[3] These crabs are primarily grey, but have two basic color and size types for patch markings: pale and dark.

In both forms the color of the dorsal carapace tends to be darker toward the front, fading and becoming more sparse toward the back, while the underside of the crab is white.

The legs and claws are white with red to purple pigmentation to the same degree and hue as the carapace.

[6] Less dominantly, female control over receptivity in relation to male presence could influence the outcome of sexual selection during the breeding period.

[7] It has also been shown that during development the embryos begin to form osmoregulatory functions from the earliest embryonic stages of these crustaceans.

This crab has been identified throughout the length of New Zealand, but found more abundantly on the southern shores because the species O. truncatus replaces it in the north.

[3] H. sexdentaus has relatively few fish predators, but has been found in the stomachs of rig, red cod and sea perch.