Host use and phylogenetic position of the wentletrap Epitonium japonicum (Gastropoda: Epitoniidae)

Gastropods of the family Epitoniidae (Caenogastropoda) are ectoparasites of anthozoans but the host specificity and preference remain to be investigated for numerous taxa. In this study, the host use of the intertidal epitoniid species Epitonium japonicum was investigated by field observations and laboratory feeding experiments. The field observations were conducted at Tateyama, Chiba, central Honshu Is., Japan in 1996 and 2025. Epitonium japonicum was found parasitizing two actiniid sea anemones, Anthopleura uchidai and A. cf. inornata, with the prevalences of 4.9–18% and occupancies of 1–7 individuals. The feeding behavior of E. japonicum were tested for 12 sea anemone species of five families. Other than A. uchidai and A. cf. inornata, E. japonicum fed on three species of Anthopleura, which are distributed sympatrically with the snail. The hosts of E. japonicum may restrict to the single genus, suggesting its moderately high host specificity. In addition, sand deposit around sea anemones, where the snails were found during the field observation, might provide a cryptic, stable habitat to the snails and therefore be important for their co-occurrence. The phylogenetic position of E. japonicum was also investigated based on four-gene sequences (2,490 sites). Epitonium japonicum formed a robust clade with three congeneric species parasitizing actiniids, particularly Anthopleura spp. The host use of E. japonicum may be determined by the combination of phylogenetic constraints of the snail and host, the species composition of available sea anemones, and abiotic conditions.