PHYLUM ARTHROPODA 297 



Order 5. Tanaidacea. - - MALACOSTRACA with free thoracic 

 segments except the first two, which are fused with the 

 head and extend on the sides, forming a respiratory 

 chamber. Example: Apscudes (Fig. 219). 



Order 6. Isopoda. -- MALACOSTRACA with a body generally 

 broad and flat, seven free thoracic segments, leaf-like 

 legs, and no carapace. Examples: Asellus (Fig. 220, A), 

 ArmadilHum, Oniscus (Fig. 220, B), Porcellio. 



Order 7. Amphipoda. - - MALACOSTRACA laterally com- 

 pressed, with elongated abdomen bearing three pairs 

 of posteriorly directed springing feet and three pairs of 

 anterior swimming feet, and without a carapace. Exam- 

 ples: Gammarus (Fig. 221, A), Talorchestia (Fig. 216), 

 Caprella (Fig. 221, B). 



Order 8. Euphausiacea. MALACOSTRACA with all thoracic 

 segments covered by carapace, pedunculate eyes, none 

 of thoracic limbs specialized as maxillipeds, and only 

 podobranchiae present. Example: Meganycti phones. 



Order 9. Decapoda. MALACOSTRACA with first three pairs 

 of thoracic limbs specialized as maxillipeds, with five 

 pairs of thoracic walking legs, with generally all of the 

 thoracic segments covered by a carapace, and with 

 stalked, compound eyes. 



Suborder i. NATANTIA. - - DECAPODA with body usually 

 laterally compressed, legs generally slender, and pleopods 

 always present in full number, well developed, and used 

 for swimming. Examples: Penceus, Alpheus, Pal&monetes 

 (Fig. 224), Stenopus. 



Suborder 2. REPTANTIA. - - DECAPODA with body not com- 

 pressed, legs strong, pleopods often reduced or absent, 

 not used for swimming. Examples: Hyas, Cancer, Cal- 

 linectes (Fig. 223), Pinnotheres, Cambarus (Fig. 202), 

 Homarus, Palinurus, Eupagurus, Gelasimus (Fig. 223, B). 



Order 10. Stomatopoda. - - MALACOSTRACA with five pairs 

 of anterior maxillipeds on the thorax, and three pairs of 



