Why does this crab specimen seem to be legless? It turns out to be a #Domed_Elbow_Crab (𝘊𝘳𝘺𝘱𝘵𝘰𝘱𝘰𝘥𝘪𝘢 𝘧𝘰𝘳𝘯𝘪𝘤𝘢𝘵𝘢 (Fabricius, 1787)). Crabs in the 𝘊𝘳𝘺𝘱𝘵𝘰𝘱𝘰𝘥𝘪𝘢 genus have #expanded_carapaces which completely cover the walking legs, resulting in a distinctive shape.
Although there are not many recent observation records, the Domed Elbow Crab has been recorded in Hong Kong as early as 1907, when it was then presented as “not unfrequently occurring within the harbor”.
The specimen at our museum was collected in #MirsBay in 1980. The literature shows that it is common in muddy or sandy sea bed with broken shells and a depth between 10 to 30 meters. Surprisingly, the species was not recorded on the Hong Kong page of the World Register of Marine Species (WoRMS), and the identification of our specimen was recently confirmed by Dr. Stefano Cannicci (https://www.imeco-lab.com/), who reviewed our crab collection (many thanks!)
The appearance of the Domed Elbow Crab is very different from other crabs. In addition to the #triangle_rostrum protruding from the carapace, the front edge of their carapace and the edge of the chelipeds have thin #serrations. Together with the yellowish-brown body color, all these features make them easily #camouflaged_as_a_reef to avoid predation.
If you go diving next time in mudflats or sandy shores, you can challenge yourself to find them.
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