Halogenated scleroproteins in the jaws of Viviparus fasciatus (Muller) (Gastropoda, Prosobranchia): iodine memory?

The jaws of Viviparus fasciatus have been studied with respect to morphology, histological and cytological structure and nature as shown by histochemistry and by three different methods of microanalysis. The <<brushlike>> pattern is the result of the juxtaposition of stiff rods, each one elaborated by one epithelial cell. Their small size, compared with previously studied marine species, enable us to better understand their makeup, The hard parts are issued from a transitory change of the secretory program of the buccal epithelium so that they are inserted between a superficial cuticle and a bed plate, or sole in which they remain fixed. The embedding cuticular material is chitinous. The jaw elements are formed by a tyrosin-derived scleroprotein whose tanning process is confirmed by a correlative halogenation with iodine and bromine concentrations. This noteworthy process concerning a fresh-water mollusc appears at a level comparable to the one found in marine species such as Haliotis. Added to their structural similarity, this allows us to appreciate the homology of various gastropod maxillary parts.