The ascoglossan (= sacoglossan) opisthobranch Mourgona germaineae Marcus secretes a viscid mucus and autotomizes cerata when mechanically disturbed. Other small invertebrates, i.e., sea anemones, amphipods, and other ascoglossans, will die when placed with these autotomized cerata or in the water in which they have been autotomized. The toxin is methanol-soluble and water-soluble and thus is probably a small molecule. Simultaneous TLC of chloroform and methanol-water extracts of M. germaineae and of its food alga, Cymopolia barbata indicates that the toxin is most likely of dietary origin.