decapod

Decapods, or decapod crustaceans, are an order (Decapoda) within the class Malacostraca. The name derives from ten legs (pereiopods) used for walking, feeding, and handling. Decapods comprise many familiar and economically important crustaceans, including shrimps, prawns, lobsters, crabs, and crayfish. There are about 15,000 described species, with a global distribution in marine and freshwater environments and in some tropical terrestrial habitats.

Anatomy and morphology typically include a segmented body with a cephalothorax protected by a carapace and an abdomen bearing swimmerets. The five pairs of thoracic legs are usually used for locomotion, and the first pair is often modified into large claws (chelae) in many groups. The abdomen ends in a tail fan formed by uropods and the telson in some lineages. Gills are adapted to branchial chambers, and most decapods molt their exoskeletons as they grow.

Classification and reproduction are organized into two major suborders: Dendrobranchiata (prawns) and Pleocyemata (the rest, including true shrimps, crabs, lobsters, and crayfish). In Pleocyemata, females brood eggs on the abdomen until hatching; in Dendrobranchiata, eggs are released and free-swimming nauplius larvae develop in the water. Within the order, groups such as Caridea (true shrimp), Astacidea (crayfish and lobsters), and Brachyura (true crabs) represent major lineages.

Ecology and economy: Decapods inhabit a broad range of habitats from coral reefs and seagrass beds to freshwater rivers and estuaries. They perform diverse ecological roles as scavengers, herbivores, and predators. Many species are economically important for food and aquaculture, including lobsters, crabs, and penaeid shrimps, while others are subjects of fisheries management and biodiversity research. Some decapods are introduced outside their native ranges and can impact local ecosystems.