>        <In fact, some Paleozoic moderately tall-spired forms may not even
>be true gastropods.>
>        If they were not true gastropods, what were they?  What did gastropods arise from?

The class Paragastropoda has been proposed for apparently untorted Paleozoic mollusks with gastropod-like shells.  It may be a polyphyletic assemblage and not a natural group, however.  Some of the hyperstrophic taxa are thought to not be true gastropods, but the strongest evidence comes from functional studies.  Torsion rearranges the position of the shell relative to the foot.  A tall-spired shell ought to be reasonably aligned with the foot so as to be easy to haul along.  The configuration of the aperture suggests how the shell sat on the animal.  Another approach that has been used is to see how water flow around a shell model match up with inhalant and exhalant currents for torted or untorted shells.  This approach is particularly suitable for apparently sessile forms like macluritids.  I think the macluritids turn out to be highly probably torted, but do not have the references handy.

Gastropods are thought to arise from monoplacophorans s.l.  The paragastropods maybe close relatives of true gastropods, but I do not know of a specific study.

Although St. Mary's has some shell-related advantages over Chapel Hill, such as being closer to the ocean and to fossil mollusks, the primary reason for moving was the opportunity to change from unpaid graduate student to paid professor.

    Dr. David Campbell
    "Old Seashells"
    Biology Department
    Saint Mary's College of Maryland
    18952 E. Fisher Road
    St. Mary's City, MD  20686-3001 USA
    [log in to unmask], 301 862-0372 Fax: 301 862-0996
"Mollusks murmured 'Morning!'.  And salmon chanted 'Evening!'."-Frank Muir, Oh My Word!