Ultrastructure of spermiogenesis and spermatozoa of four Oriopsis species (Sabellinae, Sabellidae, Polychaeta)

The ultrastructure of sperm from four species of Oriopsis is described. Males of Oriopsis bicoloris produce sperm with an elongate nucleus divided into four rods, connected proximally, and four long mitochondria lying along the nucleus. The axoneme runs in the middle of the nuclear and mitochondria1 rods. Oriopsis brevicollaris males have sperm with an elongate nucleus and long midpiece comprised of four mitochondria wrapped around the axoneme. Males of O. mobilis have sperm with an elongate nucleus and long midpiece similar to that of O. brevicollaris , although the midpiece is much longer. Oriopsis dentata males havc sperm with a flattened head, similar to those of mammals, though the midpiece is simple and the axoneme free. The variability of reproductive mechanisms within the Polychaeta is discussed with reference to the elucidation of the function of various sperm morphologies. The implications for the taxonomy and systematics of Oriopsis , and the Sabellidae as a whole, are also discussed. It is concluded that Oriopsis is not monophyletic and examination of reproductive structures in other small sabellids is required. Study on reproduction in the type species, O. armandi , is needed to establish the reproductive method of Oriopsis and so allow revision of this genus.