Tall shell from dry, un-shaded rock on the upper shore. Low shells from damp situation under the shade of a bridge, and near low water mark so out of water for a short time each day. As none of the shells experienced exposure to wave action, their different profiles are not a response to differences in wave impact. Aerial view of site at www.google.co.uk/maps/@53.2220482,-4.1715085,2163m/data=!…

Fretter & Graham (1962) wrote,
“The shells of limpets that live at a high level on the shore are, at an adult stage, taller than those — near low water level or in rock pools. — Orton (1929 & 1932) correlated these differences with differences in the degree of exposure to desiccation. —Orton suggested that the tall spire with relatively narrow base is produced by the limpet which holds close to the rock to prevent desiccation. —downpull of the muscles during –exposure pulls in the mantle skirt which is responsible for new growth at the margin of the shell. — a smaller peripheral increment will be made — than by others living lower on the shore [moister and exposed for shorter period] or in rock pools in which the shell muscles are relaxed. Very occasionally, a shell is encircled by a ledge — which is due to an abrupt change in the angle of growth and indicates a sudden change from a dry to a damp habitat” [See Patella vulgata; shell from a rocky islet in North Wales. ]

For low and tall profile shells on a shore exposed to strong wave action see Patella vulgata; tall and low profile shells from the north tip of the Great Orme, Wales, which is exposed to strong wave action.

References

Fish, J. D. & Fish, S. 1989. A student’s guide to the seashore. London, Unwin Hyman. p. 196.

Fretter, V. and Graham, A. 1962. British prosobranch molluscs: their functional anatomy and ecology. Ray Society, London. pp. 501-502.

Orton, J. H. 1929. Observations on Patella vulgata Part III. Habitat and habits. J. mar. biol. Ass. UK. 16: 277-288..

Orton, J. H. 1932. Studies on the relation between organisms and environment. Proc. Lpool. biol. Soc., 46: 1-16 .

Yonge, C. M. 1947, revised 1966. The sea shore. London, New Naturalist, Collins. pp. 115-120.