504 



CRUSTACEA. 



valve is marked by a tubercle, pit, or group of spots, or by both spots 

 and a pit. There are seven pairs of appendages, of which the first 

 two are ante?ince, and the posterior appendages are adapted for creeping 

 or swimming. 



The Ostracoda are all small Crustaceans in which the body is 

 enclosed within a bean-shaped or mussel-shaped shell, composed of 

 two valves united along the back by an elastic ligament (fig. 360, b). 

 The animal can open the valves of the shell along their ventral 

 margin, and can protrude the appendages and the caudal extremity 

 of the abdomen. The first two pairs of appendages are antennules 



Fig. 360. — Recent Ostracoda. a, Cyftridiua Mcssincnsis, viewed from the side, and greatly 

 enlarged, one-half of the shell being removed, b, Cypris fusca, viewed from the side, and less 

 highly magnified, the shell-valves being retained, but slightly displaced, a, Antennules ; an, 

 Antennae ; o, Eye ; o' , Ocellus; c, Heart ; s, Stomach ; f, Whip-like appendage for the retention 

 of the brood ; ad, Extremity of the abdomen ; m, Mandibular appendage ; mx, The first, second, 

 and third maxillae. 



and antennae (fig. 360, a), which can be used as locomotive limbs. 

 These are followed by a pair of mandibles, succeeded by a pair of 

 maxillse ; and the next two pairs of appendages may be either jaws 

 or legs. The sixth and seventh pairs of appendages are leg-like, 

 and variously formed in different cases. A median eye, or two 

 lateral eyes are present. Branchial plates are attached to some of 

 the jaws, and a distinct heart may be present (Cypridina) or absent 

 (Cypris and Cy there). The young forms are usually " nauplii," but 



