KING-CRAB 



427 



sandy shores of the sheUered bays and estuaries of North 



America, from INIaine to Florida, in the West Indies, and 



also on the Molucca Islands, etc., in the Far East. The 



body consists of a vaulted cephalothorax shaped like a 



horseshoe, and an almost hexagonal abdomen ending in a 



long spine. Burrowing in the sand, Limulus arches its 



body at the joint between 



cephalothorax and abdomen, 



and pushes forward with legs 



and spine. It may also walk 



about under water, and even 



rise a little from the bottom. 



It is a hardy animal, able to 



survive exposure on the shore, 



or even some freshening of 



the water. Its food consists 



chiefly of worms. 



The King-crab is interesting in its 

 structure and habits and also because 

 it is the only living representative 

 of an old race. 



The hard, horseshoe ■ shaped, 

 chitinous cephalothoracic shield is 

 vaulted, but the internal cavity is 

 much smaller than one would at 

 first sight suppose ; the well-defined 

 abdomen shows some hint of being 

 divisible into meso- and meta-soma ; 

 the long sharp spine is (like the 

 scorpion's sting) a post-anal telson. 

 On the concave under-surface of 

 the cephalothorax there are six (or 

 seven) pairs of limbs, as in spiders 

 and scorpions — 



(i) A little pair of three-jointed 

 chelicerae in front of and 

 bent towards the mouth. 

 (2) A pair of pedipalps lateral to the mouth. 



(3-6) Four pairs of walking legs, the bases of which surround the 



moiith, and help in mastication. Behind these, still on the 



cephalothorax, there is a pair of small appendages called 



chilaria. 



Then follows on the abdomen a double " operculum " with the 



genital apertures on its posterior surface. 



Under the operculum lie five pairs of flat plates bearing remark- 

 able respiratory organs ("gill-books"). These appendages show hints 



Fig. 239. — Limulus or King-crab. 



clr:, Chelicerse ; op., operculum ; 

 a., anus. 



