>I am doing research for a television show called "MDs,"
>and would appreciate any assistance the members of this
>list could give me.
>
>Do the shells of conches typically grow in one
>particular direction? In other words, does almost every
>conch shell of a certain species swirl rightward, and
>have a right-opening aperture? Is there a clinical or
>taxonomic term for those anomalous shells that grow in a
>direction that is not typical for their species?
>
>Thanks very much.
>
>-Craig Sweeny

What you are referring to is what in amateur parlance is called
"righthandedness" and "lefthandedness". An gross oversimplification
is that most shells, including normal conchs, held with the apex (tip
of spire, most often pointed) held upward will have the aperture on
your right; this is a dextral or "righthanded" specimen. Rare
abnormal conch specimens coil backward, with the aperture on the left
and are sinistral or "lefthanded". Viewed from the posterior end ie
looking at the point of the apex, a dextral shell will spiral in a
clockwise direction toward the aperture. a sinistral specimen will
coil anticlockwise.

Handedness is often (even by the great authorities) misunderstood;
even Abbott wasn't clear on this. A shell which APPEARS to be dextral
or sinistral isn't necessarily so. All definite gastropods apart from
the the Paleozoic isostrophic bellerophontids (many of which may not
be gastropods at all, but monoplacophorans) do not coil in a true
logarithmic spiral, but add another dimenaion by translating the coil
along the coiling axis. The great majority of living or even fossil
species translate "downward" or "forward" along tha axis, producing a
spire at the posterior end and the base, often with a siphinal canal,
at the anterior. Dextrality or sinistrality is easy to define with
shells coiling this way, and such shells are orthostrophic.

HOWEVER some gastropods translate UPWARD or POSTERIORWARD as they
grow; these are termed hyperstrophic. All normally-hyperstrophic
shells lack a siphonal canal, so there is no obvious giveaway sign of
their strophism. However abnormal hyperstrophic Turbo and Heliacus do
occur, and these have an apertural "spout" or umbilical cord, which
in abnormal specimens will be in an odd place. A specimen with a
canal would be glaringly obvious and look really wierd, and I have
never heard of such a specimen. The canal would be wrapped around the
bodywhorl instead of being at the anterior end.

A hyperstrophic-dextral shell will appear sinistral; a sinistral
specimen will appear dextral.

Some normally-hyperstrophic taxa:
Macluritoidea-dextral
Lanistes-dextral
Limacina-dextral
Planorbidae-sinistral

In hyperstrophid corms what appeare to be the apex is in fact an
everted (inside-out) umbilicus. The base in these shells abuts this
pseudospire. Correct orientation of such shells for illustration is
with the pseudospire DOWN, pseudoumbilicus (if present) UP. So the
shell APPEARS to be upsidedown.

Some taxa combine both strophies. Pyramidellidae do NOT have
sinistral protoconchs; the entire shell is of course dextral. However
the early whorls are hyperstrophic; at the beginning of the
teleoconch coiling reverts to orthostrophy. "Bubble" shells do this
also, as do the pseudopulmonate Archaeopulmonata (Amhipbolidae,
Siphonariidae, Ellobiidae) and Mathildidae and Architectonicidae.
Limacinidae (family of small coiled pteropods) are effectively
neotenous, adults retarded at the veliger stage, and so remain
hyperstrophic. Rare abnormal Heliacus (Architectonicidae) fail to
change over and retain hyperstrophy into adulthood. I have no idea
why Turbo smaragda should show hyperstrophic abnormality, but rare
specimens do occur... when I found a live one I was delighted,
thinking it sinistral (and I have seen or heard of other specimens...
have images if anyone wants to see a couple... put HYPERSTROPHIC
TURBO in your subject line so I won't miss it)... but the operculum
gave it away as a dextral shell.
--
Andrew Grebneff
165 Evans St, Dunedin 9001, New Zealand
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Seashell, Macintosh, VW/Toyota van nut