>Big Q: How far back can recent families be traced to their origins?

This depends on whether you are interested in the extant family that appeared earliest or the longest continuous sequence, possibly regarded as including multiple paraphyletic families.

Within the Mollusca, good candidates for the oldest recognizable living families are in the protobranch bivalves.  Solemya and Acharax are both credibly reported from the Carboniferous.  Malletids and nuculids also occur quite early.

A good transition sequence from Early Cambrian monoplacophorans such as Watsonella to Early Cambrian bivalves such as Fordilla and Pojetaia suggests that all modern bivalves can be traced back to forms such as these, but this tracing would involve families generally regarded as extinct.  (Certain Russian classifications such as Starobogatov, 1992, have considered extant forms to be close to Fordilla, however.  This does not seem likely.)

>When did the long slender shells(Eps., Ceriths, Augers, etc.) split from some common ancester?

Long slender gastropods appear convergently in several groups.  In fact, some Paleozoic moderately tall-spired forms may not even be true gastropods.  Turbonilla, Epitonium, and Halistylus diverged at least by the Ordovician, though the taller shell did not arise in Halistylus until quite recently.  Eps, ceriths, and augers are all caenogastropods and so have a bit more recent common ancestry.  Relationships within the caenogastropods remain debated, but all three of those probably developed tall shells independently.

>Is a Clade or Tree available?

Lots of them are available.  No one tree is strongly supported as of yet, though some features seem to be generally agreed upon.  DNA studies have a fair amount of potential here, but also as many pitfalls as morphology.  Careful study of exceptionally preserved Mesozoic and Paleozoic gastropods has also helped a lot in sorting out the origins of modern groups.

    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!