At the risk of getting into something which I am ill-qualified to
discuss, I think the student's observation was that limpets were MORE
conical, rather than less conical in the high-energy zone (rocks at high
tide level).  This was opposite to what the students expected, probably
based on the reasoning you cite.
I am guessing that all limpets, conical or flat are fairly resistant to
wave action since they are all more or less small and round and have
exceedingly strong muscles - even the conical ones have more than
sufficient mechanical strength (guessing again here). Possibly flatness
is more of an advantage from a predation point of view, less able to be
pried off by a beak or a claw, although all limpets are pretty darn
tough to dislodge.
The limpets (Colisella pelta ?) that I observed just a few days ago
right at the extreme high tide line (almost at the level of the road)
were nearly as high as they were wide and half as high as long.
So why are the conical ones higher on the rocks?  The danger from
overheating might be more of a risk than the danger of being pried off.
Just my guess.

A Menez wrote:

> Hi
>
> The classic ecological explanation here is that a more conical shell
> presents a larger surface area on which the energy derived from wave
> action can act. Thus, in more sheltered (i.e. less exposed) situations
> you find more conical forms, in more exposed situations you find the
> more flattened forms. These latter are much more resistant to
> dislodgment by wave action. The best example I can think of off the
> top of my head is the distribution of Patella caerulea on the
> intertidal. In the less-exposed, low energy impact zones you find the
> classic P. caerulea. In the more-exposed, high energy impact zones you
> find the much more flattened form P. caerulea var. subplana. Other,
> similar examples exist for other conical species (e.g. barnacles). I
> am afraid that our old friend natural selection is (fit and) well
> amongst the cones. Progeny of the more flattened species, or varieties
> of species, will be fitter (in the strict sense) than their taller
> cousins in more exposed situations and will prosper there.
>
> (This is NOT meant to spur another evolutionary discussion).
>
> Alex
>
> NORA BRYAN wrote:
>
>> Hi all limpet lovers,
>> This is a very technical question (why and how limpets are more
>> conical at
>> the higher-energy swash zone than lower on the beach).  I couldn't
>> even begin
>> to say how but I have heard that it is advantageous to limpets to be
>> more
>> conical where they are more exposed to protect them from temperature
>>
>> extremes.  The idea is that the water in the apex of the shell
>> provides a
>> measure of protection against overheating, and against cooling to a
>> lesser
>> degree.
>> I just got back from a week on the west coast (a near first for me)
>> and saw
>> many, many limpets.  I collected some and and still having fun
>> identifying
>> them.  I can attest to the stats discovered by our student as the
>> limpets
>> (still haven't figured out which type) I saw in one bay on rocks
>> right at
>> high tide were very highly conical, as high as a Whitecap Limpet
>> (Acmaea
>> mitra).
>> A good work on natural history of mollusks is "Living Marine
>> Molluscs", by
>> C.M. Yonge and T.E. Thompson, published in 1976 by Collins, London.
>> This book
>> has good info on limpets and may also have some more detailed
>> listings in the
>> bibliography.
>>
>> Lynn Scheu wrote:
>>
>> > I have a request for information here below. Can anyone help
>> Anthony?
>> > Please send your answers to Conch-L or to me personally at
>> > [log in to unmask]
>> >
>> > Thanks for any help,
>> >
>> > Lynn Scheu
>> > Louisville, KY
>> > [log in to unmask]
>> >
>> > > Hi there!
>> > >          I'm a third year undergraduate here in the UK, my
>> name's
>> > > Anthony Jones, i'm an environmental science student.  Recently
>> my class
>> > > took a field trip to a rockyshore habitat, there we examined the
>> shapes
>> > > of limpets within the intertidal zone, since then several
>> statistical
>> > > methods have been employed to determine if the shape of the
>> shell
>> > > varies within the intertidal zone, the results, as previously
>> thougth,
>> > > confirm that indeed they do.  Limpets being more conical at the
>> high
>> > > energy swash zone, and more flatter, with a rounder apex and the
>> sub
>> > > inter tidal zone, this was the reverse of what the students
>> expected,
>> > > our lecturer however said this was correct, he then set an
>> assignment
>> > > for us to found out why and how this change is induced, we know
>> it's
>> > > not genetic, that the change is environmentally induced, but
>> more
>> > > information is needed, i suspect it have something to do with
>> the
>> > > attachment mechanism employed by the limpet to attach itself to
>> the
>> > > substrate, but have failed to come up with any information
>> pertaining
>> > > to the explanation.  Okay any information or pointers to where
>> i'd be
>> > > able to find out about this would be much appreciated.
>> > >
>> > > Yours
>> > >
>> > > Anthony Jones
>