Ontogenetic and positional variation in denticle morphology of Metacarcinus magister (Dungeness crab)

Abstract

Decapod crustaceans, specifically crabs, use specialized feeding appendages called chelae for a range of functions, the foremost of which is prey capture and handling. The gross morphology of the chelae and denticles, the tooth-like structures along the pincher fingers, may provide information about prey selection and foraging behavior. We measured the aspect ratio (height/width) and radius of curvature (radius of the tooth tip) of the denticles on the chelae of Dungeness crab, Metacarcinus magister. Our specimens were collected from Friday Harbor in the San Juan Islands, Washington and varied in size from 6-21 cm carapace length. We examined denticle morphological changes in an ontogenetic series as well as along the length of the immobile finger, propus. We found that as M. magister matures, their denticles became overall taller and pointier as represented by higher aspect ratio morphology. Variation in denticle morphology in the ontogenetic series appears to be directly related to shifts in diet with age. Along the propus length, denticles were broad and molariform in the center and more pointed nearest the fulcrum and tip. The layout of various shaped denticles along the propus indicates that both crushing as well as peeling or piercing feeding techniques are used by M. magister. This study prompts further research into the effect of predatory feeding appendages on prey populations and morphologies.