Belanger Lab: Libinia emarginata

	Libinia emarginata
	Libinia emarginata crabs (Leach, 1815) are portly spider crabs (Decapoda, Heterotremata. Majoidea). They belong to a group of animals currently thought to be among the first to have evolved the crab form (Rice, 1980). Unlike many crabs, which have five larval stages, Libinia has only two. Libinia's skeleton is heavily calcified and decorated with spines that serve as armour. The presence of nine longitudinal bumps distinguishes Libinia emarginata from the longnosed spider crab (Libinia dubia) which only has six such bumps and a pronounced v-shaped rostrum. Libinia crabs walk forward about 80% of the time in a slow and jerky manner. These crabs are scavengers that live in estuarine waters off the Atlatic coast from Nova Scotia to Brazil. They can be found from shore to depths of 125 m. (Perry and Larsen, 2004). We compare forwards and sideways walking in Libinia to itself and other crustaceans in order to understand how the different components of walking need to be modified during the performance of this behavior. Below is a clip of Libinia crabs walking forwards.

	Libinia crabs can grow up to 12cm or longer. The females have smaller claws (less calcified). Small crabs are not as heavily calcified as the adults and tend to bury themselves in the sand to avoid predation. As the crabs grow larger their parasite load increases considerably. These crabs have a terminal molt after which no further molt is possible which possibly contributes to the observed deterioration in skeleton integrity after they reach certain size.
	Below is a tree of proposed crustacean relationships based on muliple approaches (Martin and Davis, 2001). We show the species we study plus the other brachyuran shown to walk forwards (the soldier crab, Mictyris).