Unlike the giant squid, whose arms and tentacles have only suckers lined with small teeth, the colossal squid's limbs are also equipped with sharp hooks: some swivelling, others three-pointed. Its body is wider and stouter, and therefore heavier, than that of the giant squid. Colossal squid are believed to have longer mantles than the giant squid, but shorter tentacles.
The squid exhibits abyssal gigantism. The beak of M. hamiltoni is the largest known of any squid, and more robust than that of the giant squid. The colossal squid also has the largest eyes documented in the animal kingdom; a partly collapsed specimen measured 27 cm (11 in) in diameter, with a 9 cm (3.5 in) pupil. The eye was estimated to be 30 to 40 cm (12 to 16 in) when the squid was alive.