Fish Facts

Porcelain crabs are decapod crustaceans in the family Porcellanidae, which superficially resemble true crabs. They are a good example of carcinisation, whereby a non-crab-like animal (in this case a relative of a squat lobster) evolves into an animal that only a specialist would know is not a true crab. They live in all the world's oceans, except the Arctic Ocean and the Antarctic.

Porcelain crabs are small, usually with body widths of 1-2 cm. They are common under rocks, and can often be found and observed on rocky beaches and shorelines, startled creatures scurrying away when a stone is lifted.

Porcelain crabs can be distinguished from the true crabs by the apparent number of walking legs (three instead of four pairs, the fourth pair is actually hidden under the carapace), the apparent lack of a wrist (carpal) segment on the chelipeds, and long antennae originating on the front outside of the eye stalks. Theabdomen of the porcelain crab is long and folded underneath it, free to move. In fact, when alarmed, the crab might swim by flapping its abdomen.

Porcelain crabs share the general body plan of a squat lobster (Galatheidae), but their bodies are more compact and flattened, an adaptation for living and hiding under rocks, as well as squeezing into little nooks and crannies. The porcelain crabs are quite fragile animals, and will often shed their limbs, hence their name. This trait is useful for these crustaceans because it helps them escape if a limb is grabbed by a predator or caught between rocks shifting in the current. A broken-off piece of limb may still continue to move for a short while, distracting the would-be predator as the crustacean flees. The lost appendagecan grow back over several moultings. Porcelain crabs have large chelae (claws), which are used for territorial struggles, but not for catching food.

Porcellanella triloba Procelain crab filter feeding