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.