Ovarian morphology and oogenesis in Aurelia aurita (Scyphozoa: Semaeostomae): ultrastructural evidence of heterosynthetic yolk formation in a primitive metazoan

In Aurelia aurita, the ovaries arise as horseshoe-shaped evaginations of the gastrodermis in the floor of four interradial gastric pouches. Germ-cell islands arise within endodermally-derived gastrodermal cells. Oocytes grow and gradually bulge into the mesoglea while maintaining physical contact throughout vitellogenesis with specialized cells called trophocytes. Ultrastructural changes suggest that these cells transport yolk precursors from the coelenteron to the oocytes in a manner similar to that reported for the trophonema cells of anthozoan ovaries.