The biology and systematics of polydorid worms associated with hermit crabs from shallow subtidal coral reef areas of the Philippines and Indonesia were investigated. Ten species among five genera (Boccardia, Carazziella, Dipolydora, Polydora, and Tripolydora) were identified and described utilizing light microscopy and scanning electron microscopy. The study includes the description of three new Polydora species, two of which were documented to ingest the embryos of host hermit crabs. The phylogenetic relationships of the polydorid genera were analyzed by parsimony analyses of morphological, reproductive, and ecological characters. Within the nine polydorid genera, three clades can be identified that support most previous classifications of these genera. The record of Boccardia berkeleyorum in the Philippines represents a wide range extension from the eastern Pacific (California and Vancouver Island). The species was possibly introduced by ballast water or aquacultural products and may have impacts on mariculture in the Indo-West Pacific.

The ecology of two polydorid hermit crab egg predators (Polydora robi and P. umangivora) was investigated from six provinces of the Philippines. P. umangivora constructs U-shaped burrows in the outer shell while P. robi constructs burrows in the apex of the shell, extending from a hole at the apex to an opening along the columella. Among the sites examined, P. umangivora and P. robi were found in up to 17% and 35%, respectively, of hermit crab shells collected. P. umangivora and P. robi were observed in shells of ten gastropod families, occupied by nine hermit crab species. In total, P. umangivora and P. robi preyed upon the embryos of three and seven species, respectively, of diogenid hermit crabs collected in the field. Examination of feeding behavior indicated P. robi transports the embryos to the mouth by a combination of muscular and ciliary action of the palps. In laboratory feeding experiments, P. robi ingested up to 230 developing eggs and 70 embryos of Calcinus gaimardii over a six hour period. Similarly, in field studies P. umangivora was found to ingest nearly all the embryos of Paguristes runyanae which produces smaller broods (maximum = 441). Based on the deleterious effects of egg predation on hermit crab reproduction, the nature of the polydorid/paguroid symbiosis may shift from commensalism to parasitism.

The reproduction of Polydora robi was examined from the Philippines. Females deposit broods of 18-94 egg capsules in the summer (June-August) and winter (January-March) months sampled. Egg capsules were attached by two stalks to the inside wall of the burrow and contain 40-106 eggs. The total number of eggs per brood ranged from 941 to 8761 eggs and was positively correlated with both the total number of segments and length of female worms. Development occurred within egg capsules until the 3-segment stage at which time the planktotrophic larvae were released. Juveniles of approximately 20 segments are competent to settle on gastropod shells inhabited by hermit crabs. P. robi is polytelic, producing up to nine successive broods over a three month period; a mean of 6.7 days was exhibited between broods in the laboratory. Females utilize sperm stored in the seminal receptacles during successive spawnings.