<p>Dendostrea frons (Lamarck, 1819) - interior of a left valve of the frond oyster, 5.9 cm across at its widest.  Frond oyster shells vary in shape, which is dictated by the nature of the encrusted substrate - usually gorgonians ("soft corals").  This individual had encrusted an upright gorgonian.
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Family Ostreidae (Triassic to Holocene) - the oysters are filter-feeding, epifaunal, hard substrate encrusters that sometimes form reefs.  They occupy tropical to temperate estuarine and shallow-water marine settings.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/47445767@N05">James St. John</a>
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<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/jsjgeology/15568052914/">Dendostrea frons (frond oyster) (San Salvador Island, Bahamas) 2</a>