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Sperm Structure (sperm + structure)
Selected AbstractsSperm structure of Rhopalura littoralis (Orthonectida)INVERTEBRATE BIOLOGY, Issue 2 2002George S. Slyusarev Abstract. We present here a description of the spermatozoon of Rhopalura littoralis, the first fine-structural study of an orthonectid sperm. The spermatozoon contains a slightly elongate nucleus and two centrioles orientated along the longitudinal axis of the sperm. The proximal centriole bears one rootlet. A single mitochondrion is present in the mid-piece region. An acrosome is absent. The sperm tail is a simple flagellum with 9+2 structure. We consider the orthonectan spermatozoon to be closer in structure to those of Porifera, Cnidaria, and Annelida, than to Aschelminthes and Platyhelminthes, to which orthonectids have previously been allied. [source] Ultrastructure of Gnathostomaria lutheri Ax (Gnathostomulida: Scleroperalia).I.MARINE ECOLOGY, Issue 1-2 2001An Hypothesis About the Origin of Micropodia in Scleroperalian Sperm Abstract. Initially described as an aberrant taxon of turbellarian flatworms, the Gnathostomulida were recognized as a distinct phylum by Rupert Riedl already in 1969. Yet these microscopic, non-segmented marine worms remain organisms of enigmatic phylogenetic affiliation, and although they are often the dominant invertebrate taxon in detritus-rich, oxygen-poor sands, our knowledge of their biology is still very scanty. About 90 gnathostomulid species are known to date; they are grouped in two orders, one with two suborders. Sperm structure, often a useful instrument for clarifying evolutionary pathways in metazoan taxa, differs so widely between the orders and suborders that sperm phylogeny within the Gnathostomulida also remains uncertain. We here report on the ultrastructural features of a peculiar type of sperm, the aflagellar "megasperm" of Gnathostomaria lutheri, and discuss new and older interpretations of sperm cytology of the taxon. [source] Spermatogenesis in Boccardiella hamata (Polychaeta: Spionidae) from the Sea of Japan: sperm formation mechanisms as characteristics for future taxonomic revisionACTA ZOOLOGICA, Issue 4 2010Arkadiy A. Reunov Abstract Reunov, A.A., Yurchenko, O.V., Alexandrova, Y.N. and Radashevsky, V.I. 2009. Spermatogenesis in Boccardiella hamata (Polychaeta: Spionidae) from the Sea of Japan: sperm formation mechanisms as characteristics for future taxonomic revision. ,Acta Zoologica (Stockholm) 91: 477,456. To characterize novel features that will be useful in the discussion and validation of the spionid polychaete Boccardiella hamata from the Sea of Japan, the successive stages of spermatogenesis were described and illustrated. Spermatogonia, spermatocytes and early spermatids are aflagellar cells that develop synchronously in clusters united by a cytophore. At the middle spermatid stage, the clusters undergo disintegration and spermatids produce flagella and float separately in coelomic fluid as they transform into sperm. Spermatozoa are filiform. The ring-shaped storage platelets are located along the anterior nuclear area. The nucleus is cupped by a conical acrosome. A nuclear plate is present between the acrosome and nucleus. The nucleus is a cylinder with the implantation fossa throughout its length and with the anterior part of the flagellum inside the fossa. There is only one centriole, serving as a basal body of the flagellum, situated in close vicinity of the acrosomal area. A collar of four mitochondria is located under the nuclear base. The ultrastructure of B. hamata spermatozoa from the Sea of Japan appears to be close to that of B. hamata from Florida described by Rice (Microscopic Anatomy of Invertebrates, Wiley-Liss, Inc., New York, 1992), suggesting species identity of the samples from the two regions. However, more detailed study of Florida's B. hamata sperm is required for a reliable conclusion concerning the similarity of these two polychaetes. In addition to sperm structure, features such as the cytophore-assigned pattern of spermatogenic cell development, the synchronous pattern of cell divisions, the non-flagellate early spermatogenic stages, and the vesicle amalgamation that drives meiotic cell cytokinesis and spermatid diorthosis will likely be useful in future testing of the validity of B. hamata and sibling species throughout the world. [source] Sperm morphology of the eurasian beaver, Castor fiber: An example of a species of rodent with highly derived and pleiomorphic sperm populationsJOURNAL OF MORPHOLOGY, Issue 8 2007Joanna B. Bierla Abstract The structural organization of the spermatozoon from the Eurasian beaver, Castor fiber (Family: Castoridae), was determined and compared to that of other sciuromorph rodents. The beaver spermatozoon has a head, which is variable in form but usually paddle-shaped, with a small nucleus and very large acrosome, and a tail that is relatively short compared to that of most other rodents. Transmission electron microscopy indicates that in most testicular spermatozoa the acrosome projects apically, although in a few it becomes partly flexed. During the final stages of maturation, however, the acrosome becomes highly folded so that the apical segment comes to lie alongside part of the acrosome that occurs lateral to the nucleus, with, in some cases, fusion taking place between the outer acrosomal membranes. The sperm nucleus is wedge-shaped, being broader basally and narrowing apically with an occasional large nuclear vacuole occurring. This spermatozoon structure is markedly different from that found in the other species of Geomyoidea, which is the sister group of the Castoridae. The findings thus emphasize the highly divergent nature of the beaver spermatozoon and demonstrate that, within the proposed Infraorder Castorimorpha, very large differences in sperm structure have evolved. J. Morphol., 2007. © 2007 Wiley-Liss, Inc. [source] | ||||||||||