Squat lobsters are dorsoventrally flattened
crustaceans with long tails held curled beneath the thorax. They are found in the two superfamilies
Galatheoidea and
Chirostyloidea, which form part of the
decapod infraorder
Anomura, alongside groups including the
hermit crabs and
mole crabs. They are distributed worldwide in the oceans, and occur from near the surface to deep sea
hydrothermal vents. More than 900 species have been described, in around 60 genera. Some species form dense aggregations, either on the sea floor or in the water column, and a small number are subject to commercial fishery.