Abstract
The ultrastructure of the male gonad of Eulimnadia texana (Branchiopoda, Spinicaudata) has been observed for the first time to investigate the sexuality of a well studied case of androdioecy in animals. The male gonad is a double structure located in the hemocoel throughout the entire body length on each side of the midgut. Male gametes originate from the wall and mature centripetally towards the lumen; the proliferative activity is very high and continuous and therefore the mature gonad is full of numerous germ cells. Inside the lumen several degenerative stages are found mixed with sperm cells and spermatids, the latter two being not easily distinguishable because of the slight differences between them. The evolutionary meaning of the degenerative process in E. texana male gametes is difficult to explain, and we propose some hypotheses about its possible role or cause in the studied population: a) to help build spermatophores, b) to act as a trophic component for viable sperm, c) a manifestation of inbreeding depression and/or d) to regulate the number of sperm cells.