An Ultrastructural Study of Spermiogenesis in Neochasmus Sp. (Cryptogonimidae: Digenea: Trematoda).

Spermiogenesis in Neochasmus sp. is shown to be representative of a pattern general for the investigated digenetic trematodes with the exception of the superficially primitive spermatozoon of Schistosoma mansoni. Thirty-two spermatids, interconnected via a cytophore, develop synchronously. Stages in spermiogenesis include: (1) development of a distal protuberance, the zone of differentiation; (2) growth of the nucleus into this zone and into the cytophore; (3) appearance in the zone of a central body flanked by two centrioles from each of which a free axoneme grows out at right angles; (4) distalwards rotation of the two flagella to fuse with an outgrowth of the zone of differentiation, the median cytoplasmic process; (5) concomitant extension of nucleus and fusing mitochondria into the median process; (6) release of the spermatid from the cytophore as the very elongate filiform spermatozoon, which has two wholly incorporated, though superficial axonemes, with loss of the centrioles and flagellar rootlets to the residual body. A spinose region of the spermatid and spermatozoon and a dense cisterna capping the median cytoplasmic process are described for the first time.