Turpeenniemi, T.A. (1998). Ultrastructure of Spermatozoa in the Nematode Halalaimus dimorphus (Nemata: Oxystominidae). Journal o f Nematology. 30 (4) :391-403.

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Turpeenniemi, T.A.

1998

30 (4) :391-403

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The ultrastructure of spermatozoa in the free-living marine nematode Halalaimus dimorphus was studied with transmission electron microscopy. Spermatozoa in the posterior testis of the male had a large cavity filled with cellular processes, which contained a variable n u m b e r o f small tubules. Mitochondria and small tubules were the only cell structures observed in the cytoplasm. The spermatozoa had a bipolar structure. The anteriorly situated nucleus, which was electron-dense and homogeneous, was surrounded by a single membrane. The size o f the small tubules in the cytoplasm (diam. 12-13 nm) and their relatively thick wall structure suggested that they were not normal microtubules (diam. 25nm). The material of the small tubules was assumed to be major sperm protein (MSP). The cavity appeared to open on the surface of the spermatozoon at the posterior extremity- of the cell, and also medially, at the level of the anterior end of the cavity. The pores apparently were closed by a special plug-like structure, which was an evagination o f the cell. The wall o f the cavity was characterized by longitudinal folds, which were mushroom-shaped in transverse section. Spermatids in the anterior testis of H. dimorphus were characterized by fibrous bodies packed with small tubules and by cellular processes also containing small tubules. H. dimorphus sperm seem to perform swimming movements based on liquid currents commonly present in turbin-like systems. Spermatogenesis resembled that found in ticks.

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