CRAYFISH, LOBSTERS, CRABS, SHRIMPS, ETC. 121 



twelve to sixteen feet across the extended legs, the body itself 

 being but little more than a foot in width or length. 



The fiddler crabs, Uca spp., so common along the Atlantic 

 coast, are the clowns among the crabs. The males have one 

 of the chelae very much enlarged, and when alarmed they 

 move this swiftly back and forth with a motion ridiculously 

 like that of a violinist with his bow. 



The blue crab, or "soft-shelled" crab, Callinectes hastatus, 

 is the most important as a source of food on the Atlantic 

 coast. On the Pacific Coast a much larger crab, Cancer 

 magister, is taken in shallow waters, sometimes in considerable 

 numbers, and is much prized. 



The horseshoe crab, or king-crab, Limulus, common all along 

 the Atlantic coast, is really not a crab at all, nor even a crus- 

 tacean, but belongs to another class, 

 the relationship which is uncertain. 

 Many believe that Limulus is most 

 nearly related to the spiders. 



The beach fleas, order Amphipoda, 

 are perhaps the most numerous crus- 

 taceans found on the sea beaches, oc- 

 curring in countless numbers in the 

 tossed up seaweeds and mosses and 

 other sea wrack. They are important 

 as food for other marine animals. The 

 boring Amphipod, genus Chelura, 



works on submerged timber, often 



, . , , r j FIG. 46. A sow-bug, 



doing a great deal of damage. isopod, species not deter- 



The wood-lice or sow-bugs, order mined. 

 Isopoda, are among the few crus- 

 taceans that live a wholly terrestrial life. They live in moist 

 places, feeding chiefly on decaying vegetable matter, but 

 sometimes attacking tender plants and doing more or less 

 damage in gardens and green-houses. Although land animals, 

 they breathe by means of gills which are situated on the under 

 side of the abdomen. It is therefore necessary for them to 

 live in places where the gills may be kept damp in order that 

 there may be a ready transfer of gases through the membranes. 



