CLASSIFICATION OF CRUSTACEA 



339 



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 diverse. 



The larva is generally hatched as a 

 simple unsegmented Nauplius. 



There is no gastric mill. 



The excretory organ is associated 

 with the second maxillae. 



(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 often a gastric mill. 



The excretory organ is usually 

 associated with the antennae, 

 but maxillary glands may be 

 present in the larvae, and may 

 even persist in adults. 



First Sub-Class. Entomostraca 



Order i. Branchiopoda. — In these at least four pairs of leaf-like swim- 



ming feet bear respiratory plates 

 segmented, and is protected by 

 a shield-Uke or bivalve shell. 

 The mandibles are without 

 palps, and the maxillce are 

 rudimentary. 

 {a) Phyllopoda. The body has 

 numerous segments and (10- 

 20 or more) fohaceous ap- 

 pendages with respiratory 

 plates. The shell is rarely 

 absent, usually shield-like or 

 bivalved. The heart is a 

 long dorsal vessel with 

 numerous openings. The 

 eggs can survive prolonged 

 desiccation in the mud. 

 Branchipus, a beautifully 

 colovured fresh - water 

 form, with hardly any 

 shell. 

 A rtemia, Brine - shrimps. 

 Periodically partheno- 

 genetic. Artemia fertilis 

 is one of the four 

 animals known to occur 

 in the dense waters of 

 Salt Lake. 

 A pus, an archaic fresh- 

 water form with a large 

 dorsal shield. 



The body is generally well 



Fig. 184. — Dorsal surface of Apus 

 cancriformis. — From Bronn's 

 Thierreich. 



In the anterior region are the two com- 

 pound eyes, and behind them the 

 simple unpaired eye. The whip-like 

 outgrowths of the first thoracic ap- 

 pendage project laterally. 



