The hairy crab, or Pilumnus hirtellus, is a tiny crab that is native to the coastal waters of western and central Europe. It lives in rocky habitats or muddy sands along ocean shorelines. Much of its body and legs are covered with bristly hairs that accumulate sediment and help the crabs hide from their predators by blending in with the background.
All types of crabs have a hard exoskeleton, or external skeleton, that covers at least some parts of their bodies. A carapace is a piece of the exoskeleton that covers the head and central portion of many crabs. The hairy crab has a fan-shaped carapace that is slightly wider than it is long. This carapace typically measures around 0.8-1.2 inches (2-3 centimeters) along its width and length and appears reddish-brown or slightly purple in color.
Hairy crabs are decapods, meaning they have ten legs. Five legs extend outward from each side of the carapace. The back four legs on either side are walking legs that help the crab scuttle along. The front two legs, one on each side, are called chelipeds, and each of them is tipped with a large chelea or pincer-like claw. The right claw is almost always noticeably bigger than the left claw in hairy crabs.
The carapace and walking legs of a hairy crab are covered with bristly hairs. In fact, hairy crabs are sometimes called bristly crabs. These hairs can accumulate silt, sediment, and muddy sand from the ocean bottom or shore, and this camouflage helps the crabs blend in with the background and hide from their predators.
The species has been found in seas around Europe, from the British Isles to northern Africa, and in the Mediterranean Sea and the Black Sea. Like most ocean-based crab species, the hairy crab lives among rocks, stones or seaweed on the ocean floor or along the coastline or in sandy holes on the beach. Although it can survive in seawater hundreds of feet (dozens of meters) deep, it mostly prefers shallower waters. It eats both vegetation and meat, including seaweed, algae, worms and the carcasses of dead sea creatures.
The Pilumnidae family, of which Pilumnus hirtellus is a member, includes dozens of other species. Many of them are also informally called hairy crabs. In addition, Chinese mitten crabs, which are members of the Varunidae family are known as Shanghai hairy crabs, or hairy crabs, for short. This species is particularly famous, because the crabs are considered a delicacy in Asian cuisine.