CRUSTACEANS 



Animals minute, entirely enclosed in bivalve shells. 



Ostracoda (p. i68). 



2. Orders of Malacostraca 



Carapace absent, body flattened laterally, very often jump- 

 ing animals. Amphipoda (p. 169). 

 Carapace absent (Fig. 131), body flattened dorsoventrally. 



Isopoda (p. 171). 

 Carapace present (Fig. 133), covering the entire thorax. 



Decapoda (p. 172). 



Subclass Entomostraca 



Fairy Shrimps, Water-fleas, Copepods, Ostracods 



These are small, often minute crustaceans which have no 

 appendages on the abdomen. The three most important orders 

 of fresh water entomostracans are the phyllopods, copepods, 

 and ostracods. 



Phyllopods — Phyllopoda 



The Order Phyllopoda includes the Suborder Branchiopoda, 

 the fairy shrimps (p. 163), which are an inch or more long, and 

 the Suborder Cladocera, the water-fleas (p. 164), which are 

 minute. 



Fairy shrimps, Branchiopoda. — Fairy shrimps are about 

 an inch long, varicolored, red, blue, green, and bronze. They 

 are the largest of the entomostracans, distinguished from all 

 the rest by the leaflike appendages which have given them 

 the name Phyllopoda or leaf -footed ones (Fig. 123). These 

 "leaf -feet" are really gill-feet, combined breathing and swim- 

 ming organs borne on the body segments posterior to the head, 

 and although they are true respirator}'- organs, they are re- 

 markable in having "chewing bases" which help manipulate 

 the food. Fairy shrimps always swim on their backs and the 

 waving plumes of their gill-feet are the most conspicuous part 

 of them. The hind part of the body is slender and with- 



161 



