Cockles and Angelwings

Published: Tuesday, December 24, 2013 at 09:59 AM.

You probably remember the old song about Molly Malone singing, “cockles and mussels, alive, alive oh!”  As Molly was pushing her wheelbarrow, the cockles she was selling were not our Van Hyning’s cockle, but the common European cockle, Cerastoderma edule, or any of several small cockle-like clam species that are harvested using rakes at low tide. Cockles are still available at seaside stalls in the United Kingdom. Our own giant cockles are edible also and the reddish flesh makes fine chowder. However, few people go to the trouble to harvest our giant cockles. For a bit of trivia, cockles are even mentioned in the Magna Carta. That historic document granted English subjects the right to collect up to eight pounds of cockles from the shore without hindrance or confiscation.

Our beaches have several other smaller shells that are classified in the same family as the giant cockle. One can easily find shells of the Atlantic strawberry cockle (Americardia media), spiny papercockle (Papyridea soleniformis), Florida pricklycockle (Trachycardium egmontianum), and even the smooth-shelled common egg cockle (Laevicardium laevigatum).

Much sought after by collectors this time of year is the delicate bright white shell of the angelwing (Cyrtopleura costata). More common on the Atlantic or southwest coasts of Florida, nevertheless angelwings are commonly found on Cape San Blas beaches. To be so fragile and elegant, it seems surprising that these bivalves live burrowed into muddy clay deposits offshore. They can also be found in St. Joseph Bay where there are muddy clay bottoms. They need the stiff muds for support because the muscles holding the two shells together are quite weak. In fact, this clam cannot fully close its shell making it susceptible to extreme environmental changes. With its muscular foot, the animal digs a burrow in the stiff muds and projects two siphons just above the surface of the substrate. Once in place it pumps water through the siphons to filter suspended food particles. In life, the burrows and gaping valves of this animal provide a refuge for several species of small mud crabs. Even the abandoned burrows provide a home for other sea creatures long after the angelwing has departed.

Since these clams are adept at boring into stiff clays, it is not surprising that they are closely related to shipworms, which are not worms at all but boring clams. You have probably inspected their tunnels winding through pieces of driftwood thrown up on the beach.

More commonly found on Panhandle beaches are the Campeche angelwings (Pholas campechiensis). Occasionally, one finds the little false angelwing (Petricolaria pholadiformis). While true angelwings can grow a shell almost six inches long, false angelwing shells only reach a two inch maximum.

So whether you are a shell collector or just like to look for pieces of polished beach glass, the “winter beach” is a great time to stroll our beaches.

Tom Baird has been a fisheries biologist, high school and community college teacher (oceanography and microbiology), director of a science and environmental center, teacher of science and principal in Pinellas County as well as an educational consultant. He retired from the Florida Department of Education and he and his wife divide their time between Tallahassee and Cape San Blas.



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