Crossed Tuft or Reticulated Nut Shell
Phylum Mollusca, Class Bivalvia, Order Arcida, Family Arcidae, Genus Arca, Species Arca imbricata · Arcidae (Ark shell family) · Bivalve (two-shelled), whole shell, trapezoidal to oblong shape with a straight hinge line.
Species
Arca imbricata
Shell Type
Bivalve (two-shelled), whole shell, trapezoidal to oblong shape with a straight hinge line.
Family
Arcidae (Ark shell family)
Size
Approximately 0.75 to 1 inch, which is average for this juvenile or smaller-sized specimen. Adults typically range from 1 to 2 inches.
Color & Pattern
Off-white to cream base color with subtle brownish or reddish-brown patches. The colors appear somewhat faded and sun-bleached due to beach tumbling.
Rarity
Common
Habitat
Found in marine environments, typically attached by strong byssus threads to hard substrates such as rocks, coral reefs, and jetties in the shallow subtidal to intertidal zones.
Geographic Range
Western Atlantic from North Carolina through the Caribbean, the Gulf of Mexico, and down to Brazil.
Description
A sturdy, compact bivalve featuring strong radial ribs crossed by fine concentric growth lines, creating a checkered or reticulated texture. It has an elongated, straight hinge line with numerous small teeth.
Key Features
Straight hinge line spanning the entire length of the dorsal margin, strong radial ribs, and a distinct central gape where the byssus emerges.
Collector Value
Low to moderate. These are common beach finds and generally have little commercial monetary value, though they are great additions to a representative bivalve collection.
Condition Notes
Fair to Good condition. The shell is intact with some minor wear on the margins, moderate sun bleaching, and a smooth texture from wave action. Collectibility grade is Good.
Interesting Facts
Ark shells are unique because they possess true red blood containing hemoglobin, unlike most other mollusks which have clear or blue blood.
Ecological Role
Ark shells act as filter feeders, helping to maintain water clarity, and serve as an important food source for marine predators such as whelks, rays, and large fish.
Similar Species
Other ark shells such as the Zebra Ark (Noetia ponderosa) or Turkey Wing (Arca zebra). They can be distinguished by specific hinge teeth arrangements and overall shell proportions.
Beach Finding Tips
Look along high-tide lines on rocky or shell-rich beaches, particularly after storms in the Caribbean or Southern United States.