Here in SoFla we call them "thorny oysters" and they are abundant,
especially on wrecks.

I'm told they are all the same species (S. americanus) but the
variations between specimens is huge, mostly depending on substrate and
exposure to current.

Deep inside the wrecks, the spines are widely separated, long, and flat.
The shell has pronounced curvature and is generally white.

On exposed areas of the reef, the spines are close together, short, and
rounded. The shell is flatter and dark red to light orange.

m

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