SEX-DIFFERENTIATION IN THE CRAB ERIOCHEIR JAPONICUS (DECAPODA, GRAPSIDAE)

The sex differentiation of the crab Eriocheir japonicus was studied hi stologically and morphologically from the first zoeal stage to the fif th crab stage. The gonoducts were the first sexual characteristic that underwent sex differentiation. As early as the crab was at the megalo pa stage, gender could be determined on the basis of two different ori entations of the gonoducts. One orientation was toward the eight thora cic sternite in the males and the other was toward the sixth thoracic sternite in the females. The second sexual characteristic that underwe nt sex differentiation was found in the pleopods at the third crab sta ge. No remarkable morphological or structural difference was observed between the gonia in males and those in females. We compared our findi ngs with those in the crabs studied in previous research regarding the sequences of the sex differentiation of sexual characteristics and th e development of gonoducts and gonopores. We also discussed the timing of the appearance of the androgenic gland in the sex differentiation of decapods and other malacostracans. Unlike isopods and amphipods, no androgenic gland is visible prior to sex differentiation in E. japoni cus. This finding is consistent with those reported in other decapods. We hypothesize that in decapods, before the androgenic gland cells fo rm a gland, they already exist dispersively in both sexually undiffere ntiated genetic males and females. In the genetic males, these dispers ive androgenic gland cells may be activated by the male sex-determinin g genes to produce androgenic gland hormones inducing sex differentiat ion.