THE KING-CRAB. 



359 



op. 



horseshoe, and an almost hexagonal abdomen ending in a 



long spine. Burrowing in the sand, Limnlus 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 V 



its structure and habits and also ^ 



because it is the only living repre- 

 sentative of an old race. Since 



Prof. Lankester published in iSSi 



a famous paper entitled " Limulus 



an Arachnoid/' it has been gener- 

 ally, though not unanimously, 



recognised that the King-crab's 



relationships among modern animals 



are with Arachnoidea, not with 



Crustacea. 



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 metasoma : 



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 chelicerre in front of and bent 

 towards the mouth. (They are chelate in the female, 

 simply clawed in the male.) 



(2-6) Five pairs of six-jointed walking legs, the bases of which 

 surround the mouth, and help in mastication. The last of 

 these ends in two flat plates, which help in digging. The 

 others are usually chelate, except the first in the male. 

 (7) Then follows on the abdomen a double "operculum" over- 

 lapping the rest. The genital apertures lie on its 

 posterior surface. Some refer this operculum to the 

 cephalothorax. 



FIG. 176. Li in ul i/ s or King-crab. 



di., Chelicera; ; <?/., operculum ; 

 a., anus. 



