ULTRASTRUCTURE OF OOGENESIS IN PENAEUS-KERATHURUS (CRUSTACEA, DECAPODA) - I - PREVITELLOGENIC OOCYTES

Although Malacostracan species represent an important alimentary human resource, the ultra-structure of oogenesis in P. kerathurus remains u nknown. Previtellogenic oocytes of Penaeus kerathurus possess a large nucleus with several peripheral nucleoli. The endoplasmic reticulum (E R) is originated from expansions of the nuclear envelope (NE) and cont ains small dense granules, which are first formed inside the intermemb ranous space of the NE but are later exported to the ER lumen. Direct vesiculation from the NE and ER then give rise to the Golgi complexes. Small yolk vesicles appear to be mainly formed by vesiculation of the ER, but also receive materials from the Golgi complexes. They contain a fine fibrillar content which seems to originate from decondensation of the small dense granules. Small vesicles and small multivesicular bodies originated from the NE, ER and Golgi complexes, as also myelin figures directly shedded from the NE, fuse together to give origin to large multivesicular bodies (MVB). These organelles, which have an inc omplete membrane and appear meshed within nuage materials, give origin , at a later stage, to lipid droplets that are thereafter extruded int o the cytoplasm. Neighbouring oocytes exhibit intercellular bridges, t he remaining of their surface being surrounded by a single layer of fl attened follicular cells. These results show for the first time in Mal acostraca the existence of oocyte intercellular bridges, that the ER a nd Golgi complexes arise from NE activity, that early yolk formation i s endogenous and derives from the activity of the NE, ER and Golgi com plexes, and that lipid droplets are products of intracellular membrane recycling activity occurring within large multivesicular bodies.