What is the Crab Sesarmops impressus?

One of the most easily recognised crabs in fast-flowing streams and lowland waterfalls in Southeast Asia is the large crab currently known under the scientific name of Sesarmops impressus. With its large size (body up to 40 mm in width) and powerful purple claws, it is easily recognised and has been been widely reported throughout the Indian and Pacific Oceans. Appearances are deceptive. As it turns out, the present revision by Taiwanese scientists and their colleague show that there are actually three species “hiding” under this one name! The real Sesarmops impressus is known only from Madagascar and the eastern Indian Ocean and actually prefers mangrove habitats and has a very different colour pattern in life! Then there is another hidden new species living in the islands of the western Ocean, S. indicus, which has longer legs and a different reproductive structure! Most surprising of all, the common species living in Southeast and East Asia is also a new species, which the study here names S. imperator. The Emperor Waterfall Crab is so named in reference to its purple claws (purple is the colour reserved for royalty in ancient Europe)! The identities of two other large species living in Fiji and Samoa described in 1865, previously confused with S. impressus, are also clarified.

Read the full article, published by Zoological Studies, here

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