Original Message -----
From: David Campbell <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, October 04, 1999 11:52 AM
Subject: Families and Nacreous interiors

> Obviously, the pearl oysters have nacreous shell interiors, including
> Pulvinitidae which has a single living species.  Most nuculids have
> nacreous interiors (except for Condylonucula), as do most
anomalodesmatans,
> including Pholadomya candida, the only living representative of
> Pholadomyidae, and the extinct Margaritaridae, with a single genus.
>
> However, there are lots of things with non-nacreous shell interiors,
> including modern veneroids, caenogastropods, euthyneuran gastropods,
> arcoids, pectinoids, ostreoids, limoids, solemyoids, and nuculanoideans.
>
> David Campbell
>
> "Old Seashells"

Thanks, David.....

Duh!  Obviously.  I was too busy playing to think!  Walter Sage told me that
once, but I'm sure he mentioned the pearl oysters. He thought a lot.

Pulvinitidae is a new one on me!  Another Australian species.  I've just
found a drawing of one in _The Southern Synthesis_ and it is odd!
Foramelina exempla Hedley, 1914 must be the single species of which you
speak.

And I do remember about the nut clams, now that you mention them.

Tom Watters plainly told us that fossils don't count, so the extinct
Margaritaridae are naught but a quibble, right?

However,  I never noticed about the anomalodesmatids.  And I don't know much
about them, and they really look interesting...nacre is thin on them, it
seems...oh well there goes the grocery store trip...throw out the list, and
Richard can eat his cereal without milk....  First thing I found is that
modern thraciids have "an aragonitic, granular homogeneous shell
microstructure, whereas Runnegar found that thraciids from the Mesozoic have
'nacreous'shells"...  Hmmm...bivalves are, in spite of Kevin Lamprell's
efforts, so unsung! I am really glad to have  as a resource this _Southern
Synthesis_, and, of course, you too, David!

One thing about those nacreous interiors I'd like to ask...I was told by our
same Walter Sage a long time ago that a nacreous interior reveals  close
relationship to some very early molluscan forms.  That seems to be true with
the gastropods, with mostly haliotids and slit shells and trochids and
turbos and some patellids etc. having nacre. And the nautiloids are quite
ancient, aren't they? But the bivalves don't seem to bear that out. Nut
clams occur early in the taxonomic scheme, and oysters don't occur so very
long after them maybe,  and the Trigonia and unionids after that. But the
anomalodesmatids are "at the back of the book," so to speak.  Are there, in
fact, any rules of thumb? Is nacre just a convergently evolved character? Or
is there a bunch I am missing? (likely.)  What else is noteworthy about
nacre?  It doesn't seem to hold up as long.  And it does seem to turn dark
with extreme age...I found a fossil pearl at the Sarasota Fossil Pits, and
it is blackened.

And are American jingle shells (Anomia simplex) considered nacreous?  And,
while I am thinking, aren't the Mytilidae nacreous?

Thanks!

Lynn in Louisville, with only soy milk on hand...it'll never pass!
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