Formation of the Periostracum in Mercenaria mercenaria.

A series of histochemical tests performed on the mantle of the northern quahog Mercenaria mercenaria L. suggest that the epithelium of the inner surface of the first fold and the underlying secretory cells function together in the formation of the periostracum in this mollusk. The secretory cells supply a phenolic substrate which, when oxidized, provides quinones capable of tanning the periostracum.