Ultraestructural study of the spermatogenesis of Anadara tuberculosa (Sowerbi 1833) (Mollusca: Pelecipoda:Arcidae)

Abstract

Anadara tuberculosa is a bivalve mollusk of the Arcidae family. This species is found at the Pacific coast, from Laguna de Ballenas (Baja California, Mexico) to Peru. Different types of germ cells have been described at the light microscopic level; however, up to date, no ultrastructural studies of these cells have been performed. The aim of the present work was to determine the main ultrastructural features of the germinal cells, and consequently to contribute on a better taxonomic characterization of different species of the Arcidae family. Spermatogonia were characterized by a large spherical and centrally localized nucleus. Heterochromatin was randomly scattered as dense granules throughout the nucleoplasm. Mitochondria were abundant, and vacuoles were seen dispersed in the cytoplasm. Primary spermatocytes had a more condensed chromatin. The number of mitochondria was lower than in spermatogonia. Secondary spermatocytes had nuclei with chromatin placed peripherically with dense granular projections to the center. Nucleus/cytoplasm ratio was lower as compared to the above mentioned cell types. Spermatids showed two stages of differentiation. At the first stage, chromatin was completely condensed with mitochondria increased in size and migrated to the basal pole of the cell. At the second stage, a centriole was seen localized between the mitochondria and acrosome. Spermatozoids showed a pyramidal acrosome and the centriole was placed intermixed with the typical five mitochondria, specific for this specie. Based in our ultrastructural data, we propose the following for this specie: 1) spermatozoids are of the primitive type 2) centriole is present up from the stage of spermatid and not at earlier stages as reported in other species and 3) five mitochondria with pyramidal acrosome are typical characteristic of this specie.