Ultrastructural Histochemistry of Marthasterias glacialis (Echinodermata, Asteroidea) Gametes Before and After Fertilization.

The gametes of the starfish Marthasterias glacialis were studied, both before and after fertilization, using several histochemical methods at the ultrastructural level. Results showed that the oocyte jelly coat (JC) could be morphologically differentiated into a fibrillar network of acidic polysaccharides, probably containing glycosaminoglycans (GAGs), and a loose component made of neutral polysaccharides that occupies the interstices of the former. Results also suggested that it is the fibrillar component of the JC to which the spermatozoon attaches and reacts. Staining of the acrosomal vesicle contents confirmed that the peripheral dense component attaches the spermatozoon to the JC, whereas the central and apical electron-lucent component coats the acrosomal process as it extends through the oocyte investments. The acrosomal process membrane was also shown to be negatively charged. Staining of cortical vesicles confirmed their tripartite compartmentalization: the spiral lamellae fused with the fertilization envelope (FE), transferring its staining to the inner layer of the FE, whereas the matrix could be subdivided into two components--a fibrillar mesh of acidic polysaccharides that fused with the FE and some amorphous aggregates that seem to become dispersed in the perivitelline space.