Abstract
Summary The mature S. sandoni spermatozoon exhibits an apical cone of electron-dense material about 1 μm long and a helicoidal crest-like body 50–100 nm thick. The cortical microtubules, varying in number from 0 to 18 depending on where the section is cut, are of different lengths, spiralized, and in close contact with the plasma membrane in regions III and IV of the spermatozoon where they form one or two fields of 1 to 9 units, which are associated with electron-dense subjacent material and are either laterally delimited or not by submembranous thickenings. The cytoplasm contains amorphous electron-dense material in regions II, III and IV of the gamete. The nucleus is a fine cord coiled in a spiral around the axoneme. This is of the 9+“1” pattern. Its posterior extremity is made up of only the axial element surrounded by nine singlets formed by the A microtubules attached to the plasma membrane. This type of posterior extremity of the flagellum has never been described in a platyhelminth. Similarly, submembranous thickenings and microtubular fields associated with electron-dense subjacent material have never been observed in a cestode spermatozoon. Moreover we report for the first time the existence of a spermatozoon with a single axoneme and crest-like bodies in the Proteocephalidea.
Published Version
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