Morphological notes on Pinnaxodes gigas Green, 1992 (Brachyura, Pinnotheridae) emphasizing on length-weight relationship under multi-model approach

This study describes biometric characteristics of the pea crab Pinnaxodes gigas, a symbiont of the geoduck clam Panopea globosa in the eastern-central Gulf of California. Differences were observed in the coefficient of allometry when length-weight relationships (LWR) were analysed under a multi-model approach. The winner model for LWR in females was that exhibiting two phases ("two-segments" and "broken-stick"), while in males the models cubic and quadratic, presenting a continuous change in coefficient of allometry along all sizes, were chosen as the best. The relationships of carapace width, length and height were also tested for females with the two-segment model and the breakpoint was found at 20 mm carapace width for these three relationships. It is concluded that the breakpoint must be related to the size-at-maturity reached by females, and that these changes in dimensions correspond to an adaptation in the females shape for carrying the egg clutch.