By counting the number of whorls on 'normal' sized specimens you can get
an idea of what to expect.  A small specimen with one whorl less is
simply submature, not otherwise unusual.  There still is a wide range of
normal size,  so this is just another datum to take into account.  Note
that some species just keep on growing as they age (adding whorls, of
course).
Allen Aigen  [log in to unmask]

On Sun, 31 Dec 2000 15:24:49 -0500 "Monfils, Paul"
<[log in to unmask]> writes:
> 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.