Spanner Crab

Overview

The Spanner Crab (Ranina ranina), also known as the red frog crab, is a distinctive crustacean widely distributed across tropical and subtropical waters of the Indo-Pacific. It is the only extant species in its genus and is easily recognized by its unique, elongated body shape and reddish-brown coloration.

Distribution & habitat

This species is found throughout the Indo-Pacific, ranging from the eastern coast of Africa across the Indian Ocean to Japan, Australia, Hawaii, and Vietnam. They typically inhabit coastal waters with sandy-smooth substrates, which are essential for their survival as they rely on burying themselves in the sand to hunt and hide.

Appearance

The Spanner Crab features a carapace that is noticeably wider at the front and adorned with ten white spots. Its body is covered in small, scale-like spines and hairs. It possesses strong chelipeds (claws) with seven or eight teeth and paddle-shaped walking legs, which are well-adapted for its burrowing lifestyle.

Biology & behavior

Primarily nocturnal, these crabs spend their daylight hours buried beneath the sand, often leaving only their eyes and mouthparts exposed to detect prey. They are solitary scavengers and predators that ambush small bottom-dwelling fish from their sandy hideouts.

Reproduction

Spanner crabs exhibit seasonal reproductive patterns, with peak egg-bearing activity often occurring during warmer months. Females carry their eggs attached to their bodies for several weeks before hatching. During the incubation period, females frequently remain buried in the sand to protect their developing brood.