Acmaea mitra  White-Cap Limpet, Dunce-cap limpet, Bishop's cap limpet, Chinese hat limpet
Synonyms: none
Phylum Mollusca   Class Gastropoda   Subclass Prosobranchia    Order Patellogastropoda     Family Acmaeidae
	Acmaea mitra shell found at Rosario.  The true shell color (white) shows through, and the shell of this individual is partly eroded by a burrowing species.
	Photo by: Ryan Lunsford 2002

How to Distinguish from Similar Species:  Acmaea mitra is the only all white limpet, and is much taller and conical like a miter or short dunce's cap than are other limpets.
 

Geographical Range:  Aleutian Islands, Alaska to Baja California.

Depth Range:  Low intertidal and mostly shallow subtidal

Habitat:  A. mitra can be found whereever red coralline algae is present.

Biology/Natural History:  Acmaea mitra is known by its tall shell, which can reach a height of 30 mm and a length of 35 mm.  The scientific name means "pointed cap".  This species eats coralline aglae using its radula.  The teeth of its radula are unique amoung marine invertebrates, as they are capped with goethite, and also with silica (opal).  Goethite is an iron compound that forms a hard crystalline cap around the teeth.  A. mitra is also fairly unique amoung limpets as it does not appear to have any defense response system to predators.  Predators include the seastar Orthasterias koehleri and birds such as black oystercatchers and white-winged scoters.

References:
Dichotomous Keys:

General References:
Brusca and Brusca, 1978
Harbo, 1997
Harbo, 1999
Kozloff, 1993
McConnaughey and McConnaughey, 1986
Morris et al., 1980.
Niesen, 1994
Niesen, 1997
O'Clair and O'Clair, 1998
Ricketts et al., 1985

Scientific Articles:

This individual is crawling on a Nucella lamellosa shell.  It is covered with coralline algae, which is usually pink.  The white color suggests that the coralline algae is dead on this individual.
Photo by Dave Cowles, July 2005

The head, tentacles, and foot of this species are white.  Photo by Dave Cowles, July 2010

An underwater photo of Acmaea mitra by Kirt Onthank, July 2007.  The limpet is encrusted with algae.
The two snails in the background are Calliostoma ligatum.

Another individual, photographed in the intertidal.  The limpet grazes on coralline algae, but some coralline algae also often overgrow the limpet's shell.  I do not know whether the algal overgrowth comes due to the fact that the limpet often rests within the algal colony or whether the algae spores or gametes settle anew on the shell.  I rarely see anything else but coralline algae growing on the shell, so that may imply that the overgrowth comes from resting within the algal colony.  Note that many of the coralline algae encrusting the rock already seem to have been grazed in this photo.  Photo by Dave Cowles, July 2010.