The hermit crabs of the genus Calcinus are small and colorful crustacean animals, widespread in tropical and subtropical areas. They are common on intertidal rocky shores and can be facultative associates of corals (e.g. Pocillopora, Acropora). The species of the world are revised in this work, including: 34 Indo-West Pacific species; 3 East Pacific species, 3 West Atlantic species; and 2 East Atlantic species.
The first Calcinus was described in 1836 from New Guinea (C. elegans). Forty two species are now identified, most of them described during the last 20 years from the Indo-West Pacific. This increasing number of species is a result of a better attention paid to color pattern, a character that proves to be very important within the genus and that has been largely neglected in the past, due to the lost of coloration in preservative liquids.
These small ubiquitous hermit crabs can be used as biological indicators for
reefs ecological studies and also appear to be of increasing interest for biogeographic
studies. Therefore, this electronic key intends to facilitate their determination,
a task that becomes more and more difficult as the number of species increases.