Calappidae and Hepatidae - Box Crabs
Some crabs of the Calappidae family have the ability to hide their legs and claws close to their shell, appearing box-like and inert, thus the name "box crabs". They are also known as "shame-faced" crabs for the way they hold their broad flat claws over the anterior region of their shell, as if hiding their face. Their claws are highly ornamental and are fringed with tiny hairs. It is believed that the hairs filter sand and other particles from water that is siphon into the body and across the gills to extract oxygen. This is useful when the crab is buried in the sediment. One claw has a specialized enlarged tooth that is used to "peel" open gastropod shells, similar to using a can opener.
The family Calappidae has recently undergone revision and its genera were split into four different families. Of those families, only Calappidae and Hepatidae are present in the Gulf of Mexico.