acanthodasys'' is a genus of worms belonging to the family Thaumastodermatidae Thaumastodermatidae is a family of worms belonging to the order Macrodasyida. Subfamilies and genera Subfamilies and genera: *Diplodasyinae Ruppert, 1978 **''Acant ...

'' Remane, 1927 ***Genus ''

Diplodasys ''Diplodasys'' is a genus of worms belonging to the family Thaumastodermatidae Thaumastodermatidae is a family of worms belonging to the order Macrodasyida. Subfamilies and genera Subfamilies and genera: *Diplodasyinae Ruppert, 1978 **''Acanth ...

'' Remane, 1927 **Subfamily Thaumastodermatinae Remane, 1927 ***Genus '' Hemidasys'' Claparède, 1867 ***Genus ''

Oregodasys ''Oregodasys'' is a genus of worms belonging to the family Thaumastodermatidae Thaumastodermatidae is a family of worms belonging to the order Macrodasyida. Subfamilies and genera Subfamilies and genera: *Diplodasyinae Ruppert, 1978 **''Acantho ...

'' Hummon, 2008 =(Platydasys Remane, 1927) ***Genus ''

Pseudostomella ''Pseudostomella'' is a genus of worms belonging to the family Thaumastodermatidae. The genus has almost cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or mos ...

'' Swedmark, 1956 ***Genus ''

Ptychostomella ''Ptychostomella'' is a genus of gastrotrichs belonging to the family Thaumastodermatidae Thaumastodermatidae is a family of worms belonging to the order Macrodasyida. Subfamilies and genera Subfamilies and genera: *Diplodasyinae Ruppert, 1978 ...

'' Remane, 1926 ***Genus ''

Tetranchyroderma ''Tetranchyroderma'' is a genus of gastrotrichs belonging to the family Thaumastodermatidae. The genus has cosmopolitan distribution. Species Species: *'' Tetranchyroderma aapton'' *''Tetranchyroderma adeleae'' *''Tetranchyroderma aethes ...

'' Remane, 1926 ***Genus ''

Thaumastoderma ''Thaumastoderma'' is a genus of gastrotrichs belonging to the family Thaumastodermatidae. The species of this genus are found in Europe. Species Species: *'' Thaumastoderma antarctica'' *'' Thaumastoderma appendiculatum'' *'' Thaumastode ...

'' Remane, 1926 *Family

Turbanellidae Turbanellidae is a family of worms belonging to the order Macrodasyida. Genera: * '' Desmodasys'' Clausen, 1965 * '' Dinodasys'' Remane, 1927 * '' Marinellina'' Ruttner-Kolisko, 1955 * '' Paraturbanella'' Remane, 1927 * '' Prostobucantia'' Ev ...

Remane, 1927 ::*Genus '' Desmodasys'' Clausen, 1965 ::*Genus '' Dinodasys'' Remane, 1927 ::*Genus ''

Paraturbanella ''Paraturbanella'' is a genus of worms belonging to the family Turbanellidae. The genus has almost cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most of t ...

'' Remane, 1927 ::*Genus '' Prostobuccantia'' Evans & Hummon, 1991 ::*Genus '' Pseudoturbanella'' d'Hondt, 1968 ::*Genus '' Turbanella'' Schultze, 1853 *Family

Xenodasyidae Xenodasyidae is a family of worms belonging to the order Macrodasyida Macrodasyida is an order (biology), order of gastrotrichs. Members of this order are somewhat worm-like in form, and not more than 1 to 1.5 mm in length. Macrodasyids a ...

Todaro, Guidi, Leasi & Tongiorgi, 2006 ::*Genus '' Chordodasiopsis'' Todaro, Guidi, Leasi & Tongiorgi, 2006 ::*Genus '' Xenodasys'' Swedmark, 1967 *''

Incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'' ::*Genus ''

Marinellina ''Marinellina'' is a genus of gastrotrichs belonging to the family Turbanellidae Turbanellidae is a family of worms belonging to the order Macrodasyida. Genera: * '' Desmodasys'' Clausen, 1965 * '' Dinodasys'' Remane, 1927 * '' Marinellina'' ...

'' Ruttner-Kolisko, 1955 Order Chaetonotida Remane, 1925

/small> Suborder

Multitubulatina ''Neodasys'' is a genus of gastrotrichs in the class Chaetonotida. It is the only genus in the family Neodasyidae, which is the only family in the suborder Multitubulatina. Species *''Neodasys chaetonotoideus'' Remane, 1927 *''Neodasys cirritus' ...

d'Hondt, 1971 *Family

Neodasyidae ''Neodasys'' is a genus of gastrotrichs in the class Chaetonotida. It is the only genus in the family Neodasyidae, which is the only family in the suborder Multitubulatina. Species *''Neodasys chaetonotoideus ''Neodasys'' is a genus of gastro ...

Remane, 1929 ::*Genus ''

Neodasys ''Neodasys'' is a genus of gastrotrichs in the class Chaetonotida. It is the only genus in the family Neodasyidae, which is the only family in the suborder Multitubulatina. Species *''Neodasys chaetonotoideus ''Neodasys'' is a genus of gast ...

'' Remane, 1927 Suborder

Paucitubulatina Paucitubulatina is a suborder of gastrotrichs in the order Chaetonotida. Families * Chaetonotidae Gosse, 1864 sensu Leasi & Todaro, 2008Gosse, P. H. (1864). The natural history of the hairy-backed animalcules (Chætonotidæ). ''The Intellectual ...

d'Hondt, 1971 *Family

Chaetonotidae Chaetonotidae is a family of gastrotrichs in the order Chaetonotida. It is the largest family of gastrotrichs with almost 400 species, some of which are marine and some freshwater. Current classification is largely based on shape and external str ...

Gosse, 1864 **Subfamily Chaetonotinae Kisielewski, 1991 ***Genus '' Arenotus'' Kisielewski, 1987 ***Genus ''

Aspidiophorus ''Aspidiophorus'' is a genus of gastrotrichs belonging to the family Chaetonotidae Chaetonotidae is a family of gastrotrichs in the order Chaetonotida. It is the largest family of gastrotrichs with almost 400 species, some of which are marine ...

'' Voigt, 1903 ***Genus '' Caudichthydium'' Schwank, 1990 ***Genus ''

Chaetonotus ''Chaetonotus'' is a genus of gastrotrichs in the family Chaetonotidae Chaetonotidae is a family of gastrotrichs in the order Chaetonotida. It is the largest family of gastrotrichs with almost 400 species, some of which are marine and some fre ...

'' Ehrenberg, 1830 ***Genus ''

Fluxiderma ''Fluxiderma'' is a genus of gastrotrichs belonging to the family Chaetonotidae Chaetonotidae is a family of gastrotrichs in the order Chaetonotida. It is the largest family of gastrotrichs with almost 400 species, some of which are marine and ...

'' d'Hondt, 1974 ***Genus ''

Ichthydium ''Ichthydium'' is a genus of gastrotrichs belonging to the family Chaetonotidae Chaetonotidae is a family of gastrotrichs in the order Chaetonotida. It is the largest family of gastrotrichs with almost 400 species, some of which are marine and ...

'' Ehrenberg, 1830 ***Genus ''

Halichaetonotus ''Halichaetonotus'' is a genus of gastrotrichs belonging to the family Chaetonotidae. The species of this genus are found in Europe and Central America. Species Species: *''Halichaetonotus aculifer'' *''Halichaetonotus arenarius'' *''Halic ...

'' Remane, 1936 ***Genus ''

Heterolepidoderma ''Heterolepidoderma'' is a genus of gastrotrichs belonging to the family Chaetonotidae. The species of this genus are found in Europe and Southern America. Species: * ''Heterolepidoderma acidophilum'' Kanneby, Todaro & Jondelius, 2012 * ''Heter ...

'' Remane, 1927 ***Genus '' Lepidochaetus'' Kisielewski 1991 ***Genus ''

Lepidodermella ''Lepidodermella'' is a genus of gastrotrichs belonging to the family Chaetonotidae Chaetonotidae is a family of gastrotrichs in the order Chaetonotida. It is the largest family of gastrotrichs with almost 400 species, some of which are marine ...

'' Blake, 1933 ***Genus ''

Polymerurus ''Polymerurus'' is a genus of gastrotrichs belonging to the family Chaetonotidae. The genus has almost cosmopolitan distribution In biogeography, cosmopolitan distribution is the term for the range of a taxon that extends across all or most ...

'' Remane, 1927 ***Genus ''

Rhomballichthys ''Rhomballichthys'' is a genus of gastrotrichs belonging to the family Chaetonotidae Chaetonotidae is a family of gastrotrichs in the order Chaetonotida. It is the largest family of gastrotrichs with almost 400 species, some of which are marin ...

'' Schwank, 1990 **Subfamily Undulinae Kisielewski 1991 ***Genus '' Undula'' Kisielewski 1991 *Family Dasydytidae Daday, 1905 ::*Genus '' Anacanthoderma'' Marcolongo, 1910 ::*Genus '' Chitonodytes'' Remane, 1936 ::*Genus '' Dasydytes'' Gosse, 1851 ::*Genus '' Haltidytes'' Remane 1936 ::*Genus '' Ornamentula'' Kisielewski 1991 ::*Genus '' Setopus'' Grünspan, 1908 ::*Genus '' Stylochaeta'' Hlava, 1905 *Family

Dichaeturidae Dichaeturidae is a family of worms belonging to the order Chaetonotida. Genera: * ''Dichaetura'' Lauterborn, 1913 * ''Marinellina ''Marinellina'' is a genus of gastrotrichs belonging to the family Turbanellidae Turbanellidae is a family of ...

Remane, 1927 ::*Genus ''

Dichaetura ''Dichaetura'' is a genus of gastrotrichs The gastrotrichs (phylum Gastrotricha), commonly referred to as hairybellies or hairybacks, are a group of microscopic (0.06-3.0 mm), worm-like, acoelomate animals, and are widely distributed and ...

'' Lauterborn, 1913 *Family

Muselliferidae Muselliferidae is a family of worms belonging to the order Chaetonotida. Genera: * '' Diuronotus'' Todaro, Balsamo & Kristensen, 2005 * ''Musellifer ''Musellifer'' is a genus of gastrotrichs The gastrotrichs (phylum Gastrotricha), commonly ...

Leasi & Todaro, 2008 ::*Genus ''

Diuronotus ''Diuronotus'' is a genus of gastrotrichs belonging to the family Muselliferidae. The species of this genus are found in Scandinavia and Greenland. Species: *''Diuronotus aspetos ''Diuronotus aspetos'' is a species of large sized meiofaunal ...

'' Todaro, Kristensen & Balsamo, 2005 ::*Genus ''

Musellifer ''Musellifer'' is a genus of gastrotrichs The gastrotrichs (phylum Gastrotricha), commonly referred to as hairybellies or hairybacks, are a group of microscopic (0.06-3.0 mm), worm-like, acoelomate animals, and are widely distributed and ...

'' Hummon, 1969 *Family

Neogosseidae Neogosseidae is a family of worms belonging to the order Chaetonotida The Chaetonotida is an order of gastrotrichs. They generally have a tenpin or bottle-like shape. Chaetonotids inhabit both freshwater and marine environments. They can be ...

Remane, 1927 ::*Genus '' Neogossea'' Remane, 1927 ::*Genus '' Kijanebalola'' Beauchamp, 1932 *Family

Proichthydiidae Proichthydiidae is a family of worms belonging to the order Chaetonotida The Chaetonotida is an order of gastrotrichs. They generally have a tenpin or bottle-like shape. Chaetonotids inhabit both freshwater and marine environments. They can b ...

Remane, 1927 ::*Genus '' Proichthydium'' Cordero, 1918 ::*Genus '' Proichthydioides'' Sudzuki, 1971 *Family

Xenotrichulidae Xenotrichulidae is a family of worms belonging to the order Chaetonotida The Chaetonotida is an order of gastrotrichs. They generally have a tenpin or bottle-like shape. Chaetonotids inhabit both freshwater and marine environments. They can b ...

Remane, 1927 **Subfamily Draculiciterinae Ruppert, 1979 ***Genus '' Draculiciteria'' Hummon, 1974 **Subfamily Xenotrichulinae Remane, 1927 ***Genus '' Heteroxenotrichula'' Wilke, 1954 ***Genus '' Xenotrichula'' Remane, 1927

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Gastrotrichs
in the

Encyclopedia of Life The ''Encyclopedia of Life'' (''EOL'') is a free, online encyclopedia intended to document all of the 1.9 million living species known to science. It is compiled from existing trusted databases curated by experts and with the assistance of no ...

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