Appearance
Large males may reach a carapace size of 20.5 by 17.5 millimetres (0.8 in × 0.7 in), and is brownish-yellow in colour. The carapace becomes narrower towards the front of the animal, and is often concealed by epibionts. I. phalangium resembles the closely related species Inachus dorsettensis, but has less prominent spines on the carapace.

