Malacostracans · Decapoda · Raninidae

Spanner Crab

Ranina ranina

Not Evaluated

It has not yet been assessed against the IUCN criteria. See full glossary

An unmistakable crab, its carapace drawn out into a wedge and its legs flattened into paddles adapted for digging. It spends the day buried in the sand with only its eyes and antennae showing and hunts at night. It is a highly prized shellfish in Hawaii, Japan, Australia and the Philippines.

Size

8 cm – 15 cm

Diet

Carnivore

Feeds mainly on other animals.

Activity

Nocturnal

Active mainly at night.

Social structure

Solitary

Lives and hunts alone, joining others only to breed.

Sighting difficulty

Unknown

OceanCarnivore Nocturnal Solitary Ocean Crustacean

61countries 35parks 105dive sites

Fun facts

Unlike almost all crabs, it walks and swims forwards and backwards rather than sideways.
It buries itself backwards into the sand within seconds using its paddle-shaped hind legs.
Its shape is unique among crabs: the body is elongated and tapers towards the rear, not broad and flattened, and the abdomen remains partly extended instead of folded beneath the body.
That anatomy is an adaptation for digging: it buries itself backwards in the sand in a matter of seconds, pushing with legs transformed into shovels.
It walks and swims forwards, not sideways like almost all crabs.
It is a prized delicacy in Japan, the Philippines, Australia and Hawaii, with dedicated fisheries in several of those regions.
It hunts by ambush: buried, with its eyes poking out, it seizes fish and crustaceans passing nearby.
Its name, ranina, alludes to the resemblance of its head to a frog's.