Ultrastructure of spermatogenesis and sperm ofMulticotyle purvisi (Plathelminthes, Aspidogastrea)

Abstract

The ultrastructure of spermatogenesis is described for the first time in an aspidogastrean. The zone of differentiation which is usually formed during digenean spermiogenesis was not observed inMulticotyle purvisi. Instead, spermatid components are assembled within the common cytoplasmic mass before the outgrowth of spermatids. Microtubules, mitochondrion, nucleus and axonemes including their basal body regions, migrate from the cytoplasm into the spermatid which is pinched off at the level of the arching membrane. An unusual, complex structure of the basal body region is described. Intercentriolar bodies and striated rootlets are left behind and quickly disappear from the residual cytoplasm. Despite these atypical aspects, spermiogenesis results in the formation of mature sperm with the ‘classical’ structure common to Digenea and Monogenea Polyopisthocotylea with the addition of some extra, non-cortical microtubules and a dense rod along part of the length of the sperm.