Dinocardium robustum (John Lightfoot, 1786) Atlantic Giant Cockle

    This medium sized (about 80 mm.) specimen was photographed while sitting in a shallow tide pool at the base of granite rocks of the south St. Johns River jetty at Mayport Naval Station beach during a minus tide on 1/8/2008. For no apparent reason, the specimen began violently thrashing around - a behavior that recurred periodically over a period of several  minutes. A selection of images taken over a period of six seconds is presented below. Another smaller specimen present on the open Atlantic beach was performing a similar thrashing action. Neither specimen appeared to have accomplished anything by its behavior.

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