DEMINERALIZATION MECHANISM OF BORING GASTROPODS 73 



to those illustrated for the same species of ovster bv Tsujii et al. 

 ( 1958) and Watabe et al ( 1958), were observed. 



Structural alteration of the calcitic and aragonitic nacreous shell 

 of three different species of bivalves and one species of gastropod 

 by the secretion of ABOs from four different species of borers was 

 similar so far as could be determined by inspection of the electron 

 micrographs. Etched areas showed a variety of structural configura- 

 tions, depending primarily upon the depth to which the superficial 

 damage had progressed (Figs. 12 to 15, 17, and 19). Earliest evi- 

 dence of surface alteration appeared as a slight generalized pitting. 

 In more severely damaged regions the pits appeared larger and 

 varying amounts of loosened mineral material were remo\ ed on the 

 replicas. It was often necessary to take several replicas from a deeply 

 etched area before enough of the loosened detritus was removed to 

 provide a faithful reproduction of the firm underlying surface. At 

 this level, widespread pitting and some crystal outlines were ob- 

 served, but it was not possible to determine whether there was any 

 preferential activity of the ABO secretion on the mineral or the 

 organic constituents of the shell. 



The most informative preparations pro\ ed to be the preliminary 

 pseudo replicas, on which the adherent loosened crystal outlines 

 could be examined in some detail (Figs. 20 to 25). The moth-eaten 

 appearance of these crystals (see especially Figs. 21 and 25), as 

 well as their serrated edges (see especially Figs. 20, 21, and 25) 

 and the wide intercrystalline spaces, strongly suggests that these 

 crystals underwent a marked degree of surface solution, and that 

 loosening resulted from damage to the crystals rather than to the 

 supporting organic matrix. 



Figs. 12 to 15. Electron micrographs of areas of the nacreous surfaces of 

 mollusk shells subjected to activity for 24 hours in vitro of ABOs placed 

 directly on the specimens. The replicas from which these pictures were made 

 represent the true surfaces after loosened debris had been removed by taking 

 several preliminary replicas. Varying degrees of early pitting and roughening 

 are shown, (x 6000.) 



Fig. 12. ABO of Urosalpinx cinerea folhjensis on Murex fulvescens. 



Fig. 13. ABO of Sininn perspectiviim on M. fulvescens. 



Fig. 14. ABO of U. c. foUijensis on Dosinia discus. 



Fig. 15. ABO of U. c. foUijensis on Crassostrea virginica. 



