The absence of morphological external characteristics that allow the recognition of the sex as well as the presence of both male and female gonopores in the same animal [except in some sexual forms of Parastacus nicoleti (Philippi, 1882)] gives rise to the hypothetical existence of some form of hermaphroditism in crayfishes belonging to the genus Parastacus Huxley, 1879. Specimens of Parastacus brasiliensis (von Martens, 1869) were collected in a rivulet at Mariana Pimentel municipality, Rio Grande do Sul, Brazil. In the laboratory they were reared and dissected. The results suggest that P. brasiliensis may be a sequential hermaphroditic species, but male and female gonadal tissues were not simultaneously present in the analized samples. In testes and ovaries two pairs of genital ducts are present; that connect, respectively, to the gonopores on the coxae of the fifth and the third pairs of pereiopods. In the females only the apertures and anterior ducts seem to be functional, while in the males only the apertures and posterior ducts may be functional. The existence of different degrees of obstruction in the female genital apertures and different degrees of projection in the male genital apertures was observed. The aspect of the gonopores were used to recognize, externally, the sex of animais.
Parastacidae; Paraslacus; brazilian crayfish; reproductive system; hermaphroditism