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Keys to the Shells of Bahia la Choya, Sonora, Mexico

  • Nancy Beckvar (a1), Richard D. Norris (a1) and Sherman Suter (a2)


These keys are intended for use on dead shell material found on the sand flat, spit and estero of Bahia la Choya. They describe one hundred seventy molluscan species, three irregular echinoids and an inarticulate brachiopod. The taxonomic list on which the keys are based was compiled from shell material collected mainly during February and March, 1985. An attempt was made to make the keys as complete as possible. However, due to seasonal variations in shell abundances, not all shell material found at Bahia la Choya may be included in the key. Additionally, not all taxa found in the Pleistocene rock exposed around the bay are described here.

The keys are based on morphological similarites, not phylogenetic relationships. Descriptive terminology has been kept to a minimum, and a glossary and labeled sketches are included for those technical terms which were employed. The reader is advised to become familiar with the anatomical parts of shells before embarking on an identification.

External shell morphology can be altered by physical and biological destruction. In particular, fragile shell structures may be broken off, and shell sculpturing may be worn down. The absence of these sometimes critical features may lead to an incorrect identification. Additionally, bleaching of shells can alter or destroy the original colors. Therefore, shell color is not necessarily diagnostic and is mainly used as an additional character in the description of the species.

Species are described only within the keys. When the species name has been reached, phrases within the couplet contain additional descriptive information and often some ecological information.



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Brusca, R.L., ed. 1980. Common Intertidal Invertebrates of the Gulf of California. 2nd Edition. University of Arizona Press, Tucson, Arizona: 513 p.
Keen, A.M. 1971. Seashells of Tropical West America. 2nd Edition. Stanford University Press, Stanford, California: 1064p.
Keen, A.M., and Coan, E. 1974. Marine Molluscan Genera of Western North America: An Illustrated Key. Stanford University Press, Stanford, California: 208 p.
Keen, A.M., and Coan, E. 1975. “Sea Shells of Tropical West America”: additions and corrections to 1975. Western Society of Malacologists. Occasional Paper 1. 66 p.
Morris, R.H., Abbott, D.P., and Haderlie, E.C., eds. 1980. Intertidal Invertebrates of California. Stanford University Press, Stanford, California: 690 p.
Olsson, A.A. 1961. Mollusks of the tropical eastern Pacific, particularly from the southern half of the Panamic-Pacific faunal province (Panama to Peru). Panamic-Pacific Pelecypoda. Paleontological Research Institution, Ithaca, New York: 574 p.


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