This study describes spermatogenesis and sperm ultrastrucrure of the granular ark, Tegillarca granosa using light and electron microscopy. In the active spermatogenic season, the testis comprises many spermatogenic follicles that contain germ cells indifferent developmental stages. Primary spermatocytes in the pachytene stage are characterized by synaptonemal complexes. The early spermatids are characterized by the appearance of several Golgi bodies, increased karyoplasmic electron density, and tubular mitochondria. The mass of proacrosomal granules consists of numerous heterogeneous granules with high electron density that are about 20 run in diameter. From the midstage of spermiogenesis, the well-developed mitochondria in the cytoplasm aggregateposterior to the nucleus and surround the proximal and distal centrioles. The proacrosomal granules condense and form a single acrosome with a thin envelope. During late spermiogenesis, the acrosome begins to elongate becoming conical. The sperm is approximately 35.0 urn long and consists of a head, midpiece, and tail. The head comprises a round nucleus and a conical acrosome. A microfibrous axial rod is observed between the nucleus and acrosome. The midpiece has a calyx-like structure with five mitochondria, and the tail, which has the typical "9+2" microtubular system, originates from the distal centriole.
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