Oligochaetes are segmented worms and most have a spacious body cavity (coelom) which is used as a hydroskeleton. They range in length from less than 0.5 millimetres (0.020 in) up to 2 to 3 metres (6.6 to 9.8 ft) in the 'giant' species such as the Giant Gippsland Earthworm and the Mekong Worm "Amynthas mekongianus".