>OF COURSE left handedness is rare. My son is left handed---and he's
>rare. I would imagine that there are sinistral critters most
>everywhere. Left handed Crocodiles, Racoons, Armadillos, Elephants.
>It is not as rare as Albinism---just one of those things that makes
>living things interesting.
>    Now get to the basic question: IS there handedness at all in
>fish, bugs, birds?
>     In shells, it is the shell that is sinistral. How does that
>affect the critter in it?
>    Q Man

Let's see if I can get this on the list...

Sinistral shells don't affect the critter, as the critter MAKES the
shell. A reversed animal will make a reversed shell. So the entire
animal and shell are exact mirror-images of a normal specimen.

Some poor misguided characters believe that the shell twists the
animal... and also that a hyperstrophic dextral shell (Lanistes,
Limacina, protoconchs of pyramidellids, other opisthobranchs and
architectonicids) is sinistral because it LOOKS superficially
sinistral (Planorbidae are sinistral equivalents... though they look
dextral, they are in fact hyperstrophic sinistral). In this case the
animal is uncharacteristic and "puts a new twist on" the shell,
though this has been going on at least since the Devonian. In thse
critters the animal is a normal (usually dextral) but has a
deformity, you could say... the viscera "drops below" the head-foot
instead of standing "above" it (iusing normal orientation eg as used
in photography). This means that instead of coiling toward the
animal's anterior, growth is toward the posterior... so the shell
apex is on the outer lip (labrum) and the apparent "apex" is in fact
the extruded base.

Almost all living gastropods are orthostrophic; they grow from the
apex toward the anterior direction, "dropping downward" along the
coilng axis (geometrically an anteriorward translation). This goes
for both sinistral and dextral species, both normally and abnormally
so. A tiny minority of species today are hyperstrophic, that is, they
translate POSTERIORward; such shells were far more common in the
Ordovician, such as Macluritoidea. No gastropod after the Triassic is
truly isostrophic, that is, coiling in one exact plane, producing a
shell much like that of modern Nautilus (only the problematic
Bellerophontoidea were truly isostrophic).

Let's have another go at explaining this... see if I can confuse you
enough to get you to send me all of your collections free.

To visualize a hyperstrophic shell, think of a pilid (hate to admit
it, but Pilidae has chronologic precedence over Ampullariidae) such
as Ampullaria, say one found introduced in a Florida stream. Now, I
hve never heard of a sinistral pilid... ALL pilid species, no matter
what they look like, are normally dextral.

OK, take a Pila shell that's been softened by soaking in Palmolive
dishwashing detergent (softens your hands while you do dishes). Slip
a thin wire tipped with a drop of superglue up the narrow umbilicus
until it sticks to the underside of the protoconch and sets. Now,
gently pull the wire down along its axis... you'll see the shell's
spire become lower as it's pulled in, and the whorls slip apart a bit
and slide over one another's surfaces... eventually the shell is
broad and almost flat, when the protoconch has been pulled down far
enough to be level with the middle of the aperture; the umbilicus has
had to open up, as th whorls will ot become laterally compressed. The
shell is now close to isostrophic, and can be called Marisa, which is
also found introduced in Florida streams. Marisa's spire is extremely
low, but not quite flat, and the shell can be seen to still be
dextral. Continue to pull on the wire. The spire begins to sink below
the level of the center of the aperture and the shell begins to LOOK
sinistral... keep pulling and th whorkls slide across one another
furthet, closing back up on the UPPER surfaces, producing what LOOKS
like a wide umbilicus as what LOOKS like a spire appears on the
bottom of the shell, where a narow umbilicus was before. Continued
pulling deepens the sunken spire's pseudoumbilicus and the everted
umbilicus below grows into a speeter "spire"... eventualy the shell
comes to look like an upsidedown sinistral pilid. But it is NOT
sinistral... no reversal of direction of coiling rotation has
occurred (DAMN, this would be a lot easier to show and for most to
understand if done in a computer-generated "movie"... do we have any
computer-graphics people on the list??).

Think of the individual whorl as it moves in relation to other
whorls. The parietal shield, at the top of the inner lip, is
originally adpressed to the midpart of the previous whorl. With
increasing depression of the epire the parietal shield slips higher
on the previous whorl, until eventually it is attached to the upper
surface of the previous whorl and forms the side of the
pseudoumbilicus. The base of the lip slides upeward also, until in
the extreme form it is attached to the midlevel of the previous
whorl, coming to look like the parietal shield of a sinistral shell.

Pilids do not have any characters which can give obvious clues to
orientation; no lip sinus, no siphonal canal, no sharp
shoulder-angle, no umbilical cords. However some dextral shells do
occasionally have a hyperstrophic abnormality; this is known in at
least 3 genera of Turbinidae (eg Dinassovica smaragdus of NZ,
Sarmaturbo sarmaticus & "Turbo" natalensis of South Africa) and in
two spp of Heliacus. These shells DO have characters which show the
shell's orientation; they also have colied opercs, and the operc is
not affected by the strophic abnormality, its coiling remains to show
the shells to be dextral (in reversed coiling the operc's coiling is
also reversed; note that pilids do not have coiled opercs, so
hyperstrophic or sinistral specimens could not be differentiated by
the operc). Turbinids generally have a faint anterior canal, and in
the hyperstrophic specimens this can be seen to be distorted and
plastered against the side of the previous whorl. Likewise Heliacus.
The shell's sculpture will also give the orientation away ie position
of certain spiral ribs etc which are specific to certain parts of the
whorl's surface. These abnormal turbinids also tend to be rather
irregular in growth, indicating that something was wrong with the
animal, apart from the change in growth direction.

Note that some groups combine normal orthostrophy with what appears
to be partial hyperstrophy. Many opisthobranchs (Bulla etc) have
spires sunken to produce a pseudoumbilicus as the posterior parts of
the shell grow "upward" while the anterior end grows normally in an
anteriorward diretction.

I tried to work out how a hyperstrophic specimen of a species with
prominent siphonal canal would look. I chose my old favorite Busycon
perversum. What we get is still somewhat tunip-shaped, but
wierdorama. The shoulder inclines "upward" instead of "downward"; the
bodywhorl is rounded, as the peripheral keel is rolled over/inward
toward the sunken apex; the massive spines are also rolled toward the
sunken apical pit (pseudoumbilicus) and surround it. The swollen
ridge around the canal base runs slightly upward, arounf the middle
of the shell or a bit "above"; I can't quite decide what the canal
does...

I have seen a diagram called Strophy.jpg, and have copied this from a
website (Googling for "strophy.jpg" should find the website). It
shows quite well the differences between dextral & sinistral
orthostrophy & hyperstrophy. It also shows heterostrophic protoconchs
(in these shells the early part of the protoconch is hyperstrophic,
reverting to orthostrophic before the adult shell begins to form eg
Odostomia, Architectonica, Amphibola); note that, despite what you
will read everywhere, there is NO SUCH THING as a sinistral
protoconch on a dextral adult shell. This diagram shows a
"hypothetical" sinistral heterostrophic protoconch, claiming that it
is an unknown possibility; this is untrue, as there is ONE known
sinistral heterostrophic species, the ellobiid Blauneria heteroclita.

Let the collections come!................?
--
Andrew Grebneff
Dunedin
New Zealand
Fossil preparator
<[log in to unmask]>
Seashell, Macintosh, VW/Toyota van nut

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