Betty Jean wrote:
<Are there such things as dwarfs in the molluscan world, and among
these dwarfs are there both females and males?>
 
Let me address the second question first - I don't know.  If any
research has been done on this, I'd be interested to hear about it.
As for the existence of "dwarfs" in the molluscan world, there
certainly are occasional specimens which qualify as "dwarfs" by
conchological standards.  A dwarf, as usually defined in
conchological circles, is a specimen which is (1) a fully mature
adult 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 physiologic condition with well defined causes.
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 seen a good
number of the little Cypraea cervinetta Betty Jean mentioned.  I have
had some that measured 30-32 mm.  I think those qualify as "dwarfs".
Others were 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).
Pattern 2 - the lip is simple during growth phases, but becomes
greatly thickened into a "varix" during non-growth stages (Muricidae,
Cymatiidae, Harpidae, 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, 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, indicative of the rarity of such a specimen).  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.