Diet relationships between parasitic gastropods Echineulima mittrei (Gastropoda: Eulimidae) and sea urchin Diadema setosum (Echinoidea: Diadematidae) hosts

Gastropods from the family Eulimidae are known as parasites of all living classes of echinoderms. Here we determine the trophic relationships between ectoparasitic eulimids Echineulima mittrei and their hosts, sea urchins Diadema setosum in Vietnam. Stable isotope analysis showed the differences in δ13C and δ15N saturation in echinoderms tissues. The eulimids’ muscle and gonad tissues have the same carbon isotopic composition as the gonads of the hosts; however, they are more saturated with heavy nitrogen isotopes. The isotopic signatures indicate that ectoparasites feed on the fatty tissues of their hosts, especially gonads. Moreover, we suggest selective feeding in eulimids and possible migration of parasites’ proboscis among different host gonads and probably changes in the metabolism of parasites.