Ultrastructure of sperm development in the free-living marine nematode Metachromadora itoi (Chromadoria, Desmodorida)
Yushin, V.V.; Coomans, A. (2005). Ultrastructure of sperm development in the free-living marine nematode Metachromadora itoi (Chromadoria, Desmodorida). Acta Zool. (Stockh.) 86(4): 255-265. http://dx.doi.org/10.1111/j.1463-6395.2005.00207.x
In: Acta Zoologica (Stockholm). Svenska Bokfoerlaget: Stockholm. ISSN 0001-7272; e-ISSN 1463-6395
The spermatogenesis of the free-living marine nematode Metachromadora itoi was studied with electron microscopy. Spermatocytes and early spermatids have no cytoplasmic components specific for nematodes, i.e. membranous organelles (MO) and fibrous bodies (FB). The late spermatids are subdivided into the residual body and the main cell body with a centrally located nucleus devoid of a nuclear envelope. A pair of 9 × 2 centrioles is associated with the nuclei of spermatids and spermatozoa. The nucleus of the mature spermatid is surrounded by a thick mass of radially arranged FB delimited externally by a discontinuous layer of mitochondria, which underlie a thin ectoplasm. Sperm development is accompanied by transfer of FB matter through the mitochondrion layer into the ectoplasm. The immature spermatozoa from the testis have the centrally located nucleus surrounded by a transparent halo with remnants of FB. The halo is delimited by a sphere of mitochondria that underlie the thick fibrous ectoplasm, a derivative of the FB. In the mature spermatozoa the ectoplasm is transformed into the prominent unpolarized pseudopod. The central nucleus is surrounded by a transparent halo and a sphere of mitochondria, which underlie the pseudopod. MO were not found throughout spermatogenesis. In general, spermatogenesis in M. itoi differs from that observed in many nematodes but resembles in some details the sperm development in some chromadorid and tylenchomorph nematodes. The phylogenetic importance of this sperm development is discussed.
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