Colochirus robustus is roughly cylindrical with 5 shallow longitudinal ribs and grows to about 7 centimetres (2.8 in) in length. It has an angular appearance and finger-like or thorn-like protuberances on the ribs. At the anterior end is a ring of about eight large, feathery feeding tentacles. There is a slight transverse indentation near the rounded posterior end. There are three rows of tube feet on the underside. The colour is a vivid yellow, sometimes with grey between the ridges.