CRUSTACEA 59 



Order 4. COPEPODA. With large uniramous antennae which are 

 used for swimming; abdomen without metameric appendages. 

 Examples: Cyclops (Fig. 31), Diaptomus. 



Order 5. CIRRIPEDIA. Fixed or parasitic; body enclosed in a 

 calcareous, non-metameric shell; barnacles. Example: 

 Balanus (Fig. 31). 



Subclass 2. Malacostraca. Usually of large size; with five metameres 

 in the head, eight in the thorax, and six in the abdomen; with a 

 grinding apparatus, the gastric-mill, in the stomach. 



Order 6. NEBALIACEA. Small shrimp-like, marine crustaceans, 

 with an extra metamere in the abdomen; carapace well 

 developed. 



Order 7. ANASPIDACEA. With distinct thoracic segments, 

 stalked eyes, and no carapace. 



Order 8. MYSIDACEA. Small shrimp-like crustaceans; with 

 biramous thoracic legs, and a large carapace. 



Order 9. CUMACEA. Malacostraca without abdominal append- 

 ages, with a small carapace and four or five free thoracic 

 segments. 



Order 10. TANAIDACEA. Malacostraca with all but two thoracic 

 segments free; respiratory chambers on sides of thorax. 



Order 11. ISOPODA. Body usually broad and flat; no carapace; 

 seven free thoracic segments. Examples: Asellus, Porcellio 

 (Fig. 31). 



Order 12. AMPHIPODA. Body usually laterally compressed; 

 with seven free thoracic segments; usually with three pairs 

 of appendages fitted for jumping at the posterior end. 

 Example: Dikerogammarus (Fig. 31). 



Order 13. EUPHAUSIACEA. Thorax covered by carapace; with 

 respiratory chambers at sides; no thoracic legs serve as 

 mouth parts. 



Order 14. DEC APOD A. With first three pairs of thoracic ap- 

 pendages specialized as mouth parts; ten walking legs; 

 carapace covers thorax; stalked eyes. 



Suborder 1. Natantia. Slender, laterally compressed; ab- 

 domen well developed and provided with appendages. Ex- 

 amples: Cambarus (Fig. 31), lobster, shrimps, prawns. 

 Suborder 2. Reptantia. Flattened, short; abdomen small and 

 folded forward under thorax. Examples: Callinectes (Fig. 

 31), crabs. 



Order 15. STOMATOPODA. Five pairs of thoracic limbs serve as 

 mouth parts; six biramous walking legs; carapace covers 

 only part of thorax. 



