Smooth Box Crab

Calappa calappa, also known as the smooth or red-spotted box crab, is a tropical marine species of crab with an Indo-Pacific distribution, and showing great variability in its patterning and colouration. First described as Cancer calappa by Linnaeus in 1758 from a specimen originating from Ambon Island, and later in 1781 as Cancer fornicatus by Fabricius, it was finally placed in the genus Calappa by Lancelot Alexander Borradaile in 1903. The name calappa is associated with kelapa, the Malay word for 'coconut'.

Description

Occurring in the intertidal zone to a depth of 50 m, this species has a carapace of about 15 cm, indistinctly rugose on the anterior half, with wavy lines edging the posterior. It is active during the night hours, and is able, when threatened, to swiftly burrow beneath the sand. It feeds mainly on mollusks such as clams, steadying them with its legs and then, using its pincers, either prising the valves apart or breaking them.

Calappa species "have evolved structures that are specifically designed to deal with the more common dextral snails - they have essentially become right-handed. This asymmetry has evolved convergently in at least two groups of crabs, a Cretaceous crab known as Megaxantho and the extant box crabs (Calappa). Here, one of the claws is enlarged and operates with a scissor-like action that facilitates peeling open the snail."

Distribution

This species can be found in Mombasa, Seychelles, Aldabra Island, Madagascar, Mauritius, Andamans, Japan, Taiwan, Borocay, Palau, Indonesia, Papua New Guinea, Shark Bay, Abrolhos Islands, New Caledonia, Hawaiian Islands, Marquesas, Society Islands.