Anadara ovalis Brugière, 1789
The comb-like hinge teeth are visible at the center of the bottom photo.
Often found along the coast anywhere from Massachusetts to the West Indies and Brazil, the Blood Ark is a white bivalve. The shell frequently appears to have dark brown fur growing on the lower two-thirds of it. This is actually the periostracum, a covering of noncalcareous material. The shell grows to a length of approximately two inches, and is fairly thick and sturdy. Each of the two valves has approximately 35 radiating ribs. The complete bivalve, when viewed from the end, is heart-shaped.
On each valve, along the hinge line there are small protuberances (“teeth”). They are flattened and narrow near the beak, and larger and angled farther out from the beak. (The beak or umbo is the rounded, pointy, prominent part of the bivalve shell located above the hinge.)
The creature inside is interesting in that it is one of the few mollusks having red blood. It is sometimes called the Bloody Clam. It lives in mud and sand in water from the low-tide line to a depth of ten feet.