ULTRASTRUCTURE OF SPERMATIDS AND SPERMATOZOA IN RAMEX-CALIFORNIENSIS AND NICOLEA-ZOSTERICOLA (TEREBELLIDAE, POLYCHAETA)

The ultrastructure of the spermatozoa and some stages of spermiogenesi s in Ramex californiensis Hartman, 1944 and Nicolea zostericola (Orste d, 1844) is described. Both species brood direct developing larvae, N. zostericola outside the tube in a jelly mass, and R. californiensis i nside the tube in a cocoon. In both species, spermatids were seen in l arge groups of synchronously developing cells. Each spermatid was conn ected via a cytoplasmic bridge to a central cytophore. The acrosome in itially developed at the posterior end of the spermatid near the centr ioles. It then migrated to the anterior end of the sperm at the tip of the nucleus; in N. zostericola the migration was much later than in R . californiensis. No microtubular activity was involved in spermiogene sis. The mature sperm nuclei of R. californiensis and N. zostericola w ere basically cylindrical and elongate, measuring 9 mum and 10 mum in length, respectively. In both species the acrosome was bullet-shaped, although in N. zostericola the subacrosomal space was proportionally m uch larger, and there were two regions of differing electron density. There was no sperm midpiece in either species. Instead the mitochondri a lay in grooves along the posterior region of the nucleus; 2 mitochon dria in R. californiensis sperm and 4 mitochondria in N. zostericola. The anchoring apparatus for the sperm of each species consisted of bot h the proximal and distal centrioles, and a complex satellite apparatu s arising from the distal centriole. The morphology of the sperm is co mpared with other polychaetes; functional aspects and systematic impli cations are discussed. The close similarity of the sperm between N. zo stericola and R. californiensis does suggest a similar fertilization m echanism is used by the two species. Until a phylogenetic hypothesis f or the Terebellidae is developed the evolutionary change in sperm morp hology and functional correlates with other factors in reproduction ca nnot be determined.