The carapace is generally rounded, smooth, and often somewhat domed, with a width slightly greater than its length. It provides a solid structure that supports the crab’s habit of carrying sponges or other materials. Like other sponge crabs, T. dormia has modified hind legs (fourth and fifth pereopods) that are specialized for grasping and holding objects. These legs are often shorter than the others and adapted for the crab’s unique behavior of lifting and securing items on its back for camouflage. The claws are typically large and strong, with the larger claw adapted for defense and the smaller one used for feeding. The crab generally has a muted color palette that matches the surrounding substrate and materials it carries, often a blend of browns, greys, and whites.