Stages in the development of the embryo of the fresh-water crayfishCherax destructor.

Development of the crayfish embryo is described in sequential stages separated by intervals that represent 5% of the total time taken from fertilization to hatching, which is 40 days at 19° C. Early cell division, aggregation of blastoderm cells into the ventral plate, gastrulation and formation of the embryo can be clearly observed through the transparent chorion and each stage characterised using morphological criteria. At hatching the egg chorion splits open but the hatchling (postembryo stage 1) remains attached to the inside of the egg by membranes extending from its tail. 7 to 8 days later the hatchling moults to produce the 2nd post-embryonic stage. Free from the egg, it still clings to the mother. 14 days later the 2nd postembryonic stage moults to produce the immature adult.