Limpet

Limpet (Patella), a genus of Gasteropod Molluscs, in the Zygobranch section. The animals are most familiar objects between tide-marks on rocky coasts, are covered by a conical shell, with the apex directed slightly forward, and remain firmly fixed when the tide is out, adhering by the large oval or circular 'foot,' which acts like a vacuum-sucker on the rock. How firmly they adhere, unless taken by surprise, every wanderer on the shore has tested, yet the 'oyster-catcher' (Hæmatopus) manages with adroitness to detach them. They move slowly about under water, browsing on crusty seaweeds with the help of a peculiarly long 'radula' or rasping ribbon, which in the common limpet (P. vulgaris) is much longer than the body, and bears 160 rows of teeth, 12 in each row, 1920 in all. It is noteworthy that the limpets show a certain local memory, for they return after a short journey to their old resting-places, which, after prolonged usage, may be marked by distinct depressions, especially if the rock be calcareous. The gills form a circle of leaflets between the foot and the edge of the mantle; the internal structure is complex after the fashion of gastropods; the sexes are distinct, and breed in spring. Limpets are occasionally used for food, but oftener for bait. 'A species found on the western coast of South America has a shell a foot wide, which is often used as a basin.' There are numerous species of Patella, and many allied genera, though it is not yet demonstrated that all the forms usually associated with Patella deserve the place which their shells and raspers suggest. The key-hole limpets (Fissurellidæ) form an adjacent family, marked externally by a hole at or near the apex of the shell, or by a notch on the anterior margin. Another externally similar but more remote set of 'limpets' are united in the family Acmaidæ, of which Acma testudinalis is very common on the northern coasts of North America. They are often called 'slipper-limpets,' from the presence of an internal flange on the incipiently spiral shell, and are generally attached, sometimes as commensals, to other molluscs. The genera Calyptrea and Crucibulum, nearly related to the above, are known as 'cup-and-saucer-limpets.' For anatomy, see R. J. Harvey Gibson, Transactions Royal Society, Edin., 1884-85.