CrabsBrachyura

Crabs (Brachyura) are crustaceans distinguished by a broad, flattened cephalothorax encased in a hard carapace, and a small abdomen tucked tightly beneath the body. All members possess ten legs, with the front pair typically forming strong pincers (chelae) used for defense, feeding, and courtship. Carapace width varies significantly among species, from less than 1 cm (0.4 in) in the smallest forms to over 20 cm (8 in) for larger species found on 🌊 Red Sea reefs. Many species display cryptic coloration, with carapaces patterned in shades of brown, grey, green, red, or orange to blend with their surroundings.

Crabs inhabit diverse marine environments, including intertidal zones, sandy flats, coral reefs, and rubble fields, living from the surface down to at least 100 m (330 ft) depth. Primarily scavengers, they consume algae, detritus, and carrion, though many also actively hunt molluscs, worms, and small fish, using smaller mouthparts to shred food before ingestion. Most species walk swiftly, either sideways or forwards; however, some families, such as swimming crabs, feature flattened hind legs adapted for propulsion through water. A notable trait is their ability to regenerate lost limbs through autotomy during molting. Divers frequently encounter crabs hidden in reef crevices, under rocks, or camouflaged on sandy bottoms.