PHYLUM ARTHROPODA 



383 



Order 9. Xiphosura. KING-CRABS. The king-crab or 

 horseshoe crab, Limulus polyphemus (Fig. 327), occurs along the 

 Atlantic coast from Maine to Yucatan. It differs from other 

 arachnids in the presence of gills (Fig. 327, B, 11-15) an d the 

 absence of Malpighian tubules. The king-crabs and a few mites 

 are the only living marine arachnids. Limulus is a burrowing 



A B 



FIG. 327. Order XIPHOSURA. King-crab, Limulus polyphemus. A, dorsal 

 view, i, carapace ; 2, meso- and meta-soma ; 3, telson ; 4, median eye ; 

 5, lateral eye. B, ventral view. /, carapace; 2, meso- and meta-soma; 

 3, telson; 4, chelicera; 5, pedipalp; 6, 7, 8, 9, 3d to 6th appendages, walking 

 legs; 10, genital operculum turned forward to show genital aperture; //, 12, 

 13, 14, 15, appendages bearing gill books; 16, anus; 17, mouth; . 18, chilaria. 

 (From Shipley and MacBride.) 



animal and lives in the sand. It may be active at night, moving 

 by " short swimming hops, the respiratory appendages giving 

 the necessary impetus, whilst between each two short flights the 

 animal balances itself for a moment on the tip of its tail." The 

 food of Limulus consists chiefly of worms, such as Nereis (Fig. 

 163), and mollusks. These are caught while burrowing through 

 the sand, are held by the chelicerae, and chewed by the bases of 

 the walking legs. In the spring the king-crabs come near shore 

 to spawn. 



