The reproductive system of Gastrotrichs

Abstract

A structural, ultrastructural and functional analysis is made of genital organs ofMacrodasys, a member of the hermaphroditic marine Gastrotricha. The gonads are paired, hermaphroditic and polarized into male and female regions. Male and female gametes are produced simultaneously. Fertilization is internal. Accessory organs consist of, from anterior to posterior, simple male pores, a seminal receptacle and spermatheca, and, a complex caudal organ. Copulation results in reciprocal cross insemination. Sperm transfer, however, is indirect. Autosperms are transferred externally from the male pores to the caudal organ while the animals are in copula. The caudal organ then functions as a penis conducting the autosperms into the partner's seminal receptacle. This unique mode of sperm transfer is discussed with reference to the lower Bilateria and the Metazoa.