CrustaceansCrustacea

Crustaceans are marine invertebrates characterised by a rigid, chitinous exoskeleton, segmented bodies, and jointed appendages. Most species feature a cephalothorax covered by a carapace, followed by a segmented abdomen. Body forms vary widely, from the robust crabs and lobsters to the laterally flattened amphipods and dorsoventrally compressed isopods. Sizes range from tiny copepods less than 1 mm (0.04 in) to large lobsters exceeding 50 cm (20 in) in length and crabs with similar leg spans.

They inhabit diverse marine environments, including coral reefs, rocky shores, sandy bottoms, and seagrass beds, found from the intertidal zone down to over 100 m (330 ft) depth. Diet varies significantly by species; many are scavengers, some graze on algae, others filter-feed, and certain groups are active predators. Many are cryptic or nocturnal, sheltering in crevices, under rocks, or in burrows during daylight hours and emerging to forage after dark. Growth occurs through ecdysis, the periodic shedding of their rigid exoskeleton.