A new species of Polydora (Polychaeta : Spionidae) from the Indo-West Pacific and first record of host hermit crab egg predation by a commensal polydorid worm

A new spionid polychaete, Polydora robi, is described from intertidal and s hallow subtidal areas in the Philippine Islands and Ball, Indonesia. Polydo ra robi belongs to the Polydora ciliata/ websteri species group and is char acterized by a rounded prostomium, triangular occipital tentacle, needlelik e posterior notosetae, and a pygidium with digitiform composite cirri surro unding the anus. Adults burrow into empty gastropod shells inhabited by her mit crabs. The burrows of the worms typically extend from an external openi ng in the apex of the shells to an opening in the central body whorls along the columella. The species was found to ingest the fertilized eggs and dev eloping embryos attached to the pleopods of host hermit crabs. The occurren ce of egg predation and the symbiotic relationship between polydorids and h ermit crabs is discussed. Known egg predators of hermit crabs are reviewed. (C) 2000 The Linnean Society of London.