Spermatozoon of Prosotocus confusus; all cross-sections except (a). (a) Longitudinal section of the anterior spermatozoon extremity (ASE). C, centriole. (b–e) Consecutive sections of the anterior area of the spermatozoon containing a complete submembranous layer of cortical microtubules (CM). Ax1, first axoneme; C1, centriole of the first axoneme; C2, centriole of the second axoneme. (f) Presence of two attachment zones (arrowheads). CM, cortical microtubules. (g, h) Ornamented area of the sperm cell characterized by the presence of external ornamentation of the plasma membrane (EO), spine-like bodies (SB) and the first mitochondrion (M1). (i–l) Middle area of the spermatozoon (Region II) showing one or two mitochondria. CM, cortical microtubules; G, granules of glycogen; M1, first mitochondrion; M2, second mitochondrion. (m, n) Anterior part of the nuclear region of the spermatozoon (Region III). M2, second mitochondrion; N, nucleus. Scales in μm: 0.3.