Spermatozoa, spermatogenesis and fertilization in schistosoma

The spermatozoa of schistosomes are exceptional in the Digenea in having a single axoneme (two in other Digenea) which extends as a free flagellum (incorporated in others); in possessing a single diffuse central structure in the 9 + “1” axoneme (instead of the highly structured central element otherwise constant for the 9 + “1” axonemes normal in Digenea and other Trepaxonemata); in the short inverted conical (rather than filiform) condition of the nucleus and sperm body; location of more or less discrete mitochondria anterior to the nucleus (rather than filiform, fused and parallel to it); retention of a striated rootlet (rather than loss during spermiogenesis); and retention of a single centriole consisting of nine triplets (rather than two centrioles with nine doublets or singlets) (Justine 1980, 1982, 1985, 1991; Justine and Mattei 1981; Justine et al. 1993)