FISHERY BULLETIN: VOL. 82. NO. 1 



FIGURE8. — Microstructural variation in the shell of a 97.5 mm long, 92-yr-old ocean quahog, Arctica islandica. The central photograph is of an 

 acetate peel from a radial, polished, and etched section through the valve at the ventral margin. Black lines locate SEM photomicrographic 

 enlargements of specific polished and etched areas in the section valve (scale bar = 1 mm), (a) Periostracum ("P") with angular cavities and 

 HOM microstructure (scale bar = 10 /xm). (b) Cavities in HOM microstructure of outermost valve surface. White rectangle encloses are 

 enlarged in (c) (scale bar = 10 /mm), (c) Cavities showing bleblike ICM structures (scale bar = 1 jtim). (d) HOM microstructure at top trending to 

 ISP, then to transitional CA-CL toward the bottom. White rectangle encloses the area enlarged in (e) (scale bar= lOjum). (e) Transitional CA- 

 CL microstructure at higher magnification (scale bar = 10 ju.m). 



14 



