Polydora and Related Genera Associated with Hennit Crabs from the Indo-West Pacific (Polychaeta: Spionidae), with Descriptions ofTwo New Species and a Second Polydorid Egg Predator of Hennit Crabs1

Polydora and related genera associated with hermit crabs from shallow subtidal coral reef areas of the Indo-West Pacific are described. Over 2000 hermit crabs were collected from localities in the Philippines and Indonesia between July 1997 and April 1999. In total, 10 species of polychaetes among five genera (Boccardia, Carazziella, Dipolydora, Polydora, and Tripolydora) were identified and described. Adult morphology of these species was investigated with light microscopy and scanning electron microscopy. The study includes the description of two new Polydora species, including the second known polydorid egg predator of hermit crabs. Six of the species burrow into calcareous substrata, living in burrows within live or dead gastropod shells or coralline algae attached to shells. Two species were found in mud tubes within crevices of gastropod shells inhabited by hermit crabs. The zoogeography and biodiversity of polydorids from the West Pacific are discussed. The diversity of polydorids from the Philippines is comparable with that of other central Pacific and Indo-West Pacific islands, but it is lower than that in areas of the North and Southwest Pacific; lower diversity probably reflects disparity in sampling efforts between these regions. A key to the Philippine polydorids is provided. POLYCHAETES ARE COMMON associates of hermit crabs, either living on, within, or burrowing into occupied gastropod shells (e.g., Jensen and Bender 1973, Stachowitsch 1980, Hoberg et a1. 1982, Karlson and Shenk 1983, Walker 1995). In particular, Polydora and related genera (termed polydorids, nine genera of the family Spionidae that contain a modified fifth segment) are known to burrow into calcareous substrata including gastropod shells occupied by hermit crabs (Blake and Evans 1973, Read 1975, Radashevsky 1993, 1 This work was supported by the Lerner-Gray Fund for Marine Research (American Museum of Natural History), a Libbie Hyman Memorial Scholarship (Society for Integrative and Comparative Biology), and a Graduate Fellowship from the University of Rhode Island. Manuscript accepted 3 February 2001. 2 Department of Biological Sciences, 100 Flagg Road, University of Rhode Island, Kingston, Rhode Island 02881-0816. Current address: Department of Biology, Hofstra University, Hempstead, New York 11549-1140. Pacific Science, vol. 55, no. 4:429-465 © 2001 by University of Hawai'i Press All rights reserved Blake 1996, Martin and Britayev 1998, Williams 2000). The burrowing behavior of these species has been investigated in substantial detail because of their effects on commercially important mollusk species (see Radashevsky and Williams 1998). Polydorids have been considered to be facultative or obligate commensals of hermit crabs, but recent research indicates that the worms can have negative effects on their hosts (Buckley and Ebersole 1994, Williams 2000). The purpose of this investigation was to examine the systematics and ecology of polydorids associated with hermit crabs from coral reef areas of the Indo-West Pacific. The Spionidae is one of the most conspicuous polychaete families of Indo-West Pacific islands, in many areas second only to the family Syllidae in number of recorded genera (Knox 1957, Bailey-Brock 1995, Paxton and Chou 2000). Polydorids are common inhabitants of coral reef areas, and some species are bioeroders found to burrow in live and dead corals and mollusk shells (Hartman 1954, Bailey-Brock 1995). In spite of the amount of work completed in the North and