234 MANUAL OF ZOOLOGY. 



"Animal aquatic, covered with a shell, or carapace, of a 

 horny consistency, formed of one or more pieces, in some 

 genera resembling a cuirass or buckler, and in others a bivalve 

 shell, which completely or in great part envelops the body and 

 limbs of the animal. In other genera the animal is invested 

 with a multivalve carapace, like jointed plate-armour; the 

 branchiae are attached either to the feet or to the organs of 

 mastication ; the limbs are jointed, and more or less setiferous. 

 The animals, for the most part, undergo a regular moulting or 

 change of shell, as they grow ; in some cases this amounts to 

 a species of transformation." 



The Entomostraca are divided into two great divisions, or 

 " legions," the Lophyropoda and the Branchiopoda, with which 

 the order Merostomata may be conveniently considered. 



DIVISION A. LOPHYROPODA. The members of this division 

 possess few branchiae, and these are attached to the appen- 

 dages of the mouth. The feet are few in number, and mainly 

 subserve locomotion ; the carapace is in the form either of 

 a shield protecting the cephalothorax, or of a bivalve shell 

 enclosing the entire body. The mouth is not suctorial, but is 

 furnished with organs of mastication. 



This division comprises the two orders Ostracoda and 

 Copepoda. 



ORDER I. OSTRACODA. Small Crustaceans having the entire 

 body enclosed in a shell or carapace, which is composed of two 

 valves united along the back by a membrane. The branchiae 

 are attached to the posterior jaws, and there are only two or 

 three pairs of feet, which subserve locomotion, but are not 

 adapted for swimming. A distinct heart is sometimes present 

 (Cypridina), but is more usually wanting (Cy/rz'jand Cythere). 



Little is known of the development of the Ostracoda, but the 

 young of Cypris are said to be " shell-bearing Nauplius forms " 

 (Glaus), possessing only the three anterior pairs of limbs, but 

 protected by a bivalve shell. As in other Nauplii, the third 

 pair of limbs, though now locomotive, are ultimately transformed 

 into the mandibles. They pass through several stages, with 

 complete moults, before arriving at sexual maturity. The 

 Cytherides, on the other hand, have at birth the two pairs of 

 antennae and two pairs of jaws, with three pairs of rudimentary 

 abdominal limbs. 



The order includes the Cyprides (fig. 87, a\ which are of 

 almost universal occurrence in fresh water. The common 

 Cypris is completely protected from its enemies by a bivalve 

 carapace, which it can open and shut at will, and out of which 

 it can protrude its feet. The closure of the carapace is effected 



