Sunday, April 5, 2009

Gastropod shells from the Estero San José beach

The Estero San José and the Sea of Cortez are in some places separated by only a thin bar of sand. One can find shells on both sides of the sand bar. At one of the last winter days, this hand full of mollusk shells was taken from the many shells laying all the way along the lagoon next to the water line. The elongated spires of the shell sculpture show both spiral and axial lines. All shells were found to be dextral: when facing the observer, they have their aperture (the opening through which the mollusk's foot and head protrudes in living animals) on the right side of the axis around which the spiral lines are winding anti-clockwise towards the apex.
Since the lagoon receives freshwater from the Rio San José, the shells should belong to some gastropod species that do well in a habitat with fresh or less salty water. I wonder how much salt water they can tolerate after big waves will have flooded the lagoon with a large amount of sea water?

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