Friday 19 October 2018

Arcotheres placunicola: A new species of Pea Crab from Singapore.

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.

Two specimens of Arcotheres placunicola in situ on Placuna ephippium. Ng (2018).

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