Comparative description and discussion of spermiogenesis and spermatozoal ultrastructure in some species of Heptapteridae and Pseudopimelodidae (Teleostei: Siluriformes) Quagio-Grassiotto, Irani Spadella, Maria Angélica Carvalho, Márcio de Oliveira, Claudio Neotropical Ichthyology 2005 2005-09-30 3 3 401 410 6254S 337659 Bockmann 1998 [158,322,418,441] Actinopterygii Heptapteridae Animalia Siluriformes 2 403 Chordata family    Heptapteridaespermatozoa.In the Heptapteridaespermatozoa, the head is formed by the nucleus that does not shows a nuclear fossa. The nucleus is surrounded by a narrow strip of cytoplasm with no organelles. The nucleus is occupied by highly condensed homogeneous chromatin and displays some electron-lucent areas ( Figs. 5A-B, 6A-B).  R. quelenspermatozoa have an ovoid head with an ovoid nucleus ( Fig. 5A), while in  P. gracilis,the head and the nucleus are round ( Fig. 6A). The centriolar complex remains close to the nucleus and is surrounded by a thin layer of electron-dense material ( Figs. 5A, 5E, 5F, 6A, 6E). In  R. quelen,the proximal centriole is anterior, lateral and perpendicular to the flagellum basal body - the differentiated distal centriole ( Figs. 5E-F), while in P.membranous loops at the midpiece end ( Figs. 5E, 6E). The single tail or flagellum contains the classical axoneme (9+2), and the flagellar membrane does not form lateral fins ( Figs. 5C-D, 6H).