Ultrastructure of the spermatozoon of Bothriocephalus claviceps (Cestoda, Pseudophyllidea): a parasite of Anguilla anguilla (Fish, Teleostei).

The mature Bothriocephalus claviceps spermatozoon is filiform and tapered at both extremities. It contains two axonemes of unequal lengths of the 9+"1" pattern of the trepaxonemata. The anterior extremity exhibits an apical cone of an electron-dense material about 6.6 microm long by 0.2 microm wide at its base and a crest-like body making an angle of about 40 degrees with the spermatozoon axis. It is spiralized around the whole extremity of the spermatozoon. The nucleus is a cord of electron-dense material that interposes itself between the two axonemes. The cortical microtubules are of two types: hollow-centred and electron-dense centred. The cytoplasm is slightly electron dense and contains numerous electron-dense granules in regions III, IV, and V of the spermatozoon. The anterior and posterior extremities of the spermatozoon contain a single axoneme. The presence of an apical cone of the electron dense material has never, to our knowledge, been reported in the Pseudophyllidea. In addition, we show for the first time the existence of a crested body in the Bothriocephalidae.