In the early spermatids ( Fig. 7A) the cytoplasm symmetrically encircles the nucleus, which displays diffuse homogenous chromatin and has a circular outline. The centriolar complex lies laterally to the nucleus and is anchored to the plasma membrane. The proximal centriole is anterior and perpendicular to the distal centriole. The distal centriole differentiates into the basal body and forms the single flagellum. The nucleus rotates toward the centriolar complex ( Fig. 7B) with nuclear rotation of 90° considered complete. A depression is newly formed in the nuclear outline at the level of the centriolar complex that penetrates it ( Fig. 7C). Simultaneous to nuclear rotation, the cytoplasm projects in the direction

of the initial segment of the flagellum forming the cytoplasmic canal and midpiece

( Fig. 7A–C). The midpiece contains the mitochondria, forming vesicles and cytoplasmic canal housing the initial segment of the flagellum ( Fig. selleck chemicals llc 7B and C). In the spermatozoon of O. kneri the spherical nucleus (about 1.5 μm in diameter) contains highly condensed homogeneous chromatin interspersed by electron-lucent areas, and is surrounded by a narrow strip of cytoplasm with no organelles ( Fig. 7D Akt inhibitor and E). In the nuclear outline that faces the midpiece there is a medial and moderately deep depression, the nuclear fossa ( Fig. 7D–F). The proximal centriole, initially anterior and perpendicular to distal one, attains an oblique acute angle to the distal centriole. The centrioles are covered by electron dense material and are fastened to one another, to the

nuclear envelope at the nuclear fossa, Chloroambucil and to the plasma membrane by stabilization fibrils. The proximal centriole and most of the distal centriole are inside the nuclear fossa ( Fig. 7F and G). The midpiece contains the mitochondria, abundant vesicles and the cytoplasmic canal in which lies the initial segment of the flagellum. The midpiece is slightly asymmetric due to the unequal distribution of mitochondria and vesicles. The mitochondria are elongated and mainly accumulated in the larger portion of the midpiece. Vesicles are elongated and mainly concentrated at the periphery and at the terminal regions of the midpiece ( Fig. 7H–K). The single flagellum contains a classic axoneme (9 + 2) ( Fig. 7L). Information on spermiogenesis in A. cataphractus is not available. In P. granulosus and R. dorbignyi, as in O. kneri, spermatogenesis is cystic and spermiogenesis is Type I. In the spermatozoa of A. cataphractus, P. granulosus and R. dorbignyi the nucleus contains highly condensed homogeneous chromatin and is surrounded by a narrow strip of cytoplasm with no organelles ( Fig. 8A, E, I). The nucleus is flattened at the tip and assumes an ovoid shape in P. granulosus (about 1.2 μm in height by 1.8 μm in width) vs. almost spherical in A. cataphractus (about 1.2 μm in height by 1.3 μm in width) and in R. dorbignyi (about 1.4 μm in height by 1.3 μm in width).