Antiguan Arc, White Miniature Arc
Phylum: Mollusca, Class: Bivalvia, Order: Arcida, Family: Arcidae, Genus: Barbatia, Species: Barbatia domingensis · Arcidae (Arc Shell family or Ark Clams) · Bivalve (Two-shelled); specifically one valve (half) of a fan/almond shaped shell with a straight hinge line.
Species
Barbatia domingensis, confidence level 92%
Shell Type
Bivalve (Two-shelled); specifically one valve (half) of a fan/almond shaped shell with a straight hinge line.
Family
Arcidae (Arc Shell family or Ark Clams)
Size
Approximately 1.5 cm (0.6 inches). This is a mature specimen; typical adult range is 1 cm to 2.5 cm.
Color & Pattern
Uniformly chalky white to creamy off-white. The shell appears naturally white, lacking the dark hairy periostracum (outer skin) usually found in living specimens, which likely wore off in the surf.
Rarity
Common; frequently found on Caribbean beaches, though their small size often makes them overlooked by casual beachcombers.
Habitat
Shallow tropical waters, typically found attached to the underside of rocks or within coral crevices in intertidal and subtidal zones.
Geographic Range
Western Atlantic; ranging from North Carolina and Bermuda, through the Florida Keys and Caribbean (including Cancun/Yucatan), down to Brazil.
Description
A small, sturdy, somewhat rectangular to almond-shaped bivalve. The exterior is characterized by a 'decussate' sculpture—a cross-hatched pattern formed by fine radial ribs intersecting with concentric growth lines. The umbo (beak) is positioned toward the anterior end.
Key Features
Distinctive cancellate (checkered) surface texture; a nearly straight hinge line typical of Arks; fine beaded appearance where the ribs and growth lines cross.
Collector Value
Low monetary value ($1-$3), but high interest for 'minis' collectors or those documenting Caribbean biodiversity. Value increases for matched pairs in 'Gem' condition with periostracum intact.
Condition Notes
Good condition. The valve is intact with no major chips. The sculptural details are crisp and not heavily water-worn. The lack of periostracum is expected for beach-collected specimens. Grade: Fine.
Interesting Facts
The genus name 'Barbatia' is derived from the Latin word for 'bearded,' referring to the thick, hair-like coating (periostracum) the living animal possesses to help camouflage it against rocks.
Ecological Role
As a suspension feeder, it filters plankton from the water column. It provides micro-habitats for other small organisms and serves as a prey item for drilling gastropods and crabs.
Similar Species
Acar domingensis (often used synonymously but slightly different sculpture) and Barbatia candida (White Bearded Ark), which grows much larger and has a more elongated shape.
Beach Finding Tips
In Cancun, look in the 'shell hash' lines at low tide. Sift through piles of smaller fragments near rocky outcroppings or jetty areas where small bivalves get trapped.
Notes
Cancun