Systematics, ecology, feeding biology, and reproduction of polydorids (Polychaeta: Spionidae) associated with hermit crabs from the Indo-West Pacific.

摘要

Polydora and related genera associated with hermit crabs from shallow subtidal coral reef areas of the Philippines and Indonesia are examined. A total of ten species among five genera (Boccardia, Carazziella, Dipolydora, Polydora, and Tripolydora) are identified and described. The study includes the description of three new Polydora species, two of which are known to ingest the embryos of host hermit crabs. A cladistic analysis of the polydorid genera based on the newly collected material, museum specimens, and literature reports supports most previous classifications of these genera. The ecology of the two polydorid hermit crab egg predators (Polydora sp. B and Polydora sp. D) is investigated from the Philippines. Polydora sp. B constructs U-shaped burrows in shells while Polydora sp. D constructs burrows in the apex of shells, extending from a hole at the tip to an opening along the columella of the upper body whorls. Among the sites examined, Polydora sp. B and Polydora sp. D are found in up to 17% and 35%, respectively, of hermit crab shells collected. In total, Polydora sp. B and Polydora sp. D preyed upon the embryos of three and seven species, respectively, of diogenid hermit crabs collected in the field. In laboratory feeding experiments, Polydora sp. D ingested up to 230 developing eggs and 70 embryos of Calcinus gaimardii over a six hour period. 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 sp. D is examined from the Philippines. Females deposit broods of 18--94 egg capsules attached by two stalks to the inside wall of the burrow and contain 40--106 eggs. The total number of eggs per brood ranges from 941 to 8761 eggs. Development occurs within egg capsules until the 3-segment stage at which time planktotrophic larvae are released. Juveniles of approximately 20 segments are competent to settle on gastropod shells inhabited by hermit crabs. Polydora sp. D is polytelic, producing up to nine successive broods over a three month period.