New records of bopyrid parasites (Crustacea, Isopoda, Epicaridea) of pea crabs (Crustacea, Decapoda, Pinnotheridae) with descriptions of two new species of Rhopalione Pérez, 1921 and a review of the genus

Pea crabs (Decapoda, Pinnotheridae De Haan, 1833) are host to multiple species of ectoparasitic (Bopyridae Rafinesque, 1815) and endoparasitic (Entoniscidae Kossmann, 1881) isopods worldwide. Among bopyrids, species of Rhopalione Pérez, 1921 are unusual in residing under the pleon of their pea crab hosts. Five species of Rhopalione, all reviewed in the present report, were previously known as parasites of pinnotherid crabs, themselves symbionts of bivalve mollusks from localities worldwide. Type material of R. uromyzon Pérez, 1920 and R. incerta (Bonnier, 1900) was examined and redescribed. Specimens of R. atrinicolae Page, 1985 were obtained from the stomach of a gummy shark, Mustelus antarcticus Günther, 1870, representing perhaps the first record of a bopyrid from the gut of any species of fish. Two new species of Rhopalione, R. racemus n. sp. and R. rusa n. sp., are described from pea crabs collected in South Australia and Singapore, respectively. They mostly differ in the form of the pleopods and lateral plates of females (long and slender in R. rusa n. sp. vs short and broad in R. racemus n. sp.) and midventral tubercles of males (R. rusa n. sp. with tubercles present on pleomeres 1-4 vs R. racemus n. sp. which lacks tubercles). A key for all species of Rhopalione and a discussion of the relationships between this genus and other pseudionine genera are provided. Additionally, three new records (Dactylokepon cf. hunterae Wells & Wells, 1966, Heterocepon marginatum Shiino, 1936, and Onychocepon harpax Pérez, 1921) and notes on two species (H. globusus (Markham, 1992) n. comb. and O. giardi Nierstrasz & Brender à Brandis, 1923) of branchial bopyrid parasites of pea crabs are included. Finally, a table of all epicaridean isopods (Bopyridae and Entoniscidae) known from pea crabs is provided with discussion of their global diversity in hopes of inspiring investigations on this understudied group.