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 spermatogonia are undifferentiated polygonal cells with a large nucleus surrounded by a small cytoplasm. The cytoplasm of spermatocytes is filled with numerous Golgi bodies, cisternae of the RER, ribosomes, and mitochondria and it forms membranous organelles (MO). The development of MOs proceeds along two parallel lines that are characteristic of two different 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 spermatocytes, all MOs are bipolar because of a large eccentric dense body associated with the system of cisternae. The nuclei of spermatids have a distinct nuclear envelope. During the collapse of the nucleus, mitochondria 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 bodies with a marked radial orientation appear first between the anterior layer of the mitochondria and the nucleus. This cluster of organelles is 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.