How do scale worms form commensal relationships with other marine animals?

Scale worms (superfamily Aphroditoidea) frequently engage in commensalism, a relationship where the worm benefits from a host without causing it harm. These worms establish these associations by inhabiting the tubes of sedentary polychaetes, the mantle cavities of mollusks (such as chitons and limpets), or by living on echinoderms like starfish and within the rectums of sea cucumbers.1

The formation of these relationships is often driven by chemical cues. For instance, the scale worm Arctonoe is specifically attracted to water flowing from its host starfish, a behavior triggered by an unidentified chemical secreted by the host. In cases where scale worms reside with tube-dwelling hosts like Chaetopterus, they benefit by consuming food particles carried in by the water currents produced by the host. These associations allow the scale worms to exploit their hosts for protection and access to resources.1