Comparative ultrastructural study of spermiogenesis in monogeneans (flatworms): 4. Diplectanum (Monopisthocotylea diplectanidae)

Abstract

In Diplectanum sp., the common cytoplasmic mass, which contains 64 fused spermatids, is starshaped at the outset of spermiogenesis, but is globular and shows 64 parallel canals at the end. The zone of differentiation of each spermatid juts laterally into the inner enlarged part of each of these canals. The zone of differentiation contains a single centriole oriented perpendicular to its axis. After differentiation within a canal, separation of the spermatozoon occurs laterally to its anterior region. The mature spermatozoon is filiform, uniflagellate, about 20 μ m long, and shows (a) an anterior pointed centriolar adjunct; (b) a single centriole made up of nine singlets; (c) a 9 — “1”-type flagellum; (d) the distal tip of the axoneme, made up of only eight long singlets aligned along the cell membrane and associated with the filiform mitochondrion; (e) the nucleus, without any accompanying element. The spermatozoon pattern, with anterior flagellum and posterior nucleus, is inverted : it shows some resemblance to that of Acanthocephala.