Antillean Ark, Wing Ark
Phylum: Mollusca, Class: Bivalvia, Order: Arcida, Family: Arcidae, Genus: Arca, Species: Arca imbricata · Arcidae (Ark shells) · Bivalve (fragment); rectangular/trapezoidal shape with cancellate sculpture
Species
Arca imbricata (Confidence: 85% based on sculpture)
Shell Type
Bivalve (fragment); rectangular/trapezoidal shape with cancellate sculpture
Family
Arcidae (Ark shells)
Size
Approximately 25mm (1 inch) in length. This is a partial specimen; full adults of this species typically range from 25mm to 60mm.
Color & Pattern
Dull chalky white with hints of cream. The fragment appears beach-worn and sun-bleached, losing the typical brown periostracum and streaks naturally found in live specimens.
Rarity
Very Common (especially as fragments or beach-worn valves on Caribbean shores)
Habitat
Attached to rocks, corals, or other hard substrates via a strong byssus. Found in intertidal and shallow subtidal zones up to 50 meters deep.
Geographic Range
Western Atlantic: North Carolina to Brazil, including Bermuda, the Gulf of Mexico, Cancun/Caribbean, and the West Indies.
Description
This is a beach-worn fragment of an Ark shell valve. It exhibits a distinct 'cancellate' or lattice-like sculpture where strong radial ribs are intersected by finer concentric growth lines, creating a beaded or checkered texture. The shell material is thick and sturdy, characteristic of the Arcidae family.
Key Features
Cancellate sculpture (cross-hatched appearance), heavy calcification, and typically a straight hinge line (though the hinge is missing in this fragment). Small pits visible are likely from bioerosion.
Collector Value
Minimal financial value ($0-$1) due to its fragmentary and worn state. It serves as a good 'study piece' for learners identifying Caribbean marine textures.
Condition Notes
Poor to Fair. This is a non-articulated fragment lacking the hinge and umbo. It shows significant rounding from wave action and bleaching from UV exposure. Some minor boring holes from sponges or predatory gastropods are visible.
Interesting Facts
Ark shells are named for their resemblance to Noah's Ark when the two valves are closed. They use a 'byssus' (a tuft of tough fibers) to anchor themselves so firmly to reefs that they are often difficult to pry off without breaking the shell.
Ecological Role
Filter feeder, removing plankton from the water column. When alive, it provides a micro-habitat for encrusting organisms like algae and bryozoans. Currently not a protected species.
Similar Species
Barbatia domingensis (White Reticulated Ark) which is smaller and more oval; Arca zebra (Turkey Wing) which has much larger, bolder brown stripes.
Beach Finding Tips
In Cancun, look in the 'shell hash' lines at low tide. This species is often found near rocky outcroppings or reef breaks where the surf carries broken pieces onto the sand.
Notes
Cancun