Ultrastructure of the spermatozoon of Holorchis micracanthum (Digenea: Lepocreadiidae), an intestinal parasite of Plectorhinchus mediterraneus (Pisces, Teleostei) in Senegal.

The mature Holorchis micracanthum spermatozoon exhibits an apical cone of electron-dense material forming a lateral extension, extramembranar ornamentations, and two fields of cortical microtubules, delimited by attachment zones. The axonemes, of the 9 + "1" pattern of the Platyhelminthes, are shifted longitudinally, one compared to the other. The nucleus, with a fibrous chromatin and a more or less circular section, granules of electron-dense material, and a moniliform mitochondrion are present. The latter, in longitudinal sections, appears in the form of successive bulges, connected to each other by a fine mitochondrial cord, and extends along almost the whole length of the gamete. To our knowledge, a moniliform mitochondrion has never been described before in a digenean. Likewise, the presence of a lateral extension of an apical cone of electron-dense material has never been previously reported in the Lepocreadioidea. In addition, in this work, we show for the first time the existence of extramembranar ornamentations in a species of the Lepocreadiidae.