Carapace width to 8cm
Small, blocky, symmetrical claw arms (chelae). The other legs are broad and flat, with only the tips touching the substrate. The round, flat carapace is up to 8cm. Adults are quite variable in colour; some are muted brownish-red, some mottled or spotted brown, pink, or yellow.
This diurnal crab lives amongst rocks in the surf zone, including very turbulent conditions. Moves very rapidly in response to threats, giving rise to its common name.
Although these crabs mainly eat red and green algaethey will eat practically anything they can get including mussels, barnacles, other crabs and carrion. They use their claws to scrape food off rocks or capture live animals as well as to move the food into their mouths, and can break open tough material like mollusc and crab shells, or corals that may wash ashore.
Females carry their eggs under their bodies until they hatch, when they help to release larvae from eggs by using their chelae to disturb their egg mass and wave their bodies in shallow water.
After hatching, larvae swim out to deeper waters where they consume phytoplankton and undergo a series of quick molts. More body segments are added after each moult, and two appendages, used for swimming, are added to each new segment. Eventually larvae undergo metamorphosis, becoming juveniles. Juveniles are similar in appearance to adults but are smaller and darker, usually dark green or black with dark red limbs.
Juveniles make their way back to rocky shorelines, where they feed as adults and continue to grow by moulting, achieving greater size and brighter coloration with each molt. After this puberty molt, the chelae of males grow quickly and females' abdomens become larger in preparation to hold eggs. Adults grow throughout their lives, with longer periods of time between each molt as they age. This species can regenerate lost limbs.
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