Physical Description

  • A large gray oblong, oval shell with a single black central hole at the top of the shell, the portal through which waste products are released.
  • Gray, black, or brown slimy mantle (body wall) covering the shell, unlike any other limpet that has mantle under the shell.
  • Adult shell is 3-5 inches in diameter.
  • Sessile animal, permanently attached to rocks.


  • Monterey, California to Baja California, Mexico.


  • Live in the intertidal zone.
  • Found at depths up to 108 feet.


  • Reproduce by broadcast spawning.
  • Embryos develop into planktonic larvae and then juvenile veligers (tiny larvae with cilia to move in water) before settling somewhere permanently and growing into adult form.


  • Filamentous cyanobacteria, diatoms, brown and red algae such as seaweed, seagrass, foraminifera, hydrozoans, bryozoans, nematodes, bivalves, gastropods, crustaceans, and tunicates.


  • People use this species for medicinal uses.
  • The primary predators for limpets are sea stars, birds, and the occasional crab.

Interesting Facts

  • This species is one of the largest keyhole limpets.
  • The whole on the top of the shell makes them different from true limpets, which release waste from the mantle beneath the shell. 
  • The blood of this species is used in many cancer treatments and vaccines, as it stimulates the immune system and its protein transports molecules throughout the body.  
  • A liter of blood from a keyhole limpet will produce 20 grams of protein, which can be worth as much as $100,000.
  • Their shells were used as currency among Native Americans.

Sources: Harris and Markl, 1999; Harvesting blood from limpets for a cancer vaccine; How mollusk blood could cure cancer; Marine Biology. 8th ed.; Encyclopedia of Life;; sealifebase

Photo: Frederic Pache