Blood Ark

lunarca ovalis

The Blood Ark (Lunarca ovalis) is a fascinating marine bivalve named for a highly unusual trait: it possesses red blood. Unlike most mollusks, which have clear or bluish, copper-based blood, the Blood Ark utilizes intracellular hemoglobin to transport oxygen. This remarkable adaptation allows the clam to thrive in low-oxygen, murky environments such as muddy bays and estuaries along the western Atlantic coast. Covered in a dark, fibrous coating that makes it resemble a fuzzy stone, this resilient clam is a quiet but vital part of coastal ecosystems, tirelessly filtering the water and serving as a nutrient-rich food source for various marine predators. Spot a Blood Ark? Identify it instantly with the Snappit nature app.

Habitat: Found in shallow, sandy, or muddy coastal waters and estuaries, typically from the intertidal zone down to a few meters deep.

Appearance

The Blood Ark features a thick, rounded, somewhat heart-shaped shell that typically grows to about 4 to 6 centimeters in length. Its white shell is heavily sculpted with 26 to 35 prominent, radiating ribs. In life, the shell is largely covered by a thick, dark brown, and distinctly hairy or fibrous outer layer called the periostracum, which often wears away near the hinge to reveal the white shell beneath. When opened or damaged, the clam reveals its striking, bright red, hemoglobin-rich tissues and fluids.

KingdomAnimaliaPhylumMolluscaClassBivalviaOrderArcidaFamilyArcidaeGenusLunarca

Blood Ark

Interesting facts

Because they can survive in oxygen-poor waters, Blood Arks can thrive in muddy, stagnant habitats where many other species of bivalves would suffocate.

The Blood Ark is one of the very few mollusks that bleed red, thanks to the presence of intracellular hemoglobin, functioning much like the blood in vertebrates.

Their scientific genus 'Lunarca' loosely translates to 'moon ark', referring to the clam's rounded, lunar-like shell profile.

Their thick, hairy periostracum often causes beachgoers to mistake them for fuzzy rocks when they are partially buried in the sand.

Special abilities

Unlike most bivalves, it uses iron-based hemoglobin to transport oxygen, allowing it to survive in hypoxic (low-oxygen) mudflats.

A thick, hairy outer shell layer (periostracum) helps the clam blend into muddy substrates and protects the calcium carbonate shell from acidic sediments.

The heavily ribbed shell margins interlock tightly when closed, creating a formidable defense against prying predators like crabs and sea stars.