Wooster’s Fossil of the Week: an Italian keyhole limpet (Pliocene of Cyprus)

This week’s fossil is a beautiful little gastropod (snail) scientifically known as Diodora italica (Defrance, 1820), and commonly as the Italian Keyhole Limpet. I collected it with Steve Dornbos (’97) during the 1996 Keck Geology Expedition to Cyprus, where it was part of Steve’s Independent Study project describing a Pliocene reef.
Diodora italica belongs to the Family Fissurellidae and is not a “true limpet”. The hole at the top gives it away as something different than the usual simple cap-like limpet shell. Several gastropod groups have evolutionarily converged on the flat shell because it is efficient at withstanding the stresses of strong waves and, curiously, the high pressures in the deep sea. Diodora is still alive, as you can see in this nice (and copyrighted) image.

The hole at the top of the shell, the “keyhole”, is part of the respiration system of these snails. They take in water under the edge of the shell, pass it over a pair of gills, and then send the used water out the “chimney” of the keyhole.

Keyhole limpets scrape algae and bacteria from rock surfaces, using the strong foot to adhere to the substrate

Diodora italica was described by the oh-so-French naturalist and collector Jacques Louis Marin Defrance (1758-1850). I can’t find much about him, but there is a nice portrait!


McLean, J.H. 1984. Shell reduction and loss in fissurellids: a review of genera and species in the Fissurellidae group. American Malacological Bulletin 2: 21–34.

Murdock, G.R. and Vogel, S. 1978. Hydrodynamic induction of water flow through a keyhole limpet (Gastropoda, Fissurellidae). Comparative Biochemistry and Physiology Part A: Physiology 61(2): 227–231.

About Mark Wilson

Mark Wilson is a Professor of Geology at The College of Wooster. He specializes in invertebrate paleontology, carbonate sedimentology, and stratigraphy. He also is an expert on pseudoscience, especially creationism.
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