ULTRASTRUCTURE OF THE SPERMATOZOON OF THE BANK VOLE TAPEWORM, PARANOPLOCEPHALA OMPHALODES (CESTODA, CYCLOPHYLLIDEA, ANOPLACEPHALIDAE)

The mature Paranoplocephala omphalodes spermatozoon is filiform, taper ed at both ends and lacks mitochondria. Its anterior extremity exhibit s an apical cone of electron-dense material measuring about 900 nm in length and 200 nm in width, and two crested-like bodies. The cortical microtubules follow a 25-35 degrees helicoidal path along their whole length, except at the posterior extremity where they become parallel t o the spermatozoon axis. They are arranged in a single or two fields w hich may cover each other partially. The axoneme, of the 9+ ''1'' patt ern of the Trepaxonemata. lacks a peri-axonemal sheath and does not re ach the extremity of the spermatozoon. The nucleus is a compact and ir regular cord coiled in a spiral around the axoneme. Moreover, we repor t for the first time a nucleus in the spermatozoon of a Cyclophyllidea species which reaches beyond the axonemal posterior extremity. The cy toplasm, depending on the level where the section is cut, is slightly electron dense or electron lucent and contains numerous small electron -dense granules in regions III-V. In the posterior spermatozoon extrem ity, granular material is replaced by a terminal and compact electron- dense material.