The class Malacostraca comprises three subclasses: Eu-malacostraca, Hoplocarida, and Phyllocarida. The subclass Eumalacostraca comprises the superorders Eucarida, Pancar-ida, Peracarida, and Syncarida. The superorder Eucarida includes the order Decapoda (crabs, lobsters, crayfish, shrimp) and the order Euphausiacea.
There are two families within the order Euphausiacea: Eu-phausiidae and Bentheuphausiidae. Ten genera comprise the family: Euphausiidae Euphausia, Meganyctiphanes, Nematobra-chion, Nematoscelis, Nyctiphanes, Pseudeuphausia, Stylocheiron, Tessarabrachion, Thysanoessa, and Thysanopoda.
There is no fossil record of the order Euphausiacea. Today, the order includes about 85 species, of which five are found in the Antarctic, including the dominant Euphausia superba. The cold-adapted krill has benefited from climate change in the Antarctic, completely replacing the temperate-zone pelagic fishes that inhabited the region in the late Eocene.
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