Lottia instabilis (Gould, 1846)

Common name(s): Unstable limpet, Unstable seaweed limpet, Rocking chair limpet

Synonyms: Collisella instabilis, Acmaea instabilis
Phylum Mollusca
Class Gastropoda
Subclass Prosobranchia
Order Patellogastropoda
Family Lottiidae
A very large Lottia instabilis found at Hobuck Beach, on the open coast near Neah Bay, WA.  This shell was empty and washed up on the beach.
(Photo by: Dave Cowles, July 2007)
Description:  This limpet is elongated, with the right and left margins of the shell nearly parallel for part of its length.  The anterior and posterior ends are raised so that the limpet fits snugly on a cylindrical surface such as the stipe of an alga but does not lit flat on a flat surface (photo).  Iit rocks on a flat surface, leading to the name instabilis).  Exterior of shell mostly brown with no ridges and a smooth margin; may be lighter near apex.  Apex is slightly in front of center.  Interior bluish-white, frequently with a central brown blotch and a dark margin.   Length to about 3.5 cm.

How to Distinguish from Similar Species:Lottia pelta and Lottia ochracea may live on kelps and be similarly shaped, but Lottia pelta has prominent ribs and Lottia ochracea has a thin, translucent shell with an external checkerboard pattern.

Geographical Range: Kodiak Island, Alaska to San Diego, CA

Depth Range: Intertidal to 73 m

Habitat: On the stipes and holdfasts of kelp

Biology/Natural History: Lives and feeds on kelp stipes and holdfasts, especially on Laminaria setchellii and Pterygophora californica.  In cenral CA it lives only on L. dentigera and L. andersonii. This species runs away quickly if it contacts a seastar such as Pisaster ochraceus.



Dichotomous Keys:
  Flora and Fairbanks, 1966 (as Acmaea instabilis)
  Kozloff 1987, 1996
  Smith and Carlton, 1975

General References:
  Brusca and Brusca, 1978 (as Collisella instabilis)
  Harbo, 1997
  Johnson and Snook, 1955 (As Acmaea instabilis)
  Kozloff, 1993 (As Collisella instabilis)
  McConnaughey and McConnaughey, 1985 (As Collisella instabilis)
  Morris, 1966
  Morris et al., 1980 (as Collisella instabilis)
  Sept, 1999

Scientific Articles:
Phillips, D.W., and P. Castori, 1982.  Defensive responses to predatory seastears by two specialist limpets, Notoacmaea insessa (Hinds) and Collisella instabilis (Gould), associated with marine algae.  J. Exp. Mar. Biol. Ecol. 59: 23-30

Web sites:

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

The uneven edges of the shell of Lottia instabilis can easily be seen in this end and side view.  The shell is shaped to fit snugly around a round stipe instead of a flat surface.

This species is said to have a brown blotch inside its shell but the blotch is not evident in this individual.  The shell was found empty and the
brown blotch may have weathered away.  The anterior end of the shell is to the left.

Authors and Editors of Page:
Dave Cowles (2007):  Created original page
Jonathan Cowles (2007):  Updated page with CSS