Paddle-legged sand crab that buries by day; males blue and white, females mottled green.
A portunid with a carapace up to about 20 cm across, the last pair of legs flattened into swimming paddles and a long sharp spine projecting from each side of the carapace. Males are blue with white mottling and carry long slender claws; females are duller, mottled green-brown, with a broader and more rounded abdomen. The genus is large and several Portunus and Thalamita have the same general build, so the working combination is paddle legs, the long lateral spine, and the male’s blue. A 2010 revision split what had long been treated as one wide-ranging species, separating Portunus armatus for Australia and P. segnis for the Red Sea and western Indian Ocean and leaving P. pelagicus for Southeast Asia and the western Pacific, so older records from outside this region may not refer to this animal.
Sand, mud and seagrass from the shallows to about 50 m. It spends the day buried with only the eyes and antennae showing and comes out at night to take bivalves, small fishes and carrion. It swims strongly with the paddle legs, which is worth seeing and is usually over quickly. It is fished hard across the whole region, which is why large males are common in markets and much less common on dived ground. Approached, it faces the diver with the claws raised rather than retreating, and holds that until pressed.
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.
