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 dorsal shell fragment with a central apical perforation.
Species
Diodora cayenensis
Shell Type
Gastropod (Univalve); Cap-shaped/Conical dorsal shell fragment with a central apical perforation.
Family
Fissurellidae (Keyhole Limpet family)
Size
Approximately 12-15mm (0.5 inches). This is a juvenile or smaller specimen; adults typically reach 25-50mm (1-2 inches).
Color & Pattern
Off-white to creamy white base. It features radial ribbing and faint concentric growth lines. The specimen appears slightly sun-bleached, though this species is naturally pale with occasional grey or brown streaks.
Rarity
Common; frequently found by beachcombers in the Yucatan region and along the Florida coastline after high tides.
Habitat
Found in marine environments, specifically the intertidal and shallow subtidal zones. They adhere to hard substrates like rocks, coral rubble, and jetty stones.
Geographic Range
Western Atlantic, ranging from New Jersey south to Brazil, including the Gulf of Mexico, Caribbean Sea, and the coastal waters of Cancun, Mexico.
Description
A small, sturdy, cone-shaped shell characterized by a distinct 'keyhole' opening at the apex. The exterior is sculpted with numerous fine radial ribs that intersect with concentric ridges, creating a slightly cancellated or beaded texture. The margin is finely crenulated (scalloped).
Key Features
The key diagnostic feature is the keyhole-shaped orifice at the top of the shell, which is used for the expulsion of water and waste. Unlike 'true' limpets, this aperture is located slightly toward the anterior end of the shell's peak.
Collector Value
Minimal monetary value (usually <$1 USD) due to how common they are, but highly desirable for 'miniature' shell enthusiasts and hobbyists due to their unique geometry.
Condition Notes
The shell is in 'Good' to 'Fine' condition. It is largely intact with a clean apical pore, though its white coloration suggests it has been exposed to the sun or surf for some time, losing any darker pigment it may have had in life.
Interesting Facts
The 'keyhole' serves a respiratory and excretory function. In the living animal, the mantle (the tissue that builds the shell) often extends up through and covers part of the shell. They are slow-moving herbivores that graze on algae and sponges.
Ecological Role
They are primary consumers that help control algal growth on reefs and rocky shorelines. They are prey for crabs, sea stars, and certain species of predatory snails.
Similar Species
Lucapina sowerbii (Flesh-colored Limpet), which is more elongated, and Fissurella barbadensis (Barbados Keyhole Limpet), which typically has bolder, darker radiating stripes and a different pore shape.
Beach Finding Tips
Look in 'shell hash' piles at the high tide line. Because they are small and light, they often get caught in seafoam or trapped inside the cavities of larger rocks and sponges washed ashore.
Notes
Cancun