294 COLLEGE ZOOLOGY 



Order 2. Cladocera. — Small Braxchiopoda with bodies 

 usually enclosed in a bivalve shell, large second anten- 

 nae used in swimming, and four to six pairs of swimming 

 feet. Examples: Daphnia (Fig. 211), Leptodora. 

 Subclass II. Ostracoda. — Small, laterally compressed Crus- 

 tacea entirely enclosed in a bivalve shell. Usually seven 

 pairs of appendages. Examples: Cypris (Fig. 212), 

 Candona. 

 Subclass III. Copepoda. Elongated Crustacea with bira- 

 mous shimming feet, without shell, and without ab- 

 dominal appendages. Examples: Cyclops (Fig. 213), Can- 

 thocamptus, Diaptomus, Arguhis, Sapphirina, Achtheres. 

 Subclass IV. Cirripedia. — Crustacea usually fixed or para- 

 sitic, with indistinctly segmented body enclosed in a 

 carapace. Often greatly modified because of fixed or 

 parasitic habit. Examples: Lepas, Balanus (Fig. 214), 

 Sacculina, Peltogaster. 

 Subclass V. Malacostraca. — Crustacea usually of large 

 size, with five segments in the head, eight in the thorax, 

 and six in the abdomen, and with a gastric mill in the 

 stomach. 



Order 1. Nebaliacea. — Small, shrimp-like Malacostraca 

 with head and middle portion of body enclosed in a 

 bivalve shell, with eight thoracic segments, eight abdom- 

 inal segments, and a terminal caudal fork. Example: 

 Xebalia (Fig. 215). 



Order 2. Anaspidacea. — Malacostraca with distinct 

 thoracic segments, pedunculate eyes, and no carapace. 

 Example : A naspides. 



Order 3. Mysidacea. — Malacostraca of small size, with 

 biramous antennules, thoracic limbs with natatory exopo- 

 dites, and a large carapace. Example: Mysis (Fig. 217). 



Order 4. Cumacea. — Malacostraca with a slender ab- 

 domen, four or five free thoracic segments, and a small 

 carapace. Example: Diastylis (Fig. 218). 



