THE LIFE CYCLE OF CRANGONYX RICHMONDENSIS LAURENTIANUS BOUSFIELD (CRUSTACEA: AMPHIPODA)

Abstract

Crangonyx richmondensis laurentianus Bousfield, a freshwater amphipod crustacean, occurs in small acid lakes of the Precambrian Shield where it is restricted to the shallow waters where vegetation is scarce and the sediment contains clay. Breeding occurs in late April in Little Minnow Lake, Algonquin Park. Juveniles are released from the female marsupium in mid-June and adults die soon afterwards. Immatures reach a peak of abundance in mid-July and gradually decline to a constant level in October. The summer generation does not breed until it reaches maturity the following spring. Curves of growth in length are linear during the growing season. Egg numbers increase faster than the volume of the females, and the sex ratio appears to be displaced toward the male.