Cyrtopleura costata Linnaeus, 1758
The bottom photo shows the spoon-shaped apophysis extending from under the beak.
The lovely white Angel Wing is a type of Piddock shell. Despite the delicate beauty of this thin, brittle shell, the clam is able to bore into wood, clay, and even shale and gneiss rocks. This boring or abrasion is accomplished by the anterior end of the shell which is rocked back and forth by the suctionlike foot. Jets of water from the mantle cavity flush particles from the hole being bored.
The elongated shell may reach a length of an impressive seven inches. Angel Wings are usually white, though occasionally a pink-tinged one is found. The pinkness is likely the result of the clam's having been exposed to Red Tide algae.
The surface of this bivalve shell has approximately 26 radiating ribs; the ribs near the front end of the shell (the boring end) are taller and have sharper fluted scales than those which cover the rest of the ribs. Growth lines (slight furrows) run horizontally over the surface of the shell. The two valves of the clam gape, touching only at a point near the top of the shells. The Angel Wing has a shelly brace (a spoon-shaped projection) under the the pointy “nose” (beak) of the shell. This brace is called the apophysis, and is the location at which the mollusk's foot muscles are attached. Near the beak, and to the anterior of the beak, a part of the shell curves back up over the exterior surface.
Cyrtopleura costata has long, fused siphons which protrude from its burrow. The siphons circulate water and suspended ocean matter down to the creature's gills. The clam cannot retract the siphons into its shell, and the two valves of the shell cannot completely close. The muscles holding the valves together are weak, so it is rare to find a dead Angel Wing clam with both halves still connected. Some shell hunters dig for the living clam, which dwells in stiff material to help hold itself together. When fresh, the mollusk is covered with a thin grayish periostracum.
In the West Indies the clam is a staple food item. It may be found from there to Brazil, and from Cape Cod to the Gulf of Mexico, although it is uncommon north of Virginia. It lives in shallow water, sometimes as much as three feet deep in the mud.