Over 950 hermit crabs from coral reef habitats in the Philippines were collected during 1997 and 1999 and examined for burrowing barnacles. Among these specimens, a new species of Tomlinsonia was found and is described as T. mclaughlinae n. sp. The barnacle was associated with approximately 3% of the shells inhabited by three hermit crab species of the genus Calcinus; maximally one female/male barnacle pair was found per shell. Females of T. mclaughlinae n. sp. reach lengths of over 8 mm and produce a burrow on the columella that extends toward the apex of the shell. Males are small (0.4-0.7 mm), boot-shaped, and found attached to females below the mantle aperture. The species can be differentiated from T. asymetrica of Madagascar based on proportions of terminal cirri segments, shape of the labrum, and mouthpart morphology. Among the 31 specimens of T. mclaughlinae n. sp. examined, three were parasitized by two to six males and/or juvenile females of a new species of cryptoniscoid isopod, described as Hemioniscus pagurophilus n. sp. Males of this species can be differentiated from Hemioniscus balani balani Buchholz, 1866 and H. balani japonica Ogawa & Matsuzaki, 1985 based on coxal plate dentition and shape of the ventral median lobe between the first pair of pleopods. Description of the new isopod parasite requires modification in diagnoses of Hemioniscus and Hemioniscidae; a review of the nine species of epicarideans that parasitize barnacles distributed among three families is provided. This is the first report of a species of Tomlinsonia in the northern hemisphere, of males in the genus, and the first identified cryptoniscoid isopod parasitizing acrothoracican barnacles. The feeding biology and potential for trypetesids to be egg predators of host hermit crabs is discussed.
Crustacea, Cirripedia, Tomlinsonia, Isopoda, Hemioniscus, barnacle, hermit crabs, symbionts, parasites, new species.