Cyclocorystes pulchellus was a relatively small true crab that lived on or close to the sea floor. It was probably an opportunistic feeder, picking up small invertebrates, carrion and organic material from the muddy bottom rather than specialising on a single food source.

Small crabs like this would have been important links in the London Clay food web. They helped recycle dead material, preyed on even smaller animals and in turn provided food for fish and larger predators. Its ornate shell also shows how diverse crab body shapes had become by the early Eocene.