Two New Genera and Species of Polynoidae (Annelida: Polychaeta) Associated with Sea Urchins.

Symbiotic relationships between polychaetes and marine invertebrates are well-documented, with echinoderms-primary starfish and sea cucumbers-as common hosts and sea urchins being more rarely involved. Although many sea urchins possess venomous spines that are effective defenses and make them suitable hosts for symbionts, the dense packing of these spines difficult hosting symbiotic polychaetes. In this study, we describe two new genera and species of polynoid polychaetes found in association with two different species of sea urchins, collected through dredging from Sagami Bay, Japan. Echinophilia gen. nov. is characterized by an elongated body, 12 pairs of elytra, subdistally inflated antennae and dorsal cirri. Paraechinophilia gen. nov., in contrast, has a non-elongated body, 12 pairs of elytra, not inflated antennae and dorsal cirri. Additionally, we provide insights into their phylogenetic relationships based on four gene sequences (COI, 16S, 18S, and 28S).