Ultrastructure of the spermatozoa and spermiogenesis in New Zealand freshwater eels (Anguillidae).

The spermiogenesis and sperm ultrastructure of Anguilla australis schmidtii and A. dieffenbachii is described. During spermiogenesis the chromatin material condenses into the crescent-shaped head of the mature sperm. By elongation of the sperm head the mitochondrion is displaced to the anterior of the head remote from the posterior centriolar apparatus. A ciliary rootlet becomes segregated during spermiogenesis to form a membrane covered, striated, rod-like appendage. From the proximal centriole arise two sets of filaments, each containing three subfibrils. One group of five filaments extends anteriorly along the inner concave side of the head. A group of four modified filaments pass along the outer, convex, side. The middle subfibril B of each triplet in the group of four filaments is flattened and joins the two subfibrils A and B, forming a binocular shaped structure. The motile flagellum has a 9+0 axonemal pattern.