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Ultrastructure of sperm development in the free-living marine nematodes of the family Chromadoridae (Chromadorida: Chromadorina)

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Spermatogenesis in two species of free-living marine nematodes from the family Chromadoridae (Panduripharynx pacifica and Euchromadora robusta) was studied electron-microscopically. The spermatogonia of both species are undifferentiated polygonal cells with a large nucleus surrounded by a small amount of cytoplasm. In P. pacifica the cytoplasm of spermatocytes contains many Golgi bodies, cisternae of RER, ribosomes, mitochondria and dense spherical bodies. Filamentous material is accumulated in spermatids, which contain only mitochondria and a fragmented (or lobed) nucleus devoid of the nuclear envelope. The immature sperm resembles the late spermatid: its central filamentous area is surrounded by chromatine particles and occasional mitochondria. The immature sperm plasma membrane forms deep infoldings. Mature spermatozoa from the uterus consist of a small main cell body (MCB) bearing a prominent pseudopod filled with cytoskeleton filaments. The MCB contains a nucleus and mitochondria. Spermatogenesis in E. robusta (studied only in testes) resembles that described for P. pacifica, but spermatocytes of E. robusta show much lower metabolic activity and, as a result, a smaller mass of filamentous material is stored in the spermatids and immature sperm. The spermatozoa of P. pacifica and the immature sperm of E. robusta have the main ultrastructural features characteristic for nematodes (amoeboid nature, absence of axoneme, acrosome and nuclear envelope). No aberrant organelles special for many nematode sperm (membranous organelles, paracrystalline fibrous bodies and their complexes) were found during sperm development of the chromadorids studied. In this respect their spermatogenesis differs significantly from that in secernents and monhysterids.

La spermatogenèse a été étudiée en microscopie électronique à transmission chez deux espèces de nématodes libres marins (Panduripharynx pacifica et Euchromadora robusta) de la famille des Chromadoridae. Les spermatogonies, chez les deux espèces, sont des cellules indifférenciées avec un grand noyau entouré d'une petite quantité de cytoplasme. Chez P. pacifica, le cytoplasme des spermatocytes contient de nombreux corps de Golgi, des cisternae du RER, des ribosomes, des mitochondries et des corps sphériques denses. Le matériel filamenteux est accumulé dans les spermatides qui contiennent seulement des mitochondries et un noyau fragmenté (ou lobé) dépourvu d'enveloppe nucléaire. Le sperme immature resemble aux dernières spermatides: son aire centrale filamenteuse est entourée par des particules de chromatine et quelques mitochondries. La membrane plasmatique du sperme immature forme des invaginations profondes. Les spermatozoïdes matures, dans l'utérus, sont constitués par un petit corps cellulaire principal (MCB) portant un pseudopode proéminent rempli de filaments de cytosquelette. Le MCB contient un noyau et des mitochondries. La spermatogenèse chez E. robusta (étudiées seulement au niveau des testicules) ressemble à celle décrite chez P. pacifica, mais les spermatocytes d' E. robusta sont le siège d'une activité métabolique plus faible et, par conséquent, une masse plus faible de matériel filamenteux est stockée dans les spermatides et dans le sperme immature. Les spermatozoïdes de P. pacifica et le sperme immature d' E. robusta ont les mêmes caractéristiques ultrastructurales pour des nématodes (nature amiboïde, absence d'axonème, d'acrosome et d'enveloppe nucléaire) mais aucune des organelles aberrantes particuliéres à de nombreux spermes de nématodes (organelles membraneuses, corps fibreux paracrystallins et leurs complexes) n'ont été identifiées pendant le développement du sperme chez les Chromadorides étudiés. Par cet aspect, leur spermatogenèse diffère significativement de celle des Secernentes et des Monhysterides.

Affiliations: 1: Institute of Marine Biology, Far East Branch of the Russian Academy of Sciences, Vladivostok 690041, Russia; 2: Universiteit Gent, Instituut voor Dierkunde, K.L. Ledeganckstraat 35, 9000 Gent, Belgium


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