The carapace of C. atlas is relatively smooth and somewhat flattened, with a width typically greater than its length. A key feature of this species is its flattened, paddle-like legs, particularly the last pair of walking legs (fifth pereopods). These legs have a widened shape that resembles paddles, which helps the crab swim and move quickly through soft substrates. The claws are strong but relatively small compared to other crabs of similar size. They are equipped with small, sharp pincers that allow the crab to grasp and manipulate prey items. C. atlas generally has a sandy or brownish coloration. The eyes are small and positioned on short stalks. The antennae are small. The body of C. atlas is relatively streamlined, aiding its ability to burrow quickly into sand or mud.