Sperm ultrastructure of Taenia mustelae (Cestoda, Taeniidae), an intestinal parasite of the weasel, Mustela nivalis (Carnivora)

The present paper describes the ultrastructure of spermatozoa of Taenia mus telae as revealed by transmission electron microscopy. The mature spermatoz oon of this tenid is filiform, tapered at both ends, and lacks mitochondrio n. It is capped by an apical cone of electron-dense material and presents a single helical crest-like body 75-nm thick. The axoneme is of the 9+'1' pa ttern of trepaxonematan platyhelminthes and lacks a periaxonemal sheath. Tr ansverse intracytoplasmic walls are observed in several regions of the sper matozoon. In cross-section, the spiralled nucleus shows a horse-shoe to ann ulus shape. The submembranous cortical microtubules are spiralled at an ang le of about 45 degrees to the hypothetical spermatozoon axis.