Its flesh carries pufferfish toxins; a hard-edged mosaic pattern and black claw tips.
A heavy, smooth-shelled crab with a domed carapace to about 8 cm across, patterned in a mosaic of dark red-brown to purplish-black blotches on a cream ground, the blotches hard-edged and joined into a network rather than blurred into the background. The fingers of both claws are black. Several related xanthid crabs share the general build and something of the pattern — Atergatis floridus is plainer olive-brown, and species of Platypodia and Lophozozymus overlap in shape and markings — and since toxicity is known from a number of them, the practical approach is to treat the whole heavy-bodied, black-fingered xanthid group as one rather than to insist on a species underwater.
Lives on rubble, dead coral and the harder margins of a muck slope, under rocks by day and out in the open at night. It is slow, does not flee, and relies on the shell rather than on speed. Feeds on algae, small molluscs and detritus. Recorded from the shallows to about 20 m. The toxins are almost certainly acquired through the diet rather than manufactured by the crab, and concentrations vary widely between individuals and between localities, which is why a crab that has been eaten safely in one place has killed people in another.
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.
