Signs of claw asymmetry appear in a homochelate crab

Lateral asymmetry is observed widely among vertebrates and invertebrates. It appears in various aspects, such as morphological structure, or the preferential use of body parts. Many studies have focused on animal handedness and its developmental process. This is especially true in crabs with asymmetrical claws (heterochelate), while there are few studies on handedness (claw laterality) in crabs with symmetrical claws (homochelate). In this study, we analyzed the claw symmetry of the Chinese mitten crab (Eriocheir sinensis) by comparing the ratio of chela height to length (HL-ratio), and we also analyzed the correlation between cheliped morphology and weight, crab body weight, physiological indices and closing force. The relationship between handedness and behavior of the crabs was further analyzed. The results showed that the morphology of the chelipeds was not symmetrical. The left chela of male crabs and the right chela of female crabs were stubbier. The closing force was positively correlated with the HL-ratio. Moreover, the closing force of the right cheliped was significantly greater than that of the left cheliped in females. In the comparison of behaviors between the lateral group (crabs with significantly greater closing force on the left or right claw) and non-lateral group (crabs with roughly the same closing force on their left or right claws), we identified that the lateral group showed more significant lateralization than the non-lateral group in hiding behavior. Further studies are needed to investigate the mechanism or evolutionary drivers of asymmetric claws in homochelate crabs.