ABSTRACT Recent studies show that the allometric relationships between hermit crab chelipeds and cephalothorax can be affected by the type of shell occupied, and that this relationship probably results from poorly fitting shells restricting the overall growth of crabs (the stunting hypothesis). The extent of this phenomenon in natural populations is unclear. In this study, discriminant function analysis was used to test whether the shell species occupied by individual Pagurus longicarpus could be predicted based on crab morphology. The relative cheliped size of male hermit crabs varied among shell species; crabs occupying shells of Nassarius vibex and Turbo castanea had the smallest chelipeds, and those occupying shells of Polinices duplicatus had the largest. These patterns were inconsistent with the stunting hypothesis because there was generally not an association between the relative size of a crab's gastropod shell and its cheliped morphology. When such an association was present, crabs occupying relatively large shells had relatively large chelipeds; the opposite pattern is predicted by the stunting hypothesis. The relationships predicted by the stunting hypothesis may not have been seen because the crabs may not have occupied their shells long enough for the effect to occur. The observed patterns were consistent with a hypothesis that suggests cheliped morphology and shell species occupancy change ontogenetically, creating an apparent relationship between shell species and cheliped shape.