Decapoda

Decapoda is an order of crustaceans within the class Malacostraca, comprising many familiar aquatic species such as crabs, lobsters, crayfish, and shrimp. The name derives from Greek deka (ten) and pous (foot), referring to the ten thoracic limbs that typically function as legs.

Anatomy and morphology

Most decapods have a cephalothorax, formed by the head and thorax, usually covered by a hard carapace, and an abdomen bearing pleopods and ending in a tail fan. The first pair of thoracic legs is often enlarged as chelae (claws). They possess various mouthparts including maxillipeds, and their gills are adapted to their aquatic lifestyle. Like other crustaceans, decapods grow by molting their exoskeleton. Their limbs are generally biramous, meaning each leg branches into two parts.

Classification

Decapoda is divided into two main suborders: Dendrobranchiata (prawns) and Pleocyemata (the majority, including true shrimps, crabs, lobsters, and crayfish). Pleocyemata further encompasses groups such as Caridea (caridean shrimps), Astacidea (crayfish and true lobsters), and other lineages that include crabs and related forms. Most decapods are marine, but several lineages have adapted to freshwater environments, and a few have terrestrial or semi-terrestrial habits.

Life cycle and ecology

Reproduction varies among groups. In Pleocyemata, females typically brood eggs on the abdomen until hatching. Larval development can include free-swimming nauplius, zoea, or mysis stages in many species, though some have direct development. Ecologically, decapods occupy a broad range of habitats from deep oceans to rivers and estuaries. They play important roles in food webs and are valuable as seafood, supporting commercial fisheries in many regions. Some species are invasive or threatened due to overfishing, habitat loss, or climate change.