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an order of higher crustaceans. The body varies in length from 5 to 96 mm. Externally the animals resemble shrimp of the order Decapoda, differing from them in having gills that are not covered by a thoracic shield and that are located on the bases of the thoracic extremities. The biramous thoracic extremities are used only for swimming. The eyes are stalk-shaped; there are photophores on the eye stalks, as well as on the bases of several pairs of thoracic limbs and on the first four abdominal segments. The Euphausiacea are dioecious. Eggs are laid in the water. The larva leaves the egg during the nauplius stage, after which several more developmental stages follow; the cycle from egg to adult is completed in three or four months.
The order embraces approximately 90 known species, which are widely distributed in the world ocean, especially in subtropical and tropical regions. The animals reproduce in large numbers in some seas, where they are the source of food for various marine mammals and fishes. In the waters of Antarctica the accumulation of some species of whale is related to the mass reproduction of krill, including one member of the Euphausiacea, Euphasia superba. In the Barents Sea, the mass-reproducing species Thysanoessa raschii is a food source for herring, Eurasian perch, Atlantic cod, and other commercial fishes.
REFERENCESZhizn’ zhivotnykh, vol. 2. Moscow, 1968.
Dogel’, V. A. Zoologiia bespozvonochnykh, 6th ed. Moscow, 1975.
A. V. IVANOV