Pea Crabs, Pinnotheridae, are very small Crabs that often live symbiotically within the shells of Bivalves or other organisms. Members of the genus Arcotheres are often associated with Indo-Pacific Window-pane Shells of the genus Placuna, with at least three species found within the wide ranging Placuna placenta. The Singapore Window-pane Shell, Placuna ephippium, was presumed to host the same species, but such interchangeability between hosts is now considered to be rare.
In a paper published in the journal Raffles Bulletin of Zoology on 23 August 2018, Peter Ng of the Lee Kong Chian Natural History Museum at the National University of Singapore, describes a new species of Arcotheres from the Singapore Window-pane Shell, based upon examination of specimens collected around Singapore.
The new species is named Arcotheres placunicola, which appears to mean ‘Placuna-dweller’ though the derivation of this name is not given. Females of this species are subcircular and distinctly wider than long, with adults typically being a little over 10 mm in width, males are smaller, reaching only a little over 5 mm in width, and have more circular carapaces. The females are variable on colour, ranging from yellow to orange, or off-white with brown patterns, the males are greenish brown.
The new species is named Arcotheres placunicola, which appears to mean ‘Placuna-dweller’ though the derivation of this name is not given. Females of this species are subcircular and distinctly wider than long, with adults typically being a little over 10 mm in width, males are smaller, reaching only a little over 5 mm in width, and have more circular carapaces. The females are variable on colour, ranging from yellow to orange, or off-white with brown patterns, the males are greenish brown.
Two specimens of Arcotheres placunicola in situ on Placuna ephippium. Ng (2018).
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