284 



PH YL UM A K TPIR OPODA . 



outside of the body, being formed by an extension and incurving of the 

 branchiostegite flap described in the crayfish. 



FIG. 135. Ventral aspect of female shore crab. 

 AM., abdomen ; tn.vj>., third maxillipede. 



The large gizzard, the enormous greyish -yellow hepatopancreas, the 

 transparent pericardium, and other organs are readily seen. 



SYSTEMATIC SURVEY OF THE CLASS CRUSTACEA. 



(i) Entomostraca, lower forms. 

 They are usually small and simple. 



The number of segments and ap- 

 pendages is very variable. 



The larva is generally hatched as a 

 simple unsegmented Nauplius. 

 There is no gastric mill. 



i. 1'hyllopoda,- 



' AfiiSy B ranch i- 



PTIS ^ LllCl^4 7 't 111 1 Cl 



(brine-shrimps), 



Daphnia, Moina, 

 Polyphemus. 



2. Ostracoda, Cypris, Cypridina. 



3. Copepoda, Cyclops, Arguhis, 



many parasites. 



4. Cirripedia, acorn - shells and 



barnacles, e.g. Balam/s and 

 Lepas. 



(2) Malacostraca, higher forms. 

 They are usually larger and more 



complex. 

 The head consists of 5, the thorax 



of 8, the abdomen of 6 (7 in 



Leptostraca) segments. 

 The larva is usually higher than a 



Nauplius, 

 There is a gastric mill. 



Leptostraca, e.g. Nebalia. 



TAmphipods (sand- 



Arthrostraca -' h PP ers > etc ')' 



a ' | Isopods (wood- 

 lice, etc.). 



( Ciuna. 

 Squilla. 

 Mysis. 



Shrimp, lobster, 

 crayfish, crab. 



I 



Thoracostraca,- 



