Harry,
  There is a wonderful study of ecotypes by Lois Schoonover (A
Stratigraphic Study of the Mollusks of the Calvert and Choptank Formations
of Southern Maryland. Bulletins of American Paleontology Vol. 25 No. 94B,
1941) which shows how ecotypes can be described as different species. In
1904, the Maryland Geological Society published the Miocene Text and
Miocene Plates, a massive tome covering the Miocene fossils of the
Chesapeake Group found along the Chesapeake Bay in Maryland. In this book,
quite a number of taxa were dealt with.
  Schoonover, for her doctoral dissertation, collected from many sites
along the Calvert and Choptank Formations. Schoonover discovered that some
taxa that were described from the northern and southern ends as different
species were actually the same species. When adequate samples were
analyzed from sites along the length of the formations, the taxa graded
into one another. She found this phenomenon occurred in a number of taxa.
  Being an estuary, the salinity changes from the mouth and decreases as
one heads north. It is quite likely that the change in salinity accounts
for the ecomorphs. In the case of Argopecten gibbus, it might be a
temperature gradient that accounts for the differences that you notice.
Whether one wants to call the differences ecomorphs or elevate them to
subspecies status is another question.


Regards,
Charlie
******************************************************************************
Charlie Sturm, Jr
Research Associate - Section of Mollusks
                     Carnegie Museum of Natural History
                     Pittsburgh, PA, USA

Assistant Professor - Family Medicine

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