brachyuran

…crabs—those belonging to the infraorder Brachyura, such as fiddler crabs, snow crabs, and ghost crabs—characteristically exhibit lateral movement. Other crustaceans in the same arthropod order (Decapoda) but belonging to the infraorder Anomura, such as hermit crabs, king crabs, and porcelain crabs, generally move forward or backward. Among the