/. CRUSTACEA: PnrLLOPOD A. 



415 



little knowledge of but one species, and this with its single pair 

 of antennae differs from all recent Crustacea. 



Fio. 416. Fig. 417. 



Fig. 416. — Paradoxides bohemicus. (From Zittel.) 



Fig. 417. — Triarthrus becki, ventral surface, restored. (After Beecher.) The head 

 bears one pair of antenna and four pairs of biramous feet, the basal joints serv- 

 ing as maxillae. Trunlc with biramous feet. 



Sulj Class II. Phyllopoda. 



The Phyllopoda are clearly the most jjrimitive of Crustacea. 

 The name is derived from the leaf-like feet (p. 410), which occur 

 upon the thoracic region. More anteriorly the ai^pendages are 

 schizopodal, the second pair of antenna often being efficient swim- 

 ming organs. The number of body segments varies between very 

 wide limits, there being less than a dozen in the C'ladocera, while, 

 if Savigny's law (p. 401) holds true, there are over sixty in some 

 Apodidaj. In most forms (the Branchipodids excepted) a cara- 

 pace is developed by a backward growth from the head. This 

 forms a broad oval shell covering most of the body in the Apodidaj 

 (fig. 41:2); in the Estheriidaj and Cladocera it is divided into right 

 and left halves hinged together in the mid-dorsal line, thus giving 

 these animals the appearance of bivalve molluscs. 



These forms have, besides the unpaired nauj^lius eye, a piair of 

 compound eyes which in the compressed forms are frequently 

 fused, although distinct in the young and retaining the double 



