GENERAL ZOOLOGY 



Fig. 15.39. Representative 

 Chelicerata. A and B, class 

 Eurypterida: restoration of a 

 generalized fossil eurypterid, 

 dorsal and ventral views. C, 

 class Arachnida: a scorpion, 

 Chaclas. D, class Pycno- 

 gonida : a sea spider, Nymphon. 

 (Redrawn from R. E. Snod- 

 grass, Textbook of Arthropod 

 Anatomy, copyright 1952 by 

 Cornell University Press, 

 printed by permission.) 



THE SUBPHYLUM CHELICERATA 



In addition to the extinct eurypterids, chelicerates include horsestioe crabs, 

 pycnogonids, and arachnids (Fig. 15.39); within this last group are placed 

 such familiar forms as spiders, scorpions, ticks, and mites. In all chelicerates 

 the body is divided into an anterior prosoma and a posterior opisthosoma; these 

 regions are comparable, but not equivalent, to the cephalothorax and ab- 

 domen of crustaceans. One of the major unifying features of chelicerates is 

 their possession of six pairs of appendages, borne on the prosoma and 

 developed in a consistent pattern. The anteriormost of these are the pincer- 

 like cheiicerae, from which the name of the group is derived. The second 

 pair, the so-called pedipalps, are variously specialized: in the horseshoe 



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