About Colochirus quadrangularis Troschel, 1846
Colochirus quadrangularis is a moderate-sized sea cucumber that reaches about 10 cm (4 in) in length. Its roughly cylindrical body has four longitudinal ridges, which give it a square cross section and a flat base. Irregular, soft, thorn-like projections called papillae lie along these ridges. The leathery body wall is reinforced by calcareous spike-like structures; this species specifically has basket-shaped spicules and perforated ellipsoids. The mouth is surrounded by a ring of large, branched feeding tentacles. Three rows of red tube feet run along the underside of the body, which tapers toward the posterior end. The anus is surrounded by 5 tooth-like projections. Its body is mainly grey, often with pink colouring on the ridges and papillae, and yellow or reddish tentacles. Colochirus quadrangularis can be confused with the similar pink warty sea cucumber (Cercodemas anceps), but Cercodemas anceps has low, warty protuberances covering its body instead of thorny projections. Colochirus quadrangularis is found in the tropical Indo-Pacific region, at depths down to about 115 metres (377 ft). Its range extends from East Africa and Madagascar to Malaysia and northern Australia. In Singapore, this species experiences unexplained population swings, sometimes being abundant and other times scarce. Colochirus quadrangularis is collected for the aquarium trade, but it is difficult to keep in a reef aquarium due to its specialist feeding requirements.
