General

The first Box Crab (Calappa calappa) was described from Ambon in 1758. Most species are night active and feed on molluscs, breaking the shells open or prising them apart with their specially adapted claws. They are one of the few crabs that are truely right-handed, an adaptation to feeding on right-handed snails!

Elbow Crabs (Parthenopidae) all hold their very long claw arms at right angles to the body, and bend them at the "elbow" so the claws meet close to the mouth parts. Little is known of their biology.

Purse Crabs earn their name from the large pouch (or "purse") at the rear of the abdomen. They are mostly night active and bury themselves quickly in the sand when threatened.

Round Crabs belong to the Xanthidae, the largest family of crabs. They are encountered in many reef niches, either free-living, hiding between the branches of corals, or half buried in soft coral. They are often brightly coloured, which serves as a warning, as they are very poisonous, producing toxins similar to those found in puffer fish livers. There is no antidote.

Some swimming crabs are commercially important. Portunus rituberculatus, accounts for a fifth of the global annual catch of crustaceans. Most species are fairly large, swim well and are aggressive hunters. Some of the larger species appear on reefs, but there is a group of small species in the genus Lissocarcinus that live in close association with sea cucumbers and soft corals. They are often overlooked and their lives are little known.