<Li> Eubrachyura <Ul> <Li> Heterotremata </Li> <Li> Thoracotremata </Li> </Ul> </Li> <Ul> <Li> Heterotremata </Li> <Li> Thoracotremata </Li> </Ul> <P> Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) (Greek: βραχύς, translit . brachys = short, οὐρά / οura = tail), usually entirely hidden under the thorax . They live in all the world's oceans, in fresh water, and on land, are generally covered with a thick exoskeleton and have a single pair of claws . Many other animals with similar names--such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, and crab lice--are not true crabs . </P> <P> Crabs are generally covered with a thick exoskeleton, composed primarily of highly mineralized chitin, and armed with a single pair of chelae (claws). Crabs are found in all of the world's oceans, while many crabs live in fresh water and on land, particularly in tropical regions . Crabs vary in size from the pea crab, a few millimetres wide, to the Japanese spider crab, with a leg span of up to 4 metres (13 ft). </P>

Is a crab a fish or a mammal
find me the text answering this question