Ultrastructure of the spermatozoon of the proteocephalidean cestode Proteocephalus torulosus (Batsch, 1786).

The fine structure of the mature spermatozoon of the proteocephalidean tapeworm Proteocephalus torulosus, a parasite of cyprinid fishes, was studied by transmission electron microscopy for the first time. The mature spermatozoon of P. torulosus is filiform and tapered at both extremities. It contains two axonemes of the 9+"1" type and of unequal length. The anterior extremity of the spermatozoon bears a helicoidal crested body approximately 100 nm thick. Cortical microtubules of two types lie parallel to the spermatozoon axis. The nucleus is a fine cord of condensed chromatin. The slightly electron-dense cytoplasm contains electron-dense granules in regions II and III of the spermatozoon. The anterior and posterior extremities of the spermatozoon contain a single axoneme. The mature spermatozoon of P. torulosus differs from that of other Proteocephalusspecies in the presence of a single crested body and in the morphology of its posterior end.