ZOOLOGY A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z           HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site crustacean A crayfish in a Canadian lake. Image credit: M. Turner A member of the class Crustacea (from the Latin crustaceus, meaning "to have a shell or rind") within the phylum Arthropoda. Crustaceans are invertebrate, generally aquatic, animals, which breathe using gills or through the general surface of the body. They have two pairs of antenna-like appendages in front of the mouth. The head and thorax are usually fused. About 25,000 species of Crustacea have been described. These fall into seven sub-classes: Branchiopoda (Greek, branchion = a fin; podos, genitive of pous = a foot). The branchiopods, of which there are five orders, live mostly in fresh water. Their limbs are flattened and leaf-like. Example: the water fleas. Ostracoda (Greek, ostrakodes = testaceous, resembling a shell). The ostracods are minute clamlike crustaceans, whose body and limbs are completely enclosed in a hinged double-shell (bivalve). There are four orders. Copepoda (Greek, kope = handle, oar; podos, genitive of pous = a foot). The copepods are abundant aquatic crustaceans (indeed, they are the most abundant animals on Earth), which are an important source of food (as plankton) in the sea. Many are parasitic. There are seven orders. Mystacocarida (Greek, mystakos, genitive of mystax = upper lip, moustache; Latin, caridis, genitive of caris = a shrimp). There is one order. Branchiura (Greek, branchia = the gills of fishes). Cirripedia (Latin, cirrus = a curl; pedis, genitive of pes = a foot). The cirripedes are completely sedentary aquatic crustaceans. Many are parasitic. Examples include the barnacles and acorn shells. There are four orders. Malacostraca (Greek, malakos = soft; ostrakon = a shell). These are crustaceans whose bodies are composed of 19 somites, all of which generally have appendages. The thorax has eight parts, and the abdomen has six pairs of limbs. There are six super-orders: Leptostraca (Greek, leptos = small, thin; ostrakon = a shell) or Phyllokarida (Greek, phyllon = a leaf; Latin, caridis, genitive of caris = a shrimp). Marine and mud-burrowers, with an abdomen having seven segments. There is one order. Syncarida (Greek, syn = together; Latin, caridis, genitive of caris = a shrimp). A small freshwater group of which there are two orders. Paercarida (Greek, pera = a pouch). This super-order includes opossum-shrimps, woodlice, the freshwater shrimp, the shore hopper, and the whale louse Hoplocarida (Greek, hoplon = a tool, weapon). The mantis shrimps. There is just one order, which is exclusively marine. Pancarida (Greek, pan = all). There is one order, consisting of minute, blind, creeping crustaceans. Eucarida (Greek, eu- = true). These crustaceans have eyes that are stalked, and a carapace that is fused dorsally with all the thoracic somites. There are two orders, which include krill, prawns, shrimps, crayfish (see illustration), lobsters, and crabs. Related category    • ZOOLOGY Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP