External gestation of Exogone naidina Oersted, 1845 (Polychaeta, Syllidae): ventral attachment of eggs and embryos

The external gestation of sexually ripe females of the species Exogone naidina (Polychaeta, Syllidae) is described by means of SEM and TEM analysis. The eggs, embryos and juveniles are attached in close vicinity of each parapodial complex in a position immediately below each ventral cirrus and are connected to the female by a cup like structure. The formation of this adhesive disk is linked to secretory cells scattered between dermal cells of ripe female. This adhesive disk is present only in sexually mature animals and is considered as epitokous structure. The evolutive significance of ventral and dorsal attachment found within the Exogoninae is also discussed.