Gymnotus aff. carapo, Linnaeus, 1758

Spermatozoa of Gymnotus aff. carapo View in CoL

- Gymnotidae

The spermatozoa of Gymnotus aff. carapo are comprised of a head ( Fig. 2A View Fig ) containing a spherical nucleus ( Fig. 2C View Fig ), a well defined midpiece ( Fig. 2 View Fig C-E) and a single flagellum ( Fig. 2 View Fig A-B-C-E). Nuclear diameter is approximately 1.9 µm. Nuclear chromatin is condensed and granular ( Fig. 2 View Fig B-C). The nucleus does not appear to undergo rotation during spermiogenesis, thus resulting in a centriolar complex and flagellum that are lateral to the nucleus ( Fig. 2 View Fig B-C). The nucleus is indented by a double, shallow, and strongly eccentric nuclear fossa ( Fig. 2B View Fig ). The proximal centriole is anterior and perpendicular to the distal centriole, both are associated with electron-dense spurs and other material, and both are located to one side of the nucleus completely outside the nuclear fossa ( Fig. 2 View Fig B-C). The midpiece contains spherical to elongate mitochondria irregularly distributed, and abundant vesicles, most of which are concentrated in the posterior portion of midpiece ( Fig. 2 View Fig C-E). Many of these vesicles are elongate and often contain electron-dense material. The midpiece also contains a short cytoplasmic canal immediately posterior to the distal centriole ( Fig. 2 View Fig B-E), but this appears to close more posteriorly. The single flagellum has a 9 + 2 microtubular axoneme which does not show intratubular differentiation ( Fig. 2D View Fig ). The flagellum lacks lateral projections or fins ( Fig. 2D View Fig ). Some irregularly arranged accessory microtubules were present in the cytoplasm of the midpiece, but these were not evident on all micrographs.