Angular Crab

Overview

The Angular Crab (Goneplax rhomboides) is a distinctive, relatively small crustacean known for its rectangular, trapezoidal carapace and long, retractable eyestalks. Often called the "mud-runner" due to its ability to move quickly when threatened, this species is a common inhabitant of soft-bottom marine environments across the northeastern Atlantic and the Mediterranean.

Appearance

This crab features a smooth, strongly convex carapace that is significantly wider than it is long, typically reaching up to 4 cm in width. Each anterior corner of the carapace is marked by a conspicuous spine. The species exhibits notable sexual dimorphism: while females have relatively short claws, males possess exceptionally long, slender chelipeds that can measure up to five times the length of their carapace. The body coloration ranges from yellow and orange to reddish or vivid pink, sometimes with a violet-purple border along the carapace edges.

Distribution & habitat

Goneplax rhomboides is widely distributed from the North Sea and the British Isles south through the Mediterranean to the coasts of Africa. It prefers muddy or sandy-mud substrates, where it constructs complex, branching burrow systems. While often found in shallow sublittoral zones, it has been recorded at depths extending to several hundred meters.

Biology & behavior

These crabs are well-adapted to their soft-sediment homes, spending much of their time within their burrows. They are known to be active and capable of rapid movement when disturbed. Their antennae and mouthparts are equipped with fine bristles (setae), which assist in their daily activities.