First endoparasitic eulimid from Ophiuroidea and its implications for the ecological diversification of the family (Caenogastropoda: Vanikoroidea)

ABSTRACT Gastropods of the echinoderm-parasitic family Eulimidae show extraordinarily high ecological diversity. A combination of the three types of parasitism (temporary, ecto- and endoparasitism) and the five classes of extant Echinodermata allows us to identify 15 potential categories of parasitic association, all but 1 of which have already been documented. Here, we describe the last remaining category by recording the first endoparasitic eulimid in the Ophiuroidea, Introphiuricola rebeccae n. gen., n. sp., from the bursal sac of the brooding brittle star Amphiura capensis (Amphiuridae) in Cape Town, South Africa. This new eulimid is characterized by (1) a globose pyriform shell up to 1.8 mm high with a blunt apex; (2) large body whorl occupying ≥90% of the total shell height; (3) large, drop-shaped aperture with a simple prosocline outer lip; (4) brownish, dorsoventrally depressed pupiform protoconch; (5) large epipodial flap on either side of the foot; (6) endoparasitic mode of life in an ophiuroid; (7) probable protandrous sequential hermaphroditism; and (8) direct early development with no pelagic larval period. A molecular phylogenetic reconstruction reveals its close relationship to certain temporary parasites of ophiuroids with slender shells in the genera Helimiostraca, Eulima and Pyramidelloides. Its distant relationship to Stilifer, a group that also has a globose shell and lives inside asteroids, suggests an independent endoparasitic origin of the globose shape for different hosts. Benthic early development shared by the present ophiuroid and eulimid implies that this host–parasite interaction has arisen locally and remains endemic to South Africa and perhaps also Mozambique.