ULTRASTRUCTURE OF SPERM DEVELOPMENT IN THE FREE-LIVING MARINE NEMATODE ENOPLUS-ANISOSPICULUS (ENOPLIDA, ENOPLIDAE)

The development of sperm in testes of the free-living marine nematode Enoplus anisospiculus was studied with electron microscopy. The sperma togonia are undifferentiated polygonal cells with a large nucleus surr ounded by a small cytoplasm. The cytoplasm of spermatocytes is filled with numerous Golgi bodies, cisternae of the RER, ribosomes, and mitoc hondria and it forms membranous organelles (MO). The development of MO s proceeds along two parallel lines that are characteristic of two dif ferent types of spermatocyte. In the first type, MOs begin as a system of cisternae; in the second type, MOs first appear as large vesicles filled with osmiophilic material. Later in the development of spermato cytes, all MOs are bipolar because of a large eccentric dense body ass ociated with the system of cisternae. The nuclei of spermatids have a distinct nuclear envelope. During the collapse of the nucleus, mitocho ndria and MOs become closely associated with the nuclear envelope. In older spermatids, mitochondria form a layer at the future anterior end of the nucleus, all MOs are positioned posteriorly, and fibrous bodie s with a marked radial orientation appear first between the anterior l ayer of the mitochondria and the nucleus. This cluster of organelles i s retained in the immature sperm after detachment of the residual body . The distinctly external cytoplasm (ectoplasm) of the immature sperm is devoid of organelles. (C) Orstom/Elsevier, Paris.