Paddle-legged rubble crabs that face a light with the claws raised rather than retreating.
Portunid crabs with a carapace typically 3 to 7 cm across, broader than long, with a row of sharp teeth along each side and a set of blunt lobes across the front between the eyes. The last pair of legs is flattened into oval paddles, which places the family, and the animals swim strongly and sideways when they choose to. Colour is mottled green, brown and olive, often with blue or purple on the claws and the joints.
They are common on rubble and rock at night and are among the more conspicuous animals on a night dive, though they are rarely photographed because of what they do when found. A disturbed Thalamita backs against cover, rises on its legs and holds both claws open and forward, tracking the light. The display is a defence rather than an approach, and the crab leaves if the light does.
Species are numerous and are separated on the number and shape of the frontal lobes and carapace teeth, which is possible from a good frontal photograph and not from anything else, so records are usually left at the genus. They scavenge and take small living prey. Recorded from the shallows to about 25 m.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
