Rock-limpets

Rock-limpets were bivalves (freshwater molluscs) found in various parts of the Edgeworld. They made no direct appearance, but in The Last of the Sky Pirates, Rook said "I do know this place Xanth... Wilderness Lair it's called. The mighty Sky pirate fleets used to take refuge here, clinging to the cliff-face like rock-limpets."