Appearance
The body of this crab is quite hairy, and has a whitish to cream colour, with purple marks on the carapace. The carapace has a smooth texture and a fringe of long setae. It is significantly wider than it is long, growing up to 5 cm long and 6.3 cm wide. The postero-lateral margins strongly converge.
A. undecimdentatus is often very dirty which can alter its appearance. It has short antennae, being only about a quarter of the length of the carapace. The claws are similar to each other, with black tips. Both the claws and legs have many bristles.
This crab is sometimes mistaken for the more common Atelecyclus rotundatus. However, A. rotundatus can be distinguished by its finer granulations and narrower carapace.