The fine structure of the yolk nucleus in oocytes of Antedon bifida (Pennant) (Echinodermata: Crinoidea)

Abstract

The yolk nucleus of Antedon bifida is a large, intensely basophilic structure located in the cytoplasm of small to medium-sized oocytes. Electron microscopy reveals that this yolk nucleus is a conglomeration of hundreds of dense clumps. Each clump, which is a micrometer or two in diameter, consists of finely fibrogranular material in which are embedded ribosome-like particles. Also present in the oocyte cytoplasm are perinuclear dense granules, which may well be the precursors of the clumps making up the yolk nucleus. The yolk nucleus does not appear to participate directly in the elaboration of the yolk granules.