Diodora aspera 

Common name(s): Keyhole limpet, Rough keyhole limpet, volcano limpet

Phylum Mollusca
 Class Gastropoda
  Order Archaegastropoda
   Suborder Pleurotomariina
    Family Fissurellidae
Diodora aspera at Rosario
(Photo by: Dave Cowles, 1997)
Description: Shell is caplike, like a limpet and up to 7 cm long.  The apex of the shell has a round or broadly oval anal opening which is about 1/10 the length of the shell.  Animal's mantle, when the animal is alive, covers only the very margin of the shell if at all (shell is nearly entirely exposed).  Shell is often gray or gray-brown and sculptured with coarse radial ribs (picture), may have black and white radiating stripes (picture).

How to Distinguish from Similar Species: In Puncturella  and Fissurella species the dorsal hole is an elongated slit. Megathura crenulata (the giant keyhole limpet) lives farther south, grows much larger, and the mantle covers much to all of the shell when the animal is alive.

Geographical Range:  Afognak Island, Alaska to Camalu, Baja California.

Depth Range:  Low intertidal to subtidal

Habitat:  Common in rocky areas all along the coast

Biology/Natural History:  Species is omnivorius but prefers encrusting bryozoans.  Extends its mantle extremely when it encounters a seastar predator (such as Pycnopidia, Leptasterias, Pisaster, or Orthasterias) so that the shell is largely covered and the seastar has no place to grab onto the shell.  Often contains a symbiotic polychaete worm Arctonoe vittata (picture) in its mantle cavity  which may bite the seastar as well.  Diodora's blood contains hemocyanin, has a low pH (7.1) and no Bohr effect.

Return to:
Main Page Alphabetic Index Systematic Index Glossary


Dichotomous Keys:

Kozloff, 1987, 1992
Smith and Carlton, 1975

General References:
Kozloff, 1993
Morris et al., 1980
Niesen, 1994

Scientific Articles:

General Notes and Observations:  Locations, abundances, unusual behaviors, etc.:

View of the underside of the animal showing the foot, head with antennae (left), mantle cavity, and mantle.  Dave Cowles 1997

A specimen in a cave at Cape Flattery, 2004 (Dave Cowles), along with its commensal polychaete flatworm, Arctonoe vittata.  Note ridges and color pattern on shell.

This individual is in the intertidal in Deception Pass.  Photo by Dave Cowles, April 2007

This individual, partly encrusted with bryozoans, was on Swirl Rocks.  Photo by Dave Cowles, July 2007

Flat Diodora aspera
Flat Diodora aspera profile
This Diodora aspera in the two photos above was found at Kalaloch Beach #4 in July 2019. It has an unusually flat shell with a partly concave profile. It appears that the shell is so flat that the animal cannot fit inside its shell and instead extends far below it even when disturbed. What caused it to grow this way is unclear. Photo by Kayla Nash, July 2019

Sponge on Diodora aspera
This keyhole limpet, found intertidally at Cape Flattery, has its shell thickly overgrown by a sponge so the animal cannot be seen at all except from underneath. The limpet's foot and the edge of the shell are exposed on the underside. I did not check to see whether all these holes in the sponge were oscula or whether there was still a passage leading down to the limpet's vent.  If not, how does this limpet excrete wastes? I am not certain whether it has a passageway down to the head region. Photo by Dave Cowles, July 2019

Authors and Editors of Page:
Dave Cowles (2004):  Created original page