Cayenne Keyhole Limpet
Phylum: Mollusca, Class: Gastropoda, Order: Lepetellida, Family: Fissurellidae, Genus: Diodora, Species: Diodora cayenensis · Fissurellidae (Keyhole Limpet family) · Gastropod (Univalve); Cap-shaped/Conical shell with an apical perforation.
Species
Diodora cayenensis
Shell Type
Gastropod (Univalve); Cap-shaped/Conical shell with an apical perforation.
Family
Fissurellidae (Keyhole Limpet family)
Size
Approximately 0.75 inches (19mm). This is a typical adult size; the species usually ranges from 0.5 to 1.5 inches in length.
Color & Pattern
Overall grayish-tan to pinkish-brown with darker radiating bands. The surface features approximately 30-40 radiating ribs, every fourth rib being noticeably stronger, creating a latticed or beaded appearance. The apex 'keyhole' hole is outlined in a darker pigment.
Rarity
Common; frequently found on North Carolina beaches, especially near rocky inlets or jetties.
Habitat
Marine; intertidal and shallow subtidal zones. They are typically found clinging to rocks, shells, or pilings in high-energy areas like jetties and reefs.
Geographic Range
Western Atlantic: New Jersey south to Florida, Gulf of Mexico, Caribbean, and Brazil. Common along the North Carolina coast including Holden Beach.
Description
A sturdy, conical shell resembling a volcanic peak. The most striking feature is the small, keyhole-shaped opening at the summit (apex). The exterior is heavily sculpted with fine radiating ribs and concentric growth lines that create a rough, decussated (criss-cross) texture. The base is oval and the interior is typically smooth and white.
Key Features
The distinctive 'keyhole' opening at the apex; the orifice is slightly anterior to the center. Strong radial ribs with a beaded texture. Internal callus around the hole is truncated (flat) on the posterior side.
Collector Value
Low; widely available and common for beginners. Its value lies in its interesting morphology. Exceptional large specimens or those with vivid purple banding may hold more interest for specialized collectors ($1-$5 range).
Condition Notes
The specimen appears to be in Good to Fine condition. It retains its natural brownish pigment and sharp radial ribbing. There is slight erosion at the very edges, typical for a beach-worn specimen found in the surf.
Interesting Facts
Unlike many snails, limpets use their muscular foot to create a powerful suction to rocks. The 'keyhole' at the top serves an excretory function; water is drawn in under the edge of the shell, passes over the gills, and exits through the hole, carrying waste and carbon dioxide away.
Ecological Role
Primary consumer; they are herbivorous grazers that use a radula (toothed tongue) to scrape algae and microscopic organisms off rocks and other hard substrates.
Similar Species
Diodora listeri (Lister's Keyhole Limpet) which is larger with coarser ribbing, and Lucapina sowerbii (Fleshy Limpet) which has a larger hole and different ribbing pattern.
Beach Finding Tips
Look in the 'shell hash' piles at the high tide line, especially near the West End of Holden Beach or near the Lockwood Folly Inlet rocks. They are often overlooked due to their small size and camouflaging brown color.
Notes
Holden Beach, NC