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Free keywords:
ultrastructure; spermiogenesis; spermatozoon; Schistocephalus solidus; Diphyllobothriidea
Abstract:
The spermiogenesis and the mature spermatozoon of Schistocephalus solidus
(Cestoda: Diphyllobothriidea) are described using transmission electron microscopy.
Spermiogenesis in S. solidus begins with the formation in the spermatid of
a differentiation zone surrounded by cortical microtubules and delimited by
arching membranes. This conical area presents two centrioles associated with
striated rootlets and a median cytoplasmic extension between them. The centrioles
are separated by an intercentriolar body composed of three electron-dense
plates dividing four electron-lucent plates. The centrioles give rise to two flagella
that undergo a rotation and later fuse proximodistally with the median cytoplasmic
expansion. The presence of an electron-dense material in the distal part of
the differentiation zone is observed in the early stage of spermiogenesis. This pattern
corresponds to Type I spermiogenesis according to the classification proposed
by Baˆ and Marchand (Me´moires du Muse´um National d’Histoire Naturelle
1995; 166: 87). The mature spermatozoon of S. solidus presents the Type I pattern
defined by Levron et al. (Biological Reviews 2010; 85: 523). It consists of five
regions that exhibit two axonemes, parallel cortical microtubules, nucleus and
electron-dense zones. The anterior tip of the spermatozoon possesses only a few
singlets. The axonemes are of a 9 + ’1’ trepaxonematan pattern and do not
reach the posterior extremity of the mature spermatozoon.
