Noah's Ark Shell (Ark Clam)
Phylum: Mollusca, Class: Bivalvia, Order: Arcida, Family: Arcidae, Genus: Arca, Species: Arca noae · Arcidae (Ark shell family) · Bivalve, whole shell, elongated trapezoidal shape with a prominent byssal gape
Species
Arca noae
Shell Type
Bivalve, whole shell, elongated trapezoidal shape with a prominent byssal gape
Family
Arcidae (Ark shell family)
Size
Approximately 1 to 1.5 inches in length. Adults typically range from 2 to 4 inches, making this a smaller juvenile specimen.
Color & Pattern
Striking zebra-like pattern of dark brown or chestnut alternating with white or cream-colored bands radiating from the beaks. The interior is whitish, sometimes showing brown markings near the margin.
Rarity
Common
Habitat
Found in shallow subtidal waters attached to hard substrates, rocks, or coral reefs using strong byssal threads. Primarily a marine species.
Geographic Range
Mediterranean Sea and the Eastern Atlantic Ocean, extending down to the coast of West Africa.
Description
An oblong, heavily ribbed bivalve shell with a distinctive straight hinge line and a wide, flat area between the beaks. The exterior features strong radial ribs crossed by fine concentric growth lines, creating a textured, checkered surface. The margin is scalloped to interlock tightly when closed.
Key Features
Elongated trapezoidal shape, long straight hinge line with numerous small vertical teeth, strong radial ribs, and the characteristic brownish-white zigzag or banded color pattern.
Collector Value
Low to moderate value. While attractive due to their contrasting patterns, they are common throughout their range and typically valued at a few dollars for standard specimens.
Condition Notes
Fair to Good condition. Shows some natural wear along the margins and minor surface fading, but retains much of its distinctive brown and white color pattern and structural integrity.
Interesting Facts
Unlike most clams that burrow into sediment, Ark shells use tough protein threads called a byssus to anchor themselves permanently to hard surfaces. They have simple eyes along their mantle edge that can detect changes in light and shadow.
Ecological Role
Acts as a filter feeder, helping to clear organic particles from the water column. They also provide habitat and attachment surfaces for various encrusting organisms like algae and sponges.
Similar Species
Bloody Ark (Arca imbricata) and Transverse Ark (Anadara transversa), which can be distinguished by differences in rib count, overall proportions, and geographic distribution.
Beach Finding Tips
Look along rocky shorelines, jetties, and areas with coral rubble after storms, especially at low tide. Single valves wash ashore regularly.