ULTRASTRUCTURAL-CHANGES IN THE STORAGE-CELLS OF THE PYLORIC CECA OF THE SEA STAR ASTERIAS-RUBENS L (ECHINODERMATA, ASTEROIDEA) DURING THE REPRODUCTIVE-CYCLE

At six week time intervals between August and June, samples were taken from the pyloric caeca of female sea stars, Asterias rubens, in order to study the ultrastructural organization of the storage cells. In Au gust, at the start of the phase of gonadal growth, the storage cells a re characterized by the presence of a large number of storage granules , an elaborate RER in the perinuclear region, and lipid droplets locat ed in the basal part of the cells. The strongly dilated cisternae of t he RER are filled with a fine granular glycoproteinous material. From October onwards, during the phase of gonadal growth, the size of the R ER gradually decreases, while the Golgi system becomes increasingly ac tive. The Golgi system produces dense-core vesicles which accumulate n ear the basal membrane, indicating that their content is transferred t o the mesenterial connective tissue layer. From December onwards the n umber of storage granules decreases and their content becomes more ele ctron-lucent, suggesting a remobilization of stored material. In April -May, just before spawning, the Golgi system is strongly reduced and r emaining elements of RER and storage granules are found in autophagic vacuoles. In June, one month after spawning, the cells again have an e laborate RER and numerous storage granules, indicating that new reserv es have been built up already. No morphological evidence has been foun d for a release of nutrients from the caeca by destruction of complete storage cells. It is concluded that the reduction of pyloric caeca we ight during the gonadal development is caused by a gradual release of substrates from storage granules, RER and lipid droplets, resulting in a decrease in cell volume.