Search

Summary Gametogenesis in the Chinese pen-shell bivalve, Atrina maura (Sowerby, 1835) was provoked under artificial conditions in a running water system maintained under constant environmental conditions in semi-closed tanks. The specimens were fed with a diet commonly used in experimental hatcheries. Gametogenesis was described using stereological techniques (based on the oocyte diameters), classical and semi-thin histology procedures, and electron microscopy. Four reproductive stages were recognized based on oocyte size and cytological characteristics of the gonad: early gametogenesis (4–15 μm), growing (16–30 μm), mature (31–45 μm), and degenerating (46–65 μm). During gametogenesis, the auxiliary cells surrounded the oocyte basal region in the growing stage, afterward disappearing. A process of auto- and heterosynthesis characterize the mature stage, and nuclear deterioration and cytoplasmic membrane disintegration define the degenerating stage. The ultrastructural study of gonads showed that the cytolo...

Summary Bathypecten vulcani is considered a relict species from the Paleozoic, based on shell characteristics such as the presence of calcite prisms. To date, it is the only pectinid species reported from hydrothermal ecosystems. Histological and ultrastructural studies show that spermatogenesis is identical to that of littoral pectinids. The spermatozoon has a 2.7 μm long pyriform head and a 40 μm flagellum. The four mitochondria of the mid-piece are about 1.2 μm in diameter. The nucleus contains dense chromatin fibres and possesses a wide, shallow (0.1 μm) anterior fossa and a narrow, deeper (0.2 μm) posterior nuclear fossa. Comparison of the ultrastructural characteristics of the spermatozoon of B. vulcani with those of littoral pectinids shows that they can be used as a diagnostic feature of this species. In particular, its acrosome characters will be a useful complement to the shell characters in the study of the phylogenetic position of this species in relation to other pectinids.