COMPARATIVE SPERMATOLOGY OF THREE SPECIES OF DONAX (BIVALVIA) FROM SOUTH AFRICA

Abstract

The fine structure of the sperm and spermatogenesis in three species of Donax (D. madagascariensis, D. sordidus and D. serra) are described. Although the morphology of the sperm of all species is very similar, each has unique features. Donax madagascariensis and D. sordidus reportedly hybridize in regions of sympatry and their spermatozoa are morphologically closer to one another than to D. serra. All sperm are of the primitive type with ahead (about 2 μmu; long), mid-piece of four mitochondria and tail. The head comprises a barrel-shaped nucleus which is capped by a small, complex acrosome. The structure of the acrosome is typical of heterodont bivalves. During spermatogenesis the pattern of nuclear chromatin condensation is granular. Glycogen first appears in the cytoplasm of spermatids, and in the mature sperm is sited in the mid-piece and base of the acrosome.