Arcotheres Manning, 1993

Komai, Tomoyuki, Kawai, Kei & Ng, Peter K. L., 2020, On the identity of the poorly known pea crab, Pinnothera obesa Dana, 1852, and description of a new species of Arcotheres Manning, 1993 from the Southwest Pacific (Decapoda: Brachyura: Pinnotheridae), Zootaxa 4822 (2), pp. 221-247 : 222

Genus Arcotheres Manning, 1993

Remarks. The taxonomy of the Indo-West Pacific Pinnotheridae is still unstable, especially with regards to many of the species described in the 1800s and early 1900s. The species described in this era were often diagnosed only very briefly and key characters are omitted or not figured accurately (if at all). The identity of many species described by Bürger (1895) were partially resolved by the redescription of the extant types by Ahyong & Ng (2007) but as these authors noted, the material is often in a poor condition and host data is not always available.

For many years, the third author has been actively revising the Indo-West Pacific pinnotherids, often with S.T. Ahyong (Australian Museum) (e.g., Ahyong & Ng 2007; Ahyong 2018; Ng & Biju Kumar 2015; Ng et al. 2017; Ng 2018; Ng & Corbari 2019), and has obtained a good series of several poorly known species from Southeast Asia, notably species associated with clams of the families Arcidae and Veneridae . Most belong to the genus Arcotheres Manning, 1993 . One group of species associated with arcids is characterised by the possession of a relatively more chitinised and more calcified carapace and pereopods, as well as relatively shorter ambulatory legs. This group includes species such as A. palaensis ( Bürger, 1895) (type species of the genus) and A. arcophilus ( Bürger, 1895) . The species of a second group are associated with venerids, and include A. exiguus ( Bürger, 1895) and A. rotundatus ; those species have poorly chitinised and soft carapaces and relatively long ambulatory legs. The resolution of the identities of the Fijian Arcotheres is possible here because of many of the species in these groups have been revised and will be published in a major forthcoming study. The unpublished data from this study will nevertheless be used when required so the taxonomic problems associated with the Fijian species can be solved.