Cryptic crab in Cenozoic corals

Modern coral reefs harbour a large number of cryptic species: species that are either small and/or well hidden in the nooks and crannies of the reef framework. Examples include certain fish, stomatopods, shrimps and crabs. One such group consists of members of the Cryptochiridae family or cryptic crabs. These are small, usually much less than 10mm carapace length, and fragile, because much of their exoskeleton is poorly calcified.

The phylogeny, systematics and ecology of these crabs have been an active field of research during the last few years, especially due to work of Sancia van der Meij (Naturalis Biodiversity Center, now at the Oxford University Museum of Natural History) and colleagues. The number of species known has increased notably from about about 45 in 2011 to 52 species in 2016. Along with the discovery of new taxa of these cryptic species, the placement in the Grapsoidea superfamily has been rejected and the Cryptochiridae are now firmly placed in the Cryptochiroidea superfamily.

Figure 1
Fig. 1. Modern cryptochirid crab in a crescent-shaped hole in a coral. (A and B) Troglocarcinus corallicola in the coral Manicina areolata. Scale bar equals 5.0mm for (A); and 50mm for (B). Photos by Sean Roberts.

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