The Regulation of Interspecific Variations of Shell Shape in Bivalves: An Illustration with the Common “Clams” Fauna along French Coasts

I report an unexpected negative covariance occurring between two major parameters governing shell growth in marine bivalves, especially within the order Veneroida. This relationship is highlighted, here, considering a set of forty, rather common species of clams collected from French coasts. Interestingly, this negative covariance has two (geometrically related) consequences on the pattern of variation of shell shape at the inter-specific level: