|Panopeidae and Menippidae were, until recently, in the family Xanthidae, which contained more genera of crabs than any other crab family. Recent revisions in taxonomy split the Xanthidae family into seven separate families. The crabs in these families are oval to hexagonal in shape, with a broad anterior, never with a protruding rostrum. Their last pair of legs are normal, not flattened into a flap to swim with. Some members of this family, none in our area, contain toxins in their exoskeleton. Most of these crabs are associated with colonial invertebrate colonies, such as corals, sponges, tunicates and bryozoans. The crabs in Texas' waters are mostly associated with oyster reefs, feeding off encrusting organisms and other small animals that take shelter between oyster shells. Only one of these crabs grows large enough to be a serious predator of the oysters, the stone crab with its huge claws capable of crushing the oyster shell into bits. Though these crabs are marine, the estuarine mud crab (Rhithropanopeus harrisii) has recently invaded several of Texas' freshwater reservoirs.