Abstract
The nudibranch,Glossodoris quadricolor (Doridacea) feeds on the red spongeLatrunculia magnifica, which grows in the reefs of the Gulf of Aqaba, Red Sea. The ichthyotoxic substance from the sponge, latrunculin B, was also indentified in the mucous secretion of the mollusk by TLC, indicating the use of this substance as defense allomone.