Spermatozoa of Gymnotus aff. carapo

- Gymnotidae

The spermatozoa of Gymnotus aff. carapo are comprised of a head (Fig. 2A) containing a spherical nucleus (Fig. 2C), a well defined midpiece (Fig. 2 C-E) and a single flagellum (Fig. 2 A-B-C-E). Nuclear diameter is approximately 1.9 µm. Nuclear chromatin is condensed and granular (Fig. 2 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 B-C). The nucleus is indented by a double, shallow, and strongly eccentric nuclear fossa (Fig. 2B). 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 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 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 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). The flagellum lacks lateral projections or fins (Fig. 2D). Some irregularly arranged accessory microtubules were present in the cytoplasm of the midpiece, but these were not evident on all micrographs.