Appearance
As their common name implies, O. ceratophthalmus possess eyestalks extending beyond the eyes into long points, which are longer in adults, and shorter (or even absent) in juveniles. The crabs have a box-shaped body, 6–8 centimetres (2.4–3.1 in) across the carapace, with a darker markings towards the rear in the shape of an H. The outer edges of the eye-sheaths are also sharp and broadly triangular and distinctly pointing sideways in larger individuals. O. ceratophthalmus can run at speeds of up to 2.1 metres per second (6.9 ft/s).
The characteristic "horned" eyes of O. ceratophthalmus are not unique to the species, with other crabs sharing the characteristic, including O. cursor, O. gaudichaudii, O. macrocera, O. mortoni, O. rotundata, and O. saratan.