Opal in ascidians: a curious bioaccumulation in the ovary

The role of opal deposits in the cells surrounding oocytes and cells of interstitial tissues in the ovary of the ascidian Styela clava was examined. Cytological analysis of the ovarian cells showed granular inclusions embedded in the acid mucopolysaccharides. Since the siliceous deposits were found only in the maturing ovaries, the bioaccumulation was linked to reproductive functions.