Three new Indo-West Pacific species of pinnotherid crabs are described, one each of Arcotheres, Buergeres and Nepinnotheres. Arcotheres pollus, described from Paway Island, Mergui Archipelago, is most similar to A. boninensis (Stimpson, 1858), A. pernicola (Bürger, 1895) and A. purpureus (Alcock, 1900), sharing a transversely ovate carapace and long, slender, almost styliform dactyli of P4 and 5 that are about twice the length of those of P2 and 3. Buergeres choprai, described from Papua New Guinea, is most similar to B. deccanesis (Chopra, 1931) from eastern India but differentiated by segment proportions and setation of the walking legs. Buergeres tenuipes (Bürger, 1895) is synonymised with B. ortmanni (Bürger, 1895), which is also reported for the first time from Indonesia. A male of an undetermined species of Buergeres from the Philippines, possibly B. ortmanni, is figured and described, documenting the gonopod morphology in Buergeres for the first time. A key to the species of Buergeres based on females is provided. Nepinnotheres fulvia sp. nov. is also described from Papua New Guinea, and resembles N. cardii (Bürger, 1895) from the Philippines and Malaysia but can be distinguished by features of the chelipeds and maxilliped 3.
Species of the bopyrid isopod genus Rhopalione Pérez, 1920, are parasites of Indo-West Pacific pinnotherid crabs. Unlike other bopyrid parasites of brachyurans that occupy the branchial chambers, however, species of Rhopalione (subfamily Pseudioninae) infest the abdominal cavity. Prior to the present study, four species of Rhopalione were recognized: R. atrinicolae Page, 1985 (New Zealand), R. incerta (Bonnier, 1900) (Madagascar), R. sinensis Markham, 1990 (East Asia), and R. uromyzon Pérez, 1920 (Persian Gulf). A fifth species of Rhopalione, from Perhentian Besar, Malaysia, is described herein, parasitic on the pinnotherid crab Serenotheres besutensis (Serène, 1967). Keys are provided to females and males of the species in the genus.