Phylum Arthropoda 505 



Regeneration and Autotomy.— While crayfish do not have the 

 amazing regenerative powers of some of the lower invertebrates, they 

 are able to regenerate broken or lost appendages. At times these ap- 

 pendages are replaced by others quite unlike the original ones. This type 

 of regeneration of a different sort of appendage is known as heteromor- 

 phosis. For example, if an entire eye is removed, it is replaced by an 

 antenna-like organ. 



If a walking leg is injured, the crayfish is able to cast it off in a 

 process known as autotomy. There is a definite breaking point on each 

 of these legs where this normally occurs. There is no injury to the 

 muscle and it is accompanied by a rapid sealing off of the space through 

 which the nerves and blood vessels pass. Regeneration occurs very 

 rapidly from this stump. Autotomy has a definite protective function 

 and survival value. 



Biology. — The crayfish normally lives in a small burrow under 

 some protecting material in water. It faces outward with the large 

 chelipeds extended and the antennae moving about. Any small 

 crustacean, insect larvae, worms, snails, small fish, or even dead animal 

 material is quickly seized by the chelipeds and taken to the mouth. The 

 crayfish is most active at evening and in the morning, and they are 

 most commonly seen in spring and early summer. During the winter 

 months, they crawl into burrows for protection. Generally they crawl 

 about slowly, using their walking legs, but when frightened, they may 

 swim rapidly by using their heavy abdominal muscles. 



The crayfish are preyed upon by many different animals including 

 water birds, various aquatic mammals, turtles, water snakes, fish, etc. 

 In fact, they form an important element of the diet of many of these 

 above-named animals. 



By experimentation it has been shown that the crayfish has limited 

 powers of modifying its behavior patterns by conditioning, and thus is 

 able to do some very simple learning. 



Other Crustaceans. — Inasmuch as the members of this class are so 

 very diverse, five subclasses have been recognized. 



The first of these subclasses is the Branchiopoda whose members 

 are characterized by the possession of leaflike thoracic appendages whose 

 margins bear gills. One group of these is the fairy shrimps which live 

 in fresh water, swim on their backs, and are very abundant in the spring 

 of the year. The eggs deposited by these transparent forms are able 

 to withstand summer drying and winter freezing. While most species 



