Transverse Ark (also known as Transverse Ark Clam)
Phylum: Mollusca, Class: Bivalvia, Order: Arcida, Family: Arcidae, Genus: Anadara, Species: A. transversa · Arcidae (Ark shell family) · Bivalve, whole single valve, oval to rectangular fan shape
Species
Anadara transversa
Shell Type
Bivalve, whole single valve, oval to rectangular fan shape
Family
Arcidae (Ark shell family)
Size
Approximately 1 to 1.5 inches in length, which is average for this species. Adults typically range from 0.75 to 1.5 inches.
Color & Pattern
Off-white to grayish-brown exterior with prominent, regular radial ribs crossed by fine concentric growth lines. The color is somewhat sun-bleached and typical of beach-worn specimens found along the coast.
Rarity
Common, frequently found beachcombing along the North Carolina coast.
Habitat
Shallow marine and brackish waters, typically found burrowing or byssally attached in soft bottoms, mudflats, and sand substrates from the intertidal zone down to shallow subtidal depths.
Geographic Range
Western Atlantic Ocean, extending from Massachusetts south along the United States coast to Florida, the Gulf of Mexico, the Caribbean, and occasionally down to South America.
Description
A sturdy, compact bivalve shell with a distinctive asymmetrical, elongated shape. It features strong, prominent radial ribs radiating from the umbo across the exterior surface, creating a textured, grid-like pattern when intersected with fine concentric lines. The hinge line is straight with a series of small, interlocking teeth typical of ark shells.
Key Features
Straight hinge line with numerous taxodont teeth, prominent radial ribs (usually around 30 to 35), and an inequilateral trapezoidal or rectangular outline where the posterior end is elongated.
Collector Value
Low to moderate commercial value, highly accessible for beginner shell collectors and beachcombers. Excellent for educational collections or crafts rather than high-end displays.
Condition Notes
Fair to Good condition single valve. Shows signs of natural weathering and sun-bleaching typical of beach specimens, but the structural integrity and radial ribs remain well-defined.
Interesting Facts
Unlike many clams that completely bury themselves and lose mobility, ark shells use a strong, fibrous structure called a byssus to anchor themselves to hard objects or rocks on the seafloor, living a semi-sessile lifestyle.
Ecological Role
As suspension feeders, ark shells filter phytoplankton and organic particles from the water column, helping to clear water and cycle nutrients. They serve as an important food source for marine predators such as whelks, rays, and bottom-feeding fish.
Similar Species
Blood Ark (Anadara ovalis) and Turkey Wing (Isognomon alatus). The Transverse Ark is distinguished from the Blood Ark by its smaller, more elongated and trapezoidal shape with fewer ribs.
Beach Finding Tips
Look along high-tide shell lines on sandy or shelly North Carolina beaches, especially after storms or strong winds. Check around tidal inlets and mudflat edges.
Notes
NC beaches