Like the lobsters, some terrestrial crabs and other crayfishes, the Australian red claw crayfish, Cherax quadricarinatus, elaborates in its stomach wall calcium storage structures called gastroliths. For understanding the cyclic elaboration and stabilization of these amorphous calcified structures, we studied the organic matrix (OM) of these paired biomineralizations. After decalcification with acetic acid, we analysed the proteinaceous components of an acetic acid-insoluble fraction by two-dimensional electrophoresis. Nine spots were digested by trpsin and the tryptic peptides were sequenced by nanoLC-nanoESI-MS/MS mass spectrometry. About 100 peptidic sequences were compared to sequences previously registered in the databases. Seven of the partially sequenced organic matrix polypeptides are probably new proteins. Another one corresponds to the previously sequenced protein, GAP65, from Cherax quadricarinatus and the last one, which migrates in electrophoresis at around 25 kDa, presents strong homology with the crustacyanin-A2 subunit of Homarus gammarus.