South Sea flatworms hunt with poison
Off the Pacific island of Guam, marine flatworms use a neurotoxin cocktail to poison prey that is far faster and larger than themselves. The previously undiscovered worms are the first organisms to also use the well-known toxin tetrodotoxin as a hunting weapon, report scientists at the Smithsonian Naval Station.
So far, tetrodotoxin and some of its molecular derivatives have been known as a defensive weapon to deter predators in the skin of terrestrial amphibians and puffer fish - and as a communication signal, for example to attract males sexually to female fish. Raphael Ritson-Williams and his colleagues have now discovered a plathelminth temporarily referred to as "Planocerid species 1" - flattened, worm- or leech-shaped organisms that usually live on small creatures attached to the sea floor - that feeds predatory on larger molluscs as well.
Apparently he overpowers these large animals with the help of the fast-acting neurotoxin tetrodotoxin, suspect the scientists, who were able to detect the poison in high concentrations, especially in the worm's throat area. On the other hand, the poison was not effective as a defense against hungry fish, as behavioral experiments have shown: worms that were experimentally thrown to various species of predatory fish were eaten without later problems or hesitation. Cowrie shells, which were offered to hungry flatworms, were attacked by them within a short time, apparently resulting in a significant drop in the animals' toxin content. After eight days without food, however, the worms had increased their toxin levels again.
In coral reef ecosystems, fish are often considered the most important predators, the authors write - but their study shows the importance of such less conspicuous habitat inhabitants as flatworms. They, too, could hunt and kill an enormous range of animals.
