Ascothoracida is a small group of

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...

s, comprising around 100 species. They are found throughout the world, and are

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...

s on

cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that ...

ns and

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the s ...

s. Ascothoracida was previously

ranked A ranking is a relationship between a set of items such that, for any two items, the first is either "ranked higher than", "ranked lower than" or "ranked equal to" the second. In mathematics, this is known as a weak order or total preorder of ...

as an order within the

infraclass In biological classification, class ( la, classis) is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank. It is a group of related taxonomic orders. Other well-known ranks in descending order of size are life, domain, kingdo ...

Cirripedia ( barnacles), but now both Ascothoracida and Cirripedia are considered separate subclasses. Those two subclasses, along with

Facetotecta Facetotecta is a poorly known subclass of thecostracan crustaceans. The adult forms have never been recognised, and the group is known only from its larvae, the "y- nauplius" and "y- cyprid" larvae. They are mostly found in the north Atlantic Oc ...

, make up the class

Thecostraca Thecostraca is a Class (biology), class of marine invertebrates containing over 2,200 described species. Many species have planktonic larvae which become Sessility (zoology), sessile or parasite, parasitic as adults. The most important subgroup ...

. The

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...

of Ascothoracida species has six pair of biramous appendages, while the abdomen has four segments and a terminal

telson The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...

with a caudal furca. This arrangement is similar to that seen in copepods. In addition, there is a bivalved carapace, which is expanded in females.

References

External links

* Maxillopoda {{Maxillopoda-stub