L CRUSTACEA: PHTLLOPODA. 



415 



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

 of antennae differs from all recent Crustacea. 



FIG. 416. FIG. 417. 



FIG. 416. Paradoxides bohemicus. (From Zittel.) 



FIG. W.Triarthru* becki, ventral surface, restored. (After Beecher.) The head 

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

 ing as maxillae. Trunk with biramous feet. 



Sub Class II. Phyllopoda. 



The Phyllopoda are clearly the most primitive of Crustacea. 

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

 upon the thoracic region. More anteriorly the appendages are 

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

 ming organs. The number of body segments varies between very 

 wide limits, there being less than a dozen in the Cladocera, while, 

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

 Apodidae. In most forms (the Branchipodidae 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 Apodidae 

 (fig. 412); in the Estheriidae 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 nauplius eye, a pair of 

 compound eyes which in the compressed forms are frequently 

 fused, although distinct in the young and retaining the double 



