>While I generally agree, perfection is pleasing to view.
>My collection would be missing several families.

"Perfect" shells are a tiny minority, despite the claims of dealers.
Esthetically a perfect shell is nicer to look at than an imperfect
one, but we live in the real world (don't we?). As a scientific
collector, I will collect ANYTHING if it's a species I don't already
have, or if it's something very rare; this might be just an apertural
ring, with the rest of the shell missing. Damaged shells can tell a
story... turritellids with crab-peeling scars show just how far the
animal can retract, and how many times this can happen to one snail
(the crabs haven't learned not to bother turritellids since at least
the Oligocene, 25my ago). Other scars can show failed prying by
gastropods, failed naticid/muricid borings... and even sometimes show
that a successful naticid boring was not fatal.

>Sulphur sponges, Cleonia sp. are a major force in the degradation of
>dead shells. They absorb the calcium carbonate for their own
>skeletons, ultimately absorbing the entire shell. A partially
>absorbed shell appears to be as Swiss cheese - totally riddled with
>holes and galleries. Cleonia cannot survive buried in the ocean
>bottom. That part of a shell buried in the bottom  is protected
>from the sponge. If the shell is dislodged from its place in the
>bottom by shifting currents and subsequently washed ashore those
>parts that are partially absorbed break away easily
>(separating along the dotted line comes to mind) leaving the
>unabsorbed portion. That is one way that one finds large gastropods
>beautifully split down the spire revealing the inner spire
>structure. The question is "how can something so fragile get split
>like that without destroying the spire?" This is but one example of
>the effects of Cleonia. I have shells ! missing syphonal canal,
>dorsum, spire only, etc. It depends on what part of the shell was
>buried in the bottom. The clue that a sponge was involved is on the
>break surface with the galleries of holes.

>My interest was piqued by your comments on the boring sponge that
>creates such havoc with shells. I've wondered what the sponge looks
>like. Does Cleonia bore through the shell and also live in the holes
>created? Or is it in the shell interior? Or a mix? Is it microscopic?

>Cliona bores in any calcium carbonate substrate.  A shell with live
>Cliona will have lots of usually yellow dots-the sponge lives in the
>holes that it makes within the shell, not in the space where the
>mollusk is or was.

Cliona (not Cleonia) dissolves passageways and networks between the
inner & outer walls of the shell. The osculae (inhalant openings)
perforate the outer shell surface and appear as 1-2mm yellowish
circular patches. A living shell (eg Fusitriton magellanicus) can be
reduced to a wreck, just an inner surface and a hole-eaten outer
surface joined only at widely-spaced points; the upper spire and
canal may crumble away, as may the lip. But it doesn't harm the
animal itself, unless it's bitten by a fish or attacked by a crab and
the weakened shall fails. I have a few of these sorry Fusitriton in
my collection. They are impressive.

I also have three very thinshelled Oligocene scallops (Janupecten
hochstetteri) with Cliona borings; the shells are translucent, so the
tracery of tunnels is visible. Cliona (or related genera) have been
around for a while.

>The name is unfortunately similar to a few mollusk genera (such as
>Clio) in its stem, affecting the spelling of family names.  I don't
>immediately recall who got to keep the Clionidae and who had to
>change.

Clionidae is in current usage within the pteropods.

Other beasties that bore shells? Phoronids (U-shaped borings with 2
openings), boring (shellless) barnacles, polychaets, bryozoans,
bivalves (especially Gastrochaenidae)... haven't heard of boring
forams yet.
--
Andrew Grebneff
Dunedin
New Zealand
Fossil preparator
Seashell, Macintosh, VW/Toyota van nut
‚ Opinions stated are mine, not those of Otago University
"There is water at the bottom of the ocean"  - Talking Heads

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