• José H. Leal

The Picky Eating Habits of Eulimid Snails

In last issue’s “Feature Story” we chatted about the eclectic food habits of the Lettered Olive, Americoliva sayana. A posting in Facebook by friend and great underwater photographer Scott Johnson prompted me to look further at the other end of the spectrum, mollusks that are very specific in their meal choices. Marine snails in the family Eulimidae are parasitic on echinoderms, i.e., sea stars, sea urchins, sand dollars, brittle stars, and others. They can be endoparasitic (living inside its host) or ectoparasitic (living outside the host, but still attached to it by its proboscis). A given eulimid species may only parasitize one or a few species in one of these main echinoderm groups. Eulimids lack the set of rasping teeth that is typical of most gastropod mollusks, the radula. They feed instead using a long, extensible proboscis to slurp the body fluids of their hosts. Scott’s image, taken last October, in Bali, shows a few individuals of an Echineulima species attached to and feeding on a Diadema sea urchin, probably Diadema savignyi. The blue iridescent lines on the sea urchin, typical of the species, probably warn nocturnal predators of the presence of the sea urchin (and its spines). (With many thanks to Scott Johnson for use of the image and to Anders Warén, Curator Emeritus at the Swedish Museum of Natural History, Stockholm, for the snail identification. Anders explained that, although species of Echineulima are not rare, it is very difficult to accurately identify them using only shell features.)