Chap. 29 



ARTHROPODS CRUSTACEANS 



577 



B 



Fig. 29.6. Upper, Tidepool shrimp (Spirontocaris, length 11/2 inches). 1, an- 

 tennule; 2, antenna; 3, carapace or "saddle"; 4, abdomen; 5, tail fan; 6, swim- 

 merets; 7, walking legs; 8, pincers. Lower, Pistol shrimp, Crangon californiensis 

 (length, 2 inches) with pincers called pistol-hand closed. B shows the pistol-hand 

 "cocked." The hand is the weapon of offense and defense as these shrimps forage 

 in the tide pools where populations are dense and fiercely competitive. (Courtesy, 

 MacGinitie and MacGinitie: Natural History of Marine Animals. New York, 

 McGraw-Hill Book Co., 1949.) 



where it digs long passages that extend away from the stream, and open above 

 the ground surface through chimneys (Fig. 29.8). They are inactive in winter, 

 eat and grow very little and molt seldom if at all. During droughts, burrowing 

 crayfishes take to their tunnels, stop up the openings and retire into cisterns of 

 ground water. In early spring they appear in the open water, usually in the 

 shallows, leaving their tunnels — considerable numbers about the same time — 

 as if they had precise appointments with the softening temperature. 



A crayfish walks forward slowly with the stealth of a cat but a sudden 

 stroke of the tail fin sends it streaking backward. They capture aquatic insects 

 and fishes by lying in wait and seizing them with their claws. They notice mov- 

 ing objects but their other senses, touch, taste and smell, are more important 

 to them (Chap. 17). Frogs, turtles, and herons feed upon little crayfishes. 

 Pickerel and yellow perch take any size, tails in first, and stomachs of pickerel 

 may hold four or five packed spoonwise. The shells of one or two may be 

 completely dissolved off, while those of later arrivals have only thin spots in 

 the shells where digestion has begun. 



