Abstract
A male Pilumnus Leach, 1816 specimen was discovered on a buoy found stranded on Chesil Beach, Chesil Cove, Portland, Weymouth, Dorset, England on 2 February 2016. The morphology of its frontal carapace margin and first gonopod suggested the crab was not P. hirtellus (Linnaeus, 1761), native to NE Europe. Closer investigation suggested the buoy originated from Florida, USA. Two morphologically similar pilumnid species are known from Florida and its environs, P. dasypodus Kingsley, 1879 and P. vinaceus A. Milne Edwards, 1880. These two species were synonymised by Rathbun (1897) due to their extremely similar morphologies. Recently, however, Magalhães et al. (2021) distinguished the two species based on genetics and subtle morphological differences. The reliability of the characters used to separate the two species is discussed, showing that they are useful but variable in form. Two other characters in the subhepatic and pterygostomial regions were found to be dependable in separating P. dasypodus from P. vinaceus. The Chesil Cove invasive is now identified as P. dasypodus s. str.
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