SPERMATOGENESIS AND SPERMATOZOA OF ASPIDOSIPHON-MUELLERI (SIPUNCULIDA) - AN ULTRASTRUCTURAL-STUDY

The mature spermatozoon of Aspidosiphon muelleri Diesing 1851 is of th e primitive type. It has a rounded head with a concave acrosomal nucle ar pole that is species-specific, a basal nuclear pole with an implant ation fossa, an acrosome with a postacrosomal ring, a complex pericent riolar complex with an annulus around it, 4-5 mitochondria indentating the nucleus and a long flagellum. Spermiogenesis coincides with meios is, the formation of the acrosome and the flagellum already begins in the spermatocyte. The nucleus of the Aspidosiphon muelleri spermatozoo n repeats during spermiogenesis the final developmental stage of the P hascolopsis gouldi and Golfingia ikedai spermatozoa with a convex acro somal nuclear pole. The spermatozoon of Aspidosiphon muelleri is there fore considered to be derived. During the early phases of spermatogene sis the gonad of Aspidosiphon muelleri is enveloped by peritoneal cell s with long processes extending between the spermatogonia. The periton eal cells are supporting cells which seem to have some function in the release of the spermatogonia/spermatocytes. There is no cytophore dev eloped. Granulocytes in close association with the spermatocytes float ing in the coelomic fluid seem to digest deteriorating germ cells.