Pacific Keyhole Limpet
Phylum: Mollusca, Class: Gastropoda, Order: Lepetellida, Family: Fissurellidae, Genus: Megathura, Species: Megathura crenulata · Fissurellidae (Keyhole limpet family) · Gastropod univalve with a conical, cap-like shape and a distinct apical opening (keyhole), whole shell
Species
Megathura crenulata
Shell Type
Gastropod univalve with a conical, cap-like shape and a distinct apical opening (keyhole), whole shell
Family
Fissurellidae (Keyhole limpet family)
Size
Approximately 1 inch in diameter based on visual scale, which is characteristic of a juvenile or small specimen. Adults can typically grow much larger, ranging from 3 to 5 inches.
Color & Pattern
Base color of off-white to cream, accented with characteristic brown to black radial streaks and mottling radiating from the apex. The interior is glossy and white with a dark border around the central keyhole.
Rarity
Common
Habitat
Found primarily in rocky intertidal and shallow subtidal zones down to depths of about 40 meters, adhering firmly to hard rock surfaces and boulders in areas with moderate wave action.
Geographic Range
Eastern Pacific Ocean, ranging from Monterey Bay, California, south to Baja California, Mexico, including San Diego.
Description
A charming and distinctive cap-shaped shell featuring strong radial ribs and a prominent central aperture at the apex, resembling a keyhole. The margin is scalloped and crenulated, giving it a rugged yet symmetrical appearance.
Key Features
Presence of a distinct apical opening (the keyhole) at the top of the shell, strong radial ribs, and a crenulated outer margin.
Collector Value
Low to moderate commercial value, but highly desirable for regional shell collections representing the Pacific coast of North America. Specimens generally sell for a few dollars.
Condition Notes
Good condition with natural coloration intact, minor wear on the ribs, and clear central aperture. No major fractures or boring holes observed. Grade: Good.
Interesting Facts
Keyhole limpets produce a unique cyan-blue defensive protein called keyhole limpet hemocyanin (KLH), which is widely harvested for its biomedical applications in immunology and cancer research.
Ecological Role
Acts as an herbivorous grazer scraping microalgae and encrusting organisms off rocks, helping to maintain the balance of rocky intertidal ecosystems. Prey for sea stars, octopuses, and large fish.
Similar Species
Diodora aspera (Rough Keyhole Limpet), which is typically smaller, taller, and features a different internal callus structure around the keyhole.
Beach Finding Tips
Look along rocky shores and tide pools in Southern California during extreme low tides, especially after winter storms that dislodge shells from subtidal rocks.
Notes
San Diego