CRUSTACEA (Crustacea) — the class of animals like arthropods combining 5 subclasses — zhabronogy, tsefalokarid, maksillopod, rakushkovy, highest crayfish. It is known apprx. 20 thousand types (in the USSR St. 2000 types). The ruble — preferential water animals, lives in the seas and fresh reservoirs where they make the ground mass of plankton (see). Some types of R. live on the land (wood lice, sea fleas).
The sizes of a body of R. fluctuate from shares of millimeter to meter (fig). The body at R.'s most is covered with an armor, divided into the head, a breast and an abdomen. On the head two couples of horns (antennas), steam of upper and two couples of mandibles are located. Joints of a breast and an abdomen bear on a pair of legs. Rubles breathe gills. The circulatory system which is not closed is available heart. The nervous system is presented by a nadglotochny ganglion and a belly chain of nerve knots. Sense bodys at many R. are well developed, there are compound eyes, an organ of equilibrium. River, except usonogy and some decapoda of crayfish, a razdelnopola. Fertilization outside. Egg leaves a larva (nauplius), then some other larval stages follows. At some crayfish (vetvistousy, fresh-water shrimps, many decapoda) development direct. R.'s growth is connected with a molt, in time the cut is dumped an old armor.
Some types of R. are edible and serve as object of trade (shrimps, crawfishes, lobsters, spiny lobsters, the Kamchatka crab). Small R. are food of many food fishes (see). The parasitic forms causing diseases of fishes are had. Some R. — intermediate owners of parasites of the person: wide tape-worm (Copepoda crustaceans of the sort Cyclops and Diaptomus), parasitic worm (Copepoda crustaceans of the sort Thermocyclops), pulmonary trematode (fresh-water crabs of Eriocheir japonicus), etc.
Many types of R. which are a part of plankton and a benthos play big biol, a role, filtering and clearing reservoirs of pollution.
Bibliography: Dogel V. A. Zoology of invertebrates, M., 1975; Life of animals, under the editorship of L. A. Zenkevich, t. 2, M., 1968; Ivanov A. V. Trade water invertebrates, M., 1955.
T. A. Zaletayeva.