Spermiogenesis and submicroscopic features of spermatozoa in Typhloplana viridata (Plathelminthes, Rhabdocoela, Typhloplaninae)

Summary

Some aspects of spermiogenesis and the submicroscopic anatomy of male gametes in Typhloplana viridata are described. In general, spermiogenesis of T. viridata follows conventional steps typical of the cytogenesis of male gametes in representatives of Plathelminthes Trepaxonemata. Spermatozoa bear two free cilia or flagella of the 2x9+“1” microtubular pattern. The filiform sperm body is characterized by the existence of dense granules linearly arranged, a single longitudinal string of mitochondria, numerous dense bodies and dense glycogen deposits. Two features are of special interest: a compartmentalization of the nucleus in meandering lamellae and a gutter-shaped structure. While most traits of mature gametes in T. viridata corroborate the hypothesis of the existence of a monophylum Rhabdocoela or of a subordinated monophylum within the Rhabdocoela encompassing distinct taxa of the “Typhloplanoida” and “Dalyellioida” (including all species of the Temnocephalida), the existence of nuclear lamellae seems to be more restricted and the gutter-shaped element may be an autapomorphic characteristic of the taxon Typhloplana (or of a monophylum that includes several genera of the Typhloplaninae) or of the species T. viridata.

Key words:

• Spermiogenesis
• spermatozoa
• ultrastructure
• Plathelminthes
• Rhabdocoela
• Typhloplana viridata
• phylogeny