The
decapoda or
decapods (literally "ten-footed") are an order of
crustaceans within the class
Malacostraca, including many familiar groups, such as
crayfish,
crabs,
lobsters,
prawns and
shrimp. Most decapods are
scavengers. The order is estimated to contain nearly 15,000 species in around 2,700 genera, with around 3,300 fossil species. Nearly half of these species are crabs, with the shrimp (about 3000 species) and
Anomura (including
hermit crabs,
porcelain crabs,
squat lobsters (about 2500 species) making up the bulk of the remainder. The earliest
fossil decapod is the
Devonian Palaeopalaemon.