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RESEARCH PRODUCT

Further comments on the origin of oysters

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In his comment to our recent paper (Marquez-Aliaga et al. 2005), Hautmann (2006) raises two interesting questions: (a) the ambivalent attachment to the substrate recognized in the species cristadifformis Schlotheim, 1820 and spondyloides Schlotheim, 1820, which we include into the Ostreoidae genus Umbrostrea, is in conflict with the sinistral attachment usually recognized as an autapomorphy of the group and (b) antimarginal ribs are not valid as a character linking Prospondylus acinetus Newell and Boyd, 1970 and early oysters (our proposal of derivation), because they appear in several unrelated families of bivalves. Moreover, Hautmann (2005), finds additional difficulties in accepting our hypothesis of descent of oysters from the Prospondylidae because, contrary to the latter group, (c) oysters, in general, do not develop a pallial line; (d) the resilifer of the right valve is in high relief and flanked by two depressions and the ligamentary area of the left valve impresses such shape; (e) the microstructure of the inner shell layer of prospondylids (crossed-lamellar) is different from that of early oysters (probably nacreous); (f) too few data are known from the internal morphology