Antillean Keyhole Limpet (also known as the Star Limpet)
Phylum: Mollusca, Class: Gastropoda, Order: Lepetellida, Family: Fissurellidae, Genus: Diodora, Species: D. cayenensis · Fissurellidae (Keyhole Limpet family) · Gastropod; specifically a patelliform (limpet-shaped) univalve. Whole shell with characteristic apical pore.
Species
Diodora cayenensis
Shell Type
Gastropod; specifically a patelliform (limpet-shaped) univalve. Whole shell with characteristic apical pore.
Family
Fissurellidae (Keyhole Limpet family)
Size
Approximately 12-15mm (0.5 inches) in length. This is a small specimen; adults of this species typically range from 15mm to 35mm.
Color & Pattern
Pure white to creamy white base. While many living specimens have brown or grey rays, this beach-found specimen appears naturally bleached or is a light color variant. The interior is generally white with a dull to pearly luster.
Rarity
Common; frequently found on Caribbean and Gulf beaches, though small specimens require keen eyesight to spot among shell grit.
Habitat
Intertidal and shallow subtidal zones. Prefers rocky substrates, coral reefs, and jetties where it can cling tightly to surfaces to resist wave action. Marine environment.
Geographic Range
Common in the Western Atlantic, ranging from New Jersey south to Brazil, including the Gulf of Mexico, Caribbean Sea, and the Yucatan Peninsula (Cancun).
Description
A small, conical, shield-shaped shell characterized by a high apex featuring a distinct keyhole-like opening (foramen) just off-center. The exterior is beautifully sculpted with strong radiating ribs of varying thicknesses, intersected by finer concentric growth lines, creating a slightly beady or latticed appearance. The margin is finely crenulated (scalloped).
Key Features
The key diagnostic feature is the keyhole opening at the top, which in the genus Diodora is shaped like a 'squashed' oval or figure-eight and is bordered internally by a heavy, truncated callus. The distinct star-like radiating ribs also characterize this species.
Collector Value
Minimal monetary value ($1-$5) due to its abundance, but highly desirable for aesthetic collections and educational 'starter' sets focused on Caribbean micro-shells.
Condition Notes
Fair to Good. The shell is intact with a well-defined apical pore and crisp ribbing. However, the stark white color suggests it has been sun-bleached on the beach for some time, as it lacks the dark radial stripes often seen in fresh specimens. Grade: Fine.
Interesting Facts
The 'keyhole' at the top of the shell is used for sanitation; waste products and water used for breathing are expelled through this hole. Unlike many snails, they cannot retreat into a whorled shell; instead, they use a powerful muscular foot to create a vacuum seal against rocks.
Ecological Role
Herbivorous grazer; they use a radula (toothed tongue) to scrape algae and diatoms off rocks. They serve as a food source for shorebirds and predatory sea snails. Conservation status: Least Concern.
Similar Species
Lucapina sowerbii (Fleshy Keyhole Limpet) which has a larger opening and more elongated shape, and Fissurella barbadensis (Barbados Keyhole Limpet) which lacks the internal callus plate behind the hole.
Beach Finding Tips
Look in the 'wrack line' or amongst piles of small shell fragments (grit) on rocky beaches after high tide. Because they are tiny and white, they often blend in with broken quartz or coral bits.
Notes
Cancun