LIFE CYCLE
The Shape of the Crayfish
The head and thorax of a Crayfish are covered by a shell-like carapace, and anterior point of this, the rostrum which projects between the eyes, is the key feature for easy Crayfish identification. The most noticed feature of Crayfish morphology is the chelipeds or anterior pereopods and their chelae, pincers, or claws.
There are four more pairs of walking pereopods attached to the thorax behind the chelipeds. The jointed abdomen, which can be folded under the thorax, has 5 pairs of small appendages called pleopods, or swimmerets. The first two pleopods of males are modified as copulatory stylets, also called gonopods. In female crayfish the first two pleopods look the same as all the rest. The pleopods beat to maintain a current of water over the feather-like gills which extend up from the bases of the walking legs under the carapace.
At the end of the abdomen is the telson, which together with the paddle-shaped uropods forms a flipper-like tail. A crayfish normally walks forward on its pereopods, but when frightened it flips its tail rapidly and repeatedly under its thorax and scoots away backwards.
The Life of the Crayfish
As Arthropods, Crayfish shed their exoskeleton skins as they grow. For several days after moulting, the soft-shelled crayfish stay hidden until the new exoskeleton hardens. Mature males assume a Form I morphology with large claws, bright colour and exaggerated ornamentation. Form I males are capable of mating, and after the species' mating season surviving males moult into the Form II condition which is more similar to that of the female. A Form I male mates by grasping a female with his claws and transferring sperm to the female sperm receptacle. Females lay the eggs onto their swimmerets in a mass with the overall texture of a raspberry, so that females are said to be "in berry" while they are carrying their eggs. The hatchlings cling to the swimmerets for a while and then become free-living. They look just like miniature adults, and grow to half of adult size in their first year.
Some Crayfish live permanently in streams and lakes, while others burrow in soil, living for most of the year in deep burrows topped with chimneys of mud balls. Cambarus species are active almost exclusively at night, while Orconectes are more often seen out from under cover during the day. At night one sometimes sees Crayfish up on land, foraging or travelling between pools of water.
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