The portly spider crab, Libinia emarginata, is a species of crab found in estuarine habitats on the east coast of North America from Nova Scotia to the Gulf of Mexico. This crab grows to about 10 cm (4 inches) across its back, which is spiny and often covered with a "garden" of sponge and seaweed. The carapace is shiny, covered with short hairs, and its color varies from brown to a dull yellow; the tips of the claws are white. The hairs on the shell attract algae, barnacles, and debris. It likes to camouflage after moulting. The portly spider crab is very slow moving, and is a scavenger.

The portly spider crab is generally not considered edible, unlike the blue crab which is often found in the same waters.