Spermiogenesis and sperm ultrastructure of Cotylophoron cotylophorum (Trematoda, Digenea, Paramphistomidae), a parasite of Bos taurus in Senegal.

Ultrastructure of spermiogenesis and mature spermatozoon of Cotylophoron cotylophorum are described with transmission electron microscopy. The description gives evidence of some characteristics of this digenean. The intercentriolar body situated between two striated roots and two centrioles exhibits a symmetric plane. The external bands of this intercentriolar body are formed of a line of granules. During spermiogenesis, a flagellar rotation of 90 degrees is described. The old spermatid does not present external ornamentations. The spermatozoon is characterized, in its anterior part, by the presence of a lateral expansion exhibiting a spinelike body. External ornamentations of the plasmic membrane are only present at the level of the ventral field of cortical microtubules. The posterior end of this spermatozoon exhibits a nucleus surrounded by a plasmic membrane without cortical microtubules, but exhibiting a small lateral expansion.