THE CRAYFISH 



233 



The crayfish. Those animals having a limy exoskeleton, living 

 in the water, and breathing by means of gills are called crustaceans. 

 The crayfish is one of the best known representatives of the 

 crustaceans. The body is covered with a hard skeleton, called 

 exoskeleton, composed largely of lime. This forms an unjointed, 

 shieldlike structure, the carapace, over 

 the anterior part of the body, the ab- 

 domen being segmented and movable. 

 The coloring of the shell usually re- 

 sembles that of its natural surroundings 

 and therefore serves as a protection to 

 the animal. 



Crayfishes dart backwards through the 

 water with great rapidity, or they move 

 forward by crawling on the bottom. 

 They have five pairs of walking legs at- 

 tached to the under side of the head-thorax 

 region. These legs are jointed, and the 

 first three pairs bear pincers. The large 

 pincher claws or chelipeds (ke'li-ped) are 

 used for food-catching and for defense as 

 well as for locomotion. 



Under the abdomen, one pair on each 

 segment except the last, are found jointed 

 appendages, made up of three parts 

 called swimmer ets. The last pair, together 

 with the last segment of the abdomen, 

 form a powerful tail used in swimming. 



How the crayfish gets in touch with its 

 surroundings. Two pairs of " feelers/' the longer pair called the 

 antennae, the shorter forked pair, the antennules (little antennae), 

 are on the front of the head. The longer feelers appear to be 

 used as organs of touch and smell. The smaller antennules hold 

 at their bases little sacs called balancing organs. 



Just- above the antennules, projecting on short, movable stalks, 

 are the compound eyes. These eyes are made up of many small 

 structures each of which is a very simple eye. Such an eye 



State how the appendages are 

 used by the crayfish. 1—5 are 

 appendages found in the head 

 region; 6-13, on the thorax; 

 and M-19 on the abdomen. 



