CHAPTER VII 



THE JOINTED ANIMALS concluded 



THE SEA SPIDERS, KING CRABS, AND CRUSTACEANS 

 CLASSES Pantopoda, Gigantostraca, and Crustacea 



THE animals belonging to the first of the three classes named above present 

 such a marked general resemblance to the true spiders, that they have been 

 included in the same class. On the other hand, from their marine mode of life, 

 some writers have come to the conclusion that their affinities are rather with 

 the Crustaceans. As a matter of fact, it appears impossible to affiliate them with 

 either of these groups, and the general opinion is that they are entitled to form 

 a class by themselves. In all these creatures the adult is provided with four 

 pairs of well-developed legs, composed of a large and varying number of segments, 

 and each tipped with a single 

 claw. These limbs, which are 

 often exceedingly long and 

 slender, radiate from the sides of 

 the cephalothorax, which is pro- 

 duced into stalks for their sup- 

 port. In front of these limbs, and 

 attached to the headpiece, are 

 sometimes three additional pairs of 

 appendages. Hence the full com- 

 plement of limbs is seven, and not 

 six pairs as in the true spiders. 

 The first pair of appendages, 

 forming the mandibles, are short 



and often pincer-like; the second pair, or palpi, being also short; while the third 

 pair, which are only developed in the females, are shorter than the true legs, and, 

 from their function, are termed the egg-bearing legs. In some cases, however, 

 these three pairs of appendages have entirely disappeared, as in the shore spider 

 {Pycnogonum littorale). Projecting forward from the front end of the body is a 

 long rigid beak, or proboscis, at the tip of which the mouth is situated. This beak 

 is not formed by the fusion of limbs, like that of the ticks, but results from the 

 great development of the area immediately around the mouth. The cephalothorax 

 is divided into four distinct segments, of which the first, or head, supports the 

 first four pairs of appendages, and has on its summit a pair of eyes, while 

 the rest bear the three posterior pairs of limbs. Attached to the last of 

 these segments, and projecting backward between the last pair of legs, is the 

 abdomen, which is reduced to a mere tubercle or rod-like process. The greater 



(3 2I 5) 



FEMAI.E OF SLENDER SEA SPIDER, WITH EGGS. 

 (Much enlarged.) 



