CRABS, ETC. 



95 



Order VIII. Merostomata. The king or horseshoe 

 crabs (Fig. 108) attain a length of two feet, and have a 

 wide geographical range. The last segment of the ab- 



FiG. 108. Horseshoe crab. A, Limulus Moluccanus, dorsal view. B. 

 Limulus rotundicauda, ventral view (after Milne- Ed wards) : a, ante- 

 rior ; , middle division of the body ; c, telson ; d, subf rental area ; e, 

 antennules ; f, antennae ; g, operculum ; //, breathing appendages. 



domen forms a long, sharp spine. The cephalo-thorax is 

 broad, shaped like a horse's foot ; the feet are arranged 

 about the mouth. The abdomen bears six pairs of broad 

 swimming feet, except the first having upon the under 

 side a set of about one hundred respiratory leaves or 

 plates. The young resemble the extinct trilobites, to 

 which they are allied. Some of the extinct forms, as Fig, 

 109, attained a length of nine feet. 



VALUE OF CRUSTACEANS. They are all valuable scavengers. The 

 crab, lobster, and shrimp fisheries give employment to thousands of 

 persons. The cocoanut-husks that the great Birgos tears up to line its 

 nest are used by the Malays in basket and mat making. Concretions 



