OPAL IN ASCIDIANS - A CURIOUS BIOACCUMULATION IN THE OVARY

Densely packed granular inclusions composed of opal filaments were observed in two types of cells in the ascidian Styela clava Herdman, 1881: oocyte test cells and cells of the interstitial ovarian tissue. Cytochemical analysis, scanning electron microscopy, transmission electron microscopy and microanalysis were used to study the cytology of the ovarian cells. The inclusions consist of intracellular filaments in which silica is bound to proteins. The role of this silica accumulation, very uncommon in invertebrates, is unknown. However, the silica granules are obviously closely related to the acid mucopolysaccharides in which they are embedded. Deposition of silica is linked to the seasonal reproductive cycle, and forms in the interstitial tissue and in the maturing oocytes successively. A taxonomic significance of the silica granules is suggested.