58 



GENERAL ZOOLOGY 



tremely variable, the number of body segments ranging 

 from four to thirty-one. Antennae, compound eyes, and 

 biramous appendages were present. All trilobites were 

 marine and none have been alive for the past several 

 million years. Recent Crustacea are classified as follows : 



DiHerogammarus Combarus Ca/linectes 



FIG. 31. Examples of the Class Crustacea. 



Subclass I. Entomostraca. Number of metameres variable; kidney 

 opens in base of maxillae; no gastric mill in stomach. 



Order 1. PHYLLOPODA. With ten to thirty pairs of leaf -like 



feet; a carapace often present. Examples: Eubranchipus, 



Estheria (Fig. 31). 

 Order 2. CLADOCERA. Second antenna? large, biramous, and 



used for swimming; body usually enclosed in a bivalve shell. 



Examples: Daphnia, Bosmina (Fig. 31). 

 Order 3. OSTRACODA. Only seven pairs of appendages. Body 



completely enclosed in a bivalve shell. Example: Cypris 



(Fig. 32). 



