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 Nomenclature ...

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

acoelomate The coelom (or celom) is the main body cavity in most animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, it ...

animal Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually, and go through an ontogenetic stage ...

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 incl ...

and

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military ...

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 " ...

and live within the

periphyton Periphyton is a complex mixture of algae, cyanobacteria, heterotrophic microbes, and detritus that is attached to submerged surfaces in most aquatic ecosystems. The related term Aufwuchs (German "surface growth" or "overgrowth") refers to the col ...

, the layer of tiny organisms and

detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts comm ...

that is found on the

seabed The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most o ...

and the beds of other

water bodies A body of water or waterbody (often spelled water body) is any significant accumulation of water on the surface of Earth or another planet. The term most often refers to oceans, seas, and lakes, but it includes smaller pools of water such as ...

. 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, sand ...

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 and

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike proje ...

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 st ...

. 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 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 development ...

, producing unfertilised eggs, and at least one species is

viviparous Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the ...

. 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 Ilya Ilyich Mechnikov (russian: Илья Ильич Мечников; – 15 July 1916), also spelled Élie Metchnikoff, was a Russian zoologist best known for his pioneering research in immunology. Belkin, a Russian science historian, explain ...

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

Rotifer The rotifers (, from the Latin , "wheel", and , "bearing"), commonly called wheel animals or wheel animalcules, make up a phylum (Rotifera ) of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John H ...

a, or the

Nematoda The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...

. On the other hand,

genetic studies Genetic analysis is the overall process of studying and researching in fields of science that involve genetics and molecular biology. There are a number of applications that are developed from this research, and these are also considered parts of ...

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, unsegm ...

, 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 phylogenetic ...

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 Symmetry in biology refers to the symmetry observed in organisms, including plants, animals, fungi, and bacteria. External symmetry can be easily seen by just looking at an organism. For example, take the face of a human being which has a pl ...

, with a transparent strap-shaped or

bowling pin Bowling pins (historically also known as skittles or kegels) are the target of the bowling ball in various bowling games including tenpins, five-pins, duckpins and candlepins. Tenpins Pin specifications are set by the United States Bowling ...

-shaped body, arched dorsally and flattened ventrally. The

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Th ...

end is not clearly defined as a head but contains the sense organs, brain and pharynx.

Cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike proje ...

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 A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

, an

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

and longitudinal and circular bands of muscle fibres. In some primitive species, each epidermal cell has a single cilium, a feature shared only by the gnathostomulans. 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 The coelom (or celom) is the main body cavity in most animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, ...

(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 tiss ...

. In the macrodasyidans, Y-shaped cells, each containing a

vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic m ...

, surround the gut and may function as a

hydrostatic skeleton A hydrostatic skeleton, or hydroskeleton, is a flexible skeleton supported by fluid pressure. Hydrostatic skeletons are common among simple invertebrate organisms. While more advanced organisms can be considered hydrostatic, they are sometimes refe ...

. The mouth is at the anterior end and opens into an elongated muscular

with a triangular or Y-shaped lumen, lined by

myoepithelial cells Myoepithelial cells (sometimes referred to as myoepithelium) are cells usually found in glandular epithelium as a thin layer above the basement membrane but generally beneath the luminal cells. These may be positive for alpha smooth muscle actin ...

. The pharynx opens into a cylindrical intestine, which is lined with glandular and digestive cells. The

anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, ...

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 fro ...

of any excess water swallowed while feeding. In the chaetonotidans, the excretory system consists of a single pair of

protonephridia The nephridium (plural ''nephridia'') is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidneys (which originated from the chordate nephridia). Nephridia remove metabolic wastes from an animal's body. Neph ...

, 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 Metabolic wastes or excrements are substances left over from metabolic processes (such as cellular respiration) which cannot be used by the organism (they are surplus or toxic), and must therefore be excreted. This includes nitrogen compounds, ...

is probably excreted through the body wall, as part of respiration, and the protonephridia are believed to function mainly in

osmoregulation Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration o ...

. 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 A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

. 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 A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympathe ...

, one on either side of the pharynx, connected by a

commissure A commissure () is the location at which two objects abut or are joined. The term is used especially in the fields of anatomy and biology. * The most common usage of the term refers to the brain's commissures, of which there are five. Such a commi ...

. 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

mechanoreceptor A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, a ...

s. There are also ciliated pits on the head, simple ciliary photoreceptors and fleshy appendages which act as

chemoreceptor A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance (endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorecept ...

Distribution and habitat

Gastrotrichs are

cosmopolitan Cosmopolitan may refer to: Food and drink * Cosmopolitan (cocktail), also known as a "Cosmo" History * Rootless cosmopolitan, a Soviet derogatory epithet during Joseph Stalin's anti-Semitic campaign of 1949–1953 Hotels and resorts * Cosmopoli ...

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 under ...

. When pools dry up they can survive periods of desiccation as eggs, and some species are capable of forming

cysts A cyst is a closed sac, having a distinct envelope and division compared with the nearby tissue. Hence, it is a cluster of cells that have grouped together to form a sac (like the manner in which water molecules group together to form a bubble) ...

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

nematode The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant- parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a bro ...

s 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

detritivore Detritivores (also known as detrivores, detritophages, detritus feeders, or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrate ...

s and are microphagous, sucking dead or living organic material,

diatoms A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

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 mo ...

ns and other small macrofauna. Like many microscopic animals, gastrotrich locomotion is primarily powered by

hydrostatics Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...

, 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 The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

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

gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sp ...

s, the anterior portion of which contains

sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, ...

-producing cells and the posterior portion producing ova. The sperm is sometimes packaged in

spermatophore A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophore ...

s and is released through male

gonopore A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrates. Hexapods, including insects have a single common gonopore, except mayflies, which have a pair of gonopores. More specifically, in the unmodified female it is t ...

s that open, often temporarily, on the underside of the animal, roughly two-thirds of the way along the body. A

copulatory organ A sex organ (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...

on the tail collects the sperm and transfers it to the partner's

seminal receptacle Female sperm storage is a biological process and often a type of sexual selection in which sperm cells transferred to a female during mating are temporarily retained within a specific part of the reproductive tract before the oocyte, or egg, is f ...

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 me ...

s, development of the embryo is determinate, with each cell destined to become a specific part of the animal's body. At least one species of gastrotrich, '' Urodasys viviparus'', is

. 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 Uni ...

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

desiccation Desiccation () is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic (attracts and holds water) substance that induces or sustains such a state in its local vicinity in a moderately sealed container. ...

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 Marine larval ecology is the study of the factors influencing dispersing larvae, which many marine invertebrates and fishes have. Marine animals with a larva typically release many larvae into the water column, where the larvae develop before met ...

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 Eutelic organisms have a fixed number of somatic cells when they reach maturity, the exact number being relatively constant for any one species. This phenomenon is also referred to as cell constancy. Development proceeds by cell division until matur ...

, 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/small> *Family

Cephalodasyidae Cephalodasyidae is a family of worms belonging to the order Macrodasyida. Genera: * '' Cephalodasys'' Remane, 1926 * '' Dolichodasys'' Gagne, 1977 * ''Mesodasys ''Mesodasys'' is a genus of gastrotrichs belonging to the 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 Cephalodasyidae is a family of worms belonging to the order Macrodasyida. Genera: * '' Cephalodasys'' Remane, 1926 * '' Dolichodasys'' Gagne, 1977 * ''Mesodasys ...

'' Remane, 1951 ::*Genus ''

Paradasys ''Paradasys'' is a genus of gastrotrichs belonging to the family Cephalodasyidae Cephalodasyidae is a family of worms belonging to the order Macrodasyida. Genera: * '' Cephalodasys'' Remane, 1926 * '' Dolichodasys'' Gagne, 1977 * ''Mesodasys ...

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

Dactylopodolidae Dactylopodolidae is a family of worms belonging to the order Macrodasyida Macrodasyida is an 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 are almost i ...

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 of gastrotrichs. Members of this order are somewhat worm-like in form, and not more than 1 to 1.5 mm in length. Macrodasyids are almost in ...

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

Macrodasyidae Macrodasyidae is a family of worms belonging to the order Macrodasyida Macrodasyida is an 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 are almost in e ...

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

Planodasyidae Planodasyidae is a family of worms belonging to the order Macrodasyida Macrodasyida is an 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 are almost in e ...

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 of gastrotrichs. Members of this order are somewhat worm-like in form, and not more than 1 to 1.5 mm in length. Macrodasyids are almost in en ...

Todaro, Dal Zotto, Jondelius, Hochberg et al., 2012 ::*Genus '' Anandrodasys'' Todaro, Dal Zotto, Jondelius, Hochberg et al., 2012 ::*Genus '' Redudasys'' Kisielewski, 1987 *Family

Thaumastodermatidae Thaumastodermatidae is a family of worms belonging to the order Macrodasyida. Subfamilies and genera Subfamilies and genera: * Diplodasyinae Ruppert, 1978 **'' Acanthodasys'' Remane, 1927 **'' Diplodasys'' Remane, 1927 * Thaumastodermatinae Reman ...

Remane, 1927 **Subfamily Diplodasyinae Ruppert, 1978 ***Genus '' Acanthodasys'' Remane, 1927 ***Genus '' Diplodasys'' Remane, 1927 **Subfamily Thaumastodermatinae Remane, 1927 ***Genus '' Hemidasys'' Claparède, 1867 ***Genus '' Oregodasys'' Hummon, 2008 =(Platydasys Remane, 1927) ***Genus '' Pseudostomella'' Swedmark, 1956 ***Genus '' Ptychostomella'' Remane, 1926 ***Genus ''

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

'' 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'' *''Thaumastoderm ...

'' Remane, 1926 *Family

Turbanellidae Turbanellidae is a family of worms belonging to the order Macrodasyida Macrodasyida is an 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 are almost in e ...

Remane, 1927 ::*Genus '' Desmodasys'' Clausen, 1965 ::*Genus '' Dinodasys'' Remane, 1927 ::*Genus '' Paraturbanella'' 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 of gastrotrichs. Members of this order are somewhat worm-like in form, and not more than 1 to 1.5 mm in length. Macrodasyids are almost in en ...

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'' Ruttner-Kolisko, 1955 Order Chaetonotida Remane, 1925 ao and Clausen, 1970/small> Suborder Multitubulatina d'Hondt, 1971 *Family Neodasyidae 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 Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean ...

'' Remane, 1927 Suborder

Paucitubulatina Paucitubulatina is a suborder of gastrotrichs in 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 ...

d'Hondt, 1971 *Family Chaetonotidae Gosse, 1864 **Subfamily Chaetonotinae Kisielewski, 1991 ***Genus '' Arenotus'' Kisielewski, 1987 ***Genus '' Aspidiophorus'' Voigt, 1903 ***Genus '' Caudichthydium'' Schwank, 1990 ***Genus '' Chaetonotus'' Ehrenberg, 1830 ***Genus '' Fluxiderma'' d'Hondt, 1974 ***Genus '' Ichthydium'' 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'' *'' H ...

'' Remane, 1936 ***Genus '' Heterolepidoderma'' Remane, 1927 ***Genus '' Lepidochaetus'' Kisielewski 1991 ***Genus '' Lepidodermella'' Blake, 1933 ***Genus '' Polymerurus'' Remane, 1927 ***Genus '' Rhomballichthys'' 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 Remane, 1927 ::*Genus '' Dichaetura'' Lauterborn, 1913 *Family Muselliferidae Leasi & Todaro, 2008 ::*Genus '' Diuronotus'' Todaro, Kristensen & Balsamo, 2005 ::*Genus '' Musellifer'' Hummon, 1969 *Family Neogosseidae Remane, 1927 ::*Genus '' Neogossea'' Remane, 1927 ::*Genus '' Kijanebalola'' Beauchamp, 1932 *Family Proichthydiidae Remane, 1927 ::*Genus '' Proichthydium'' Cordero, 1918 ::*Genus '' Proichthydioides'' Sudzuki, 1971 *Family Xenotrichulidae 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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External links

Gastrotrichs
in the

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