Anomura

Anomura is a diverse infraorder of decapod crustaceans, commonly known as asymmetrical crustaceans or, more broadly, as hermit crabs, king crabs, porcelain crabs, and squat lobsters. The name Anomura literally translates to "uneven tail," a reference to the often asymmetrical abdomen that is coiled or tucked beneath the thorax. This group is distinguished from true crabs (Brachyura) by several key characteristics, including the reduced size of the fifth pereiopod, which is often concealed, and the asymmetry of their abdomen.

The infraorder Anomura encompasses a wide array of species with varied lifestyles and appearances. Hermit crabs, perhaps the most well-known anomurans, are characterized by their soft, coiled abdomens that they protect by inhabiting discarded gastropod shells. King crabs, belonging to the family Lithodidae, are large and economically important crustaceans. Despite their common name, they are more closely related to hermit crabs than to true crabs. Porcelain crabs (Porcellanidae) are small, flat-bodied crabs that often resemble true crabs but possess a more flexible abdomen. Squat lobsters (Galatheidae and Chirostylidae) are also part of Anomura, often found in deep-sea environments.

Anomurans inhabit nearly all marine environments, from intertidal zones to the deep sea, and some species are found in freshwater or terrestrial habitats. Their diets are equally varied, ranging from detritivores and filter feeders to active predators. The evolutionary relationships within Anomura are complex, and ongoing research continues to refine our understanding of their phylogeny and the diversity within this fascinating group of crustaceans.