Results

Spermatozoa of Brachyhypopomus draco, Brachyhypopomus bombilla and Brachyhypopomus gauderio - Hypopomidae .

The spermatozoa of the three analyzed species are characterized by a well defined head, midpiece, and single flagellum. Both the head and nucleus tend to be spherical in B. draco (head, Fig. 1F; nucleus Fig. 1 G-H-I), but ovoid in B. gauderio (head, Fig. 1A; nucleus, Fig. 1 B-C) and B. bombilla (head, Fig. 1K; nucleus, Fig. 1 M-N). Nuclear diameter is 1.0 µm for B. draco; length and width nuclear measurements are 1.7 x 2.8 µm for B. gauderio and 0.9 x 1.8 µm for B. bombilla . Nuclear chromatin is condensed and granular in all three species, with extensive areas of lighter chromatin seen only in B. bombilla (Fig. 1 M-N).All species undergo nuclear rotation. The proximal centriole is anterior, slightly lateral and perpendicular to the distal. Electron-dense material is associated with both centrioles. The proximal centriole and most of the distal are contained within a deep nuclear fossa (Fig. 1 C-I-M). Only in B. gauderio does the fossa branch extensively throughout the nucleus (Fig. 1B). The midpiece contains several elongate mitochondria and a large number of vesicles, some of which contain stainable material (Fig. 1 B-D-G-H-M).An open cytoplasmic canal is only observed immediately posterior to the centriolar complex in B. gauderio (Fig. 1C) and B. draco (Fig. 1I) but this may close more posteriorly.An open cytoplasmic canal is not apparent in B. bombilla . An area of more organized membranous structures is only observed in the midpiece of B. draco (Fig. 1 G-J). The flagellum has the classic 9 + 2 microtubular pattern and does not show intratubular differentiation, both tubules of each peripheral doublet being electron-lucent (Fig 1 E-J-L). The flagellar membrane does not have lateral projections or fins in any of the species. However, there is substantially more cytoplasm between the axoneme and flagellar membrane in B. bombilla (Fig. 1L).