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ENTOMOSTRACA

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Originally appearing in Volume V09, Page 656 of the 1911 Encyclopedia Britannica.
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ENTOMOSTRACA . This zoological See also:

term, as now restricted, includes the See also:Branchiopoda, Ostracoda and Copepoda. The Ostracoda have the See also:body enclosed in a bivalve See also:shell-covering, and normally unsegmented. The Branchiopoda have a very variable number of body-segments, with or without a See also:shield, See also:simple or bivalved, and some of the postoral appendages normally branchial. The Copepoda have normally a segmented body, not enclosed in a bivalved shell-covering, the segments not exceeding eleven, the limbs not branchial. Under the heading See also:CRUSTACEA the Entomostraca have already been distinguished not only from the See also:Thyrostraca or Cirripedes, but also from the See also:Malacostraca, and an intermediate See also:group of which the true position is still disputed. The choice is open to maintain the last as an See also:independent subclass, and to follow Claus in calling it the Leptostraca, or to introduce it among the Malacostraca as the Nebaliacea, or with -Packard and Sam to make it an entomostracan subdivision under the See also:title Phyllocarida. At See also:present it comprises the single See also:family Nebaliidae. The bivalved See also:carapace has a jointed rostrum, and covers only the front See also:part of the body, to which it is only attached quite in front, the See also:valve-like sides being under See also:control of an adductor muscle. The eyes are stalked and movable. The first antennae have a lamellar appendage at the end of the peduncle, a decidedly non-entomostracan feature. The second antennae, mandibles and two pairs of maxillae may also be claimed as of malacostracan type.

To these succeed eight pairs of foliaceous branchial appendages on the front See also:

division of the body, followed on the See also:hind division by four pairs of powerful bifurcate See also:swimming feet and two rudimentary pairs, the number, though not the nature, of these appendages being malacostracan. On the other See also:hand, the two limbless segments that precede the caudal furca are decidedly non-malacostracan. The family was See also:long limited to the single genus Nebalia (Leach), and the single See also:species N. bipes (O. See also:Fabricius). Recently Sars has added a See also:Norwegian species, N. typhlops, not See also:blind but weak-eyed. There are also now two more genera, Paranebalia (Claus, 188o), in which the branchialfeet are much longer than in Nebalia, and Nebaliopsis (Sars, 1887), in which they are much shorter. All the species are marine.

End of Article: ENTOMOSTRACA

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