Sharnia burnhamensis was a rare true crab from the Essex London Clay. It would have lived on the seabed as a mobile benthic animal, probably feeding opportunistically on small invertebrates and scavenged food.

Rare species such as Sharnia are important because they show that the London Clay ecosystem contained more than just the familiar common crabs and lobsters. Even unusual or locally scarce forms contributed to the remarkable variety of early Eocene crustacean life.