An ultrastructural study of spermatogenesis and sperm morula breakdown inArenicola marina (L.) (Annelida: Polychaeta)

Abstract

Spermatogenesis in the lugworm Arenicola marina, in common with other members of Arenicolidae, occurs in the coelomic fluid and results in the formation of discs of mature spermatozoa known as a morulae. Within a morula, individual spermatozoa are connected by a common mass of cytoplasm called the cytophore and therefore make up a syncitium. Immediately prior to spawning, and in response to an endocrine substance known as "Sperm Maturation Factor" (SMF), the structure of the sperm morulae breaks down and free spermatozoa are liberated. These are subsequently spawned from the body cavity. The investigation described here uses transmission electron microscopy to investigate the ultrastructural changes, which accompany spermatogenesis and the breakdown of sperm morulae in response to SMF in vitro. The study demonstrates that the cytophore appears to have a key role both during spermatogenesis and during sperm morula breakdown. The ultrastructure of sperm morulae and of mature spermatozoa is described. The structure of spermatozoa is shown to be primitive with a single flagellum which appears to be coiled at its distal end.

Spermatogenesis in Boccardiella hamata (Polychaeta: Spionidae) from the Sea of Japan: sperm formation mechanisms as characteristics for future taxonomic revision

“…As it has been shown in previous studies of spermatogenesis in Polychaeta (Bertout 1976; Eckelbarger 1984; Sawada 1984; Lücht and Pfannenstiel 1989; Rice and Eckelbarger 1989; Pacey and Bentley 1992), the separation of cells undergoing meiotic divisions occurs by cytokinesis that is dependent upon an actin–myosin contractile ring, according to the mechanism that is typical among metazoans (see Alberts et al. 2002).…”