Dear listers,

Andrew gives a good analysis of the hyperstrophic condition.  Consistent
with the telescope analogy, savvy illustrators often figure hyperstrophic
shells with the apex toward the bottom of the page while using the usual
apex-upward pose for the orthostrophic shells (whether sinistral OR
dextral) - that way the aperture of a Lanistes (upside down) is on the
right of the shell, just as it is for the confamilal Pomacea (apple snail)
placed rightside up.

One clue to orthostrophic vs. hyperstrophic coiling is the growth pattern
of the snail's operculum (if present and of spiral configuration).  When
the attached side of the operculum of a "normal" (orthostrophic) dextral
snail is examined, the growth is clockwise, just as the shell, apex toward
the observer, grows clockwise; orthostrophic sinstral shells and opercula
are, likewise, both coiled counterclockwise.

Regrettably, the operculum of our Lanistes grows concentrically rather than
spirally, so the evidence of hyperstrophy in this genus is based on the
organization of the soft anatomy. Paleontologists, who usually lack such
the escargot, have inferred the hyperstrophic (pseudosinistral) condition
of the majority of the Upper Cambrian to Triassic suborder Macluritina Cox
and Knight, 1960 from preserved opercula of certain constituent species.
(I am rather certain this is the large, extinct group to which Andrew refers.)

The condition of a sinistral animal normally making a dextral shell
(hyperstrophic pseudodextral; the exact opposite of the Lanistes topology)
is manifest in the aquatic pulmonate family Planorbidae, most notably,
perhaps, in the genus Carinifex W. G. Binney, 1863, which occurs in the
western U. S.

There is still another layer of complexity in snail-coiling - heterostrophy
- in which the larval and adult shell have different coiling axes.... but
that is another story.

Harry


At 04:06 PM 7/14/99 -0400, you wrote:
>Andrew Vik

>Fellow Conch-lers:
>
>Hyperstrophic coiling is very confusing because most hyperstrophic species
went
>extinct eons ago. Very few books even mention it. Most just show typical
dextral
>and sinistral orthostrophic coiling. The best way to explain
hyperstrophism is
>the telescope analogy. Think of an average dextral shell with the apex
being the
>eyepiece and the aperture being the objective end of the telescope.
Collapses the
>telescope until all the sections are in the same plain; the result is a
>planispiral telescope (like the snail  Marisa cornuarietis). Now, destroy the
>telescope by pulling the eyepiece through the larger objective end. The
result is
>a hyperstrophic and useless telescope. In a hyperstrophic snail, the apex
looks
>like an umbilicus and the umbilicus looks like the spire. There were also
>hyperstrophic snails that coiled sinistrally in ancient times. If we
include the
>extinct Bellerophontacea, which coiled isostophically like the Nautilus, that
>gives us fully five different ways that gastropods have coiled their shells:
>orthostrophic dextral, orthostrophic sinistral, hyperstrophic dextral,
>hyperstrophic sinistral, and isostrophic (which can be neither dextral nor
>sinistral). I hope that I didn't further confuse this matter.
>
>Andrew
>
>Harry G. Lee wrote:
>
>> Dear Manuel,
>>
>> You have convincingly described an (aquatic) Ampulariid snail in the genus
>> Lanistes Montfort, 1810.  As best I can tell the genus is limited to
>> Africa.  The animal is actually dextral, which means the left-handed shell
>> is hyperstrophic pseudosinistral.  Confusing?  Maybe that's why they're
>> (along with confamilal relatives) called mystery snails?
>>
>> Harry
>>
>> At 12:27 AM 7/13/99 +0200, you wrote:
>> >Dear friends:
>> >
>> >        A friend of mine brought me an interesting shell from his trip to
>> >the Okanvango Delta, in Bostwana. It is sinistral, about 45 mm big,
greenish
>> >in colour, and silky in appearance. It was collected inside the water,
so it
>> >seems to be a fresh water species, rather than a land or tree snail. Do
you
>> >know what species is it? I have no experience nor references for this sort
>> >of shells.
>> >        Thank you, and greetings from southern Spain
>> >
>> >                                Manuel Jimenez Tenorio

Harry G. Lee
Suite 500
1801 Barrs St.
Jacksonville, Fl. 32204
USA   904-384-6419
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Visit the Jacksonville Shell Club Home Page at:
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