Species of bivalve
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Isognomon perna, the brown purse shell or rayed tree oyster, is a bivalve in the family Isognomonidae common in the Indo-Pacific including Hawaii.
Description.
"Isognoma perna" colors range from a brown or light-yellow purse shell to beige with a brown striped pattern and resembles a miniature clam.
Distribution.
Commonly found in the Indo-Pacific, including Hawaii, Western Polynesia, Eastern Polynesia, North to Japan Eastern to Southern Africa, New Caledonia, and Society Islands. 
Habitat.
"Isognomon perna" live at depths of 0-20m in tropical climates; byssally attach to rocks, reef flats, or the underside of boulders. Commonly found under rocks in shallow water and arranged one on top of the other.
References.
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