Formation of the adult rudiment of sea urchins is influenced by thyroid hormones.

After the sea urchin embryo has developed to a pluteus larva, the adult rudiment (sea urchin rudiment) is formed, with other adult structures, on the left side of the larva and finally the juvenile sea urchin is formed after metamorphosis. We report here that thyroid hormones (THs) are involved in the formation of the adult rudiment and the adult-type skeleton and the resorption of larval tissues of the sea urchin. The contents of THs in the larval body were determined by radioimmunoassay after the separation of individual THs by HPLC. We confirmed the presence of THs in the larval body and in algae on which the larvae feed. The THs accumulate gradually following the development of the larva and reach maximum levels at the eight-armed stage when the adult rudiment is completed. These results suggest that the development of the larva is influenced by THs accumulated in the larval body. However, inhibitors for the synthesis of THs do not affect the development of the larval body, suggesting a supply of THs from algae.