Crabs are fascinating crustaceans found in oceans, freshwater, and on land, characterized by their hard exoskeletons and distinct sideways walk. They belong to the order Decapoda, which means "ten-footed," referring to their five pairs of legs, the front pair often modified into strong claws used for defense and hunting. Crabs are omnivores, feeding on algae, plankton, and small marine animals. They play a crucial role in marine ecosystems, contributing to nutrient cycling and helping maintain the balance of marine life. Despite their tough exteriors, crabs periodically molt, shedding their shells to grow larger. Their unique anatomy and adaptability have made them a vital part of coastal biodiversity.