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Keywords

Microtubules, spermatogenesis, nuclear configurations, spermatozoa, Western Siren

Abstract

I examined the ultrastructure of spermatozoa of the Western Siren, Siren nettingi, using transmission electron microscopy. My primary objective in this study was to elucidate, for the first time, the unique morphological complexity of biflagellated sperm in this species. This study also represents my fifth addition in a series of investigations that highlight the novel nature of all aspects of spermatogenesis in this salamander I show the basic sperm transverse and sagittal design which includes a nucleus, 2 axial fibers supporting 2 undulating membranes which have 2 axonemes residing at their terminal ends, several circular mitochondria, and several electron-dense masses. In addition, I illustrate that the sperm nucleus changes its morphology starting with a conical shape found anteriorly in the head region and then transitions posteriorly into multiple configurations. These configurations mostly include a dorsal flattening that may contain small diverticulae that penetrate ventrally toward the middle area of the sperm. A manchette-like, nuclear sheath of microtubules also resides attached to the dorsal and lateral surfaces of a nucleus. Moreover, an additional double layer of plasma membrane microtubules drapes the lateral and ventral regions of the sperm throughout much of its length. My findings add to a growing list of extraordinary reproductive features that set S. nettingi apart from all other vertebrates.

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