Pseudochama exogyra (Conrad, 1837) 

Common name(s): Reversed chama, Jewel box

Phylum Mollusca
 Class Bivalvia
   Subclass Heterodonta
    Order Veneroida
     Family Chamidae
Pseudochama exogyra on rock among coralline algae at Laguna Beach, CA
(Photo by: Dave Cowles May 1998)
Description:  The right valve of this bivalve is larger than the left, and is cemented firmly to the substrate such as a rock.  The right valve forms a "box" while the left valve forms the "lid".  The shell is thick and white.  Shell to about 5 cm diameter.  The beaks coil to the left (counterclockwise) as viewed from above.  May have frills on valves but these are often badly worn or missing.  Exposed mantle and siphons are orange; tentacles are white.

How to Distinguish from Similar Species:Chama arcana is attached by its left valve & has a waxy-translucent exterior.  Its beak coils to the right (clockwise) as viewed from above.

Geographical Range:  Oregon to southern Baja California.  Not likely to be found north of Oregon

Depth Range:  Middle intertidal

Habitat:  On rocky reefs along the outer coast

Biology/Natural History: Often in large clusters on rocks along the outer coast.  Often with Chama arcana and the tube snail Serpulorbis in California.  Valves are thick and dense; apparently lack calcite.  Related to the extinct (Mesozoic) group of rudists.  The shell rotates (clockwise?) while it grows, leading to the spiral lines.

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Dichotomous Keys:
  Allen, 1976
  Kozloff 1987, 1996
  Reish, 1972
  Scott and Blake, 1998
  Smith and Carlton, 1975

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

Scientific Articles:

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

A cluster of Pseudochama exogyra on the rocks among algae.  Note the barnacles on some of the valves.  Photo by Dave Cowles, Laguna Beach, CA 1999

Authors and Editors of Page:
Dave Cowles (2005):  Created original page