| Abstract: | Spermiogenesis and the spermatozoon were studied in Convoluta saliens, an acoel platyhelminth, by transmission electron microscopy, labelling of nuclei and immunocytochemistry of tubulin with various antibodies. Spermiogenesis involves formation of a long spermatid shaft containing two axonemes. It is established that the nucleus, after a stage of elongation, does not migrate up to the distal extremity of the spermatid, and that the centriolar derivatives are located at the distal extremity of the shaft. This contrasts with the parasitic Platyhelminthes. The mature spermatozoon, 180 μm in length, comprises a nuclear region, 50 μm in length, and a cytoplasmic region, with a short region of overlap. The cytoplasmic region contains two lateral axonemes with a 9 + 2 pattern of microtubules, granules of two different sizes, and two rows of longitudinal microtubules in the center. Each row consists of 5–6 singlet microtubules, with links between them. Whereas the two axonemes are labelled by antibodies against alpha, acetylated‐alpha, and beta tubulin, the microtubule rows are labelled only by the anti‐beta‐tubulin antibody. This suggests that acetylation does not occur in this part of the cytoskeleton, and that the epitope recognized by the anti‐alpha‐tubulin antibody (DM1A) is different in these units. Mol. Reprod. Dev. 52:74–85, 1999. © 1999 Wiley‐Liss, Inc. |
