parietal callus

{{short description|Shell anatomy of some groups of snails}}

Image:Semicassis pyrum (base).JPG has a large parietal callus, at the top in this image]]

Image:Cymatium pileare.jpg has a narrow parietal callus around the surface of the aperture nearest the columella, on the left of the shell opening as it is shown here]]

A parietal callus is a feature of the shell anatomy of some groups of snails, i.e. gastropods. It is a thickened calcareous deposit which may be present on the parietal wall of the aperture of the adult shell. The parietal wall is the margin of the aperture and part of the wall of the body whorl that is closest to the columella. The callus is often smooth and glossy, but can also be decorated with raised ribs or wrinkles.{{Citation needed|date=March 2025}}

This feature is found in such marine families as Ranellidae (pictured), Cassidae, Nassariidae, Ringiculidae and others. It is also found in some families of land snails, terrestrial pulmonates.{{Citation needed|date=March 2025}}

The callus is often "glazed", to help the animal slide in and out of the shell more easily.{{Cite web |last=Leal |first=José H. |date=2024-03-01 |title=The Fossil Conch and its Barnacles |url=https://www.shellmuseum.org/post/the-fossil-conch-and-its-barnacles |access-date=2025-03-11 |website=Baily Matthews National Shell Museum & Aquariu |language=en}}

When the callus covers of 50% of the surface area of the ventral part of the shell, it is called an "extreme parietal callus".{{Cite journal |last=San Jose State University |last2=Pietsch |first2=Carlie |last3=Anderson |first3=Brendan M. |last4=Maistros |first4=Lauren M. |last5=Agelvis |first5=Mariana |last6=Allmon |first6=Warren D. |date=2017 |title=EVALUATING ECOLOGICAL FUNCTION AND CONVERGENT EVOLUTION OF EXTREME PARIETAL CALLUS IN MARINE GASTROPODS |url=https://gsa.confex.com/gsa/2017AM/webprogram/Paper307057.html |journal=Conference: Geological Society of America Annual Meeting |doi=10.1130/abs/2017AM-307057|url-access=subscription }}