The explanation is very good. I cant it do better.
with best shelling greetings
Helmut

Helmut "Helix" Nisters
private:
Franz-Fischer-Str. 46
A-6020 Innsbruck / Austria / Europe
phone: 0043 / 512 / 57 32 14
e-mail: [log in to unmask]
website: www.netwing.at/nisters
office:
Natural History Department of the
Tiroler Landesmuseum Ferdinandeum Innsbruck
Feldstrasse 11a
A-6020 Innsbruck / Austria / Europe
phone: 0043 / 512 / 58 72 86 - 37
e-mail: [log in to unmask]
website: www.tiroler-landesmuseum.at


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> Hi Harry,
>
> I started typing a response to your question, but what I was typing was
> sounding awfully familiar.  I finally remembered that I had already typed
it
> a couple of years ago, in response to someone else's question, so I went
to
> the Conch-L Archives, found it in about 2 minutes (isn't that search
engine
> GREAT?), touched it up a bit, and am re-posting it here, in response to
your
> question:  A dwarf, as usually defined in conchological circles, is a
specimen
> which is
> (1) a fully mature adult, morphologically representative of the species
AND
> (2) "substantially smaller" in overall dimensions than the low end of the
> "usual" adult size range for the species.  (This is my own definition,
> carefully developed and repeatedly updated over the last two minutes or
so -
> but I think it incorporates the usual thinking among those of a
> conchological bent).  This is a considerably looser definition than that
> employed in mammalian (including human) biology, where dwarfism is a well
> understood genetic condition with well defined parameters. Also, this
> definition necessarily incorporates some rather imprecise terms, since
> molluscan "dwarfism", from the collector/dealer point of view, is defined
> only in terms of size, not underlying causes - and there are no clearcut
> rules or guidelines indicating how small a specimen has to be to qualify
as
> a "dwarf".  I have some Cypraea cervinetta that measure 30-32 mm.  I think
> those qualify as "dwarfs". I also have some of 40-45 mm.  Dwarfs?
Probably.
> How about 50-55 mm? Hmmmm??  Actually, I have seen fully mature Cypraea
> cervinetta in every possible size from 30 mm to over 100 mm.  There is no
> size gap separating "dwarfs" from non-dwarfs, so dwarfs are simply those
> that fall below the line, wherever   you choose to draw it.  That brings
us
> to the other essential criterion - before you can call a specimen a
"dwarf",
> you have to be certain that it is a fully mature, full grown specimen,
> because children are a lot smaller than adults in the mollusk world, just
as
> in the human world.  This is frequently not as easy as it might sound.  I
> tend to think of three general patterns of growth in shelled mollusks.
I'm
> sure there are countless variations within each pattern, but I'm trying to
> keep this simple. Pattern 1 - the lip of the shell is "simple", that is
> smooth and relatively thin, throughout the life of the animal (Naticidae,
> Trochidae, Turbinidae, Ficidae, Bullidae, most Conidae). In some of these
> there is a thickening of the lip edge as the animal matures, in others not
> so.  Pattern 2 - the lip is simple during growth phases, but becomes
greatly
> thickened into a "varix" during non-growth stages (Muricidae, Cymatiidae,
> Cassidae, Tonnidae).  Pattern 3 - the lip is simple throughout the life of
> the animal, until it is fully mature, at which point a one-time
> transformation into an "adult" form occurs, followed by little or no
overall
> increase in size (Cypraeidae and their relatives - Triviidae, Ovulidae;
> Strombidae and their relatives - Aporrhaiidae, Struthiolariidae).  A
> variation of this pattern is species in which the lip is thin until
> maturity, but then becomes greatly thickened, as in Turbinellidae, many
> Volutidae, and some Conidae. Usually, the only species in which "dwarfs"
can
> be reliably identified are those with growth pattern #3.  In these
species,
> a mature specimen is immediately distinguishable from an immature
(subadult,
> juvenile) specimen, irrespective of size.  A 40 mm Strombus raninus with a
> fully developed lip is a mature specimen, and - perhaps? - a dwarf; an 80
mm
> specimen without a mature lip is a juvenile.  In the other two groups,
> dwarfs may exist, but if so, they would look just like the juvenile
> specimens of the species.  No shell dealer would offer a 50 mm Conus
> gloriamaris as a "dwarf".  It would simply be assumed to be a juvenile.
On
> the other hand, a 50 mm Cypraea cervus with mature form and pattern would
> immediately be listed as a dwarf (immediately after attaching a hefty
price
> tag that is!).  Note - this doesn't mean that the 50 mm Conus gloriamaris
is
> not a dwarf!  It just means there is no way of knowing, so we assume the
> most likely explanation to be the correct one.  And, anyone who offers ANY
> non-gastropod mollusk as a "dwarf" is definitely venturing onto thin ice!
> Can you imagine? Dwarf Tridacna gigas - only 300 mm!
>         Paul M.
>