CONSTRUCTIONAL MORPHOLOGY AND CUTICULAR MICROSTRUCTURE OF EXTANT AND FOSSIL CRAB CLAW DENTICLES

The morphology of decapod crustacean chelae has been the subject of extensive research. Chela morphology is directly linked to the functional morphology of feeding and adaptations for more successful capture of skeletonized prey. These adaptations are in turn linked to the well-studied evolutionary escalation between certain crabs and mollusks. These aspects have been studied; however, the role that cuticular microstructure and composition of the chelae play in the functional morphology and phylogeny of crabs has not. To explore the extent to which cuticle microstructure of crab chelae affects these factors, we have examined the microstructure of two species of crabs, Scylla serrata Forskål and Callinectes sapidus Rathbun, each of which has extant and fossil representatives. Denticles and claw tips of certain extant crab claws are clearly more heavily calcified and durable than other parts of the cuticle; these differences often correspond to color differences in the denticles and tips of claw fingers. In order to identify these possible functional adaptations in the fossil record, it is necessary to demonstrate that these differentiated parts of the cuticle are preserved and recognizable in fossil material. To determine if these structures are preserved, a pair of fossil and modern claws from both species were sectioned to expose the denticles in cross section. The denticles are more densely calcified and are often separated from the remainder of the claw by an invagination of the exocuticle. Our results show that these distinctive cuticle compositions and architectures are robust enough to be recognizable in the fossil record in the two species examined. Thus, we can begin to explore how and when these cuticular and possible behavioral adaptations evolved. The phylogenetic significance of these structures can also be examined and included in our ongoing study of decapod cuticle as a taxonomic tool.