Editing Gastropoda (section)

=== Shell ===
[[File:Zonitoides nitidus shell (cropped).jpg|thumb|The shell of ''[[Zonitoides nitidus]]'', a small land snail, has [[Gastropod shell#Chirality|dextral coiling]], which is typical (but not universal) of [[gastropod shell]]s.]]
[[File:Physella_acuta_01.JPG|thumb|The shell of ''[[Physella acuta]]'', a freshwater snail, which is left-coiling ([[Gastropod shell#Chirality|sinistral]]).]]
{{main|Gastropod shell}}

Most shelled gastropods have a one piece [[Gastropod shell|shell]] (with exceptional [[Juliidae|bivalved gastropods]]), typically coiled or spiraled, at least in the larval stage. This coiled shell usually opens on the right-hand side (as viewed with the shell [[apex (mollusc)|apex]] pointing upward). Numerous species have an [[operculum (gastropod)|operculum]], which in many species acts as a trapdoor to close the shell. This is usually made of a horn-like material, but in some molluscs it is calcareous. In the land slugs, the shell is reduced or absent, and the body is streamlined.

Some gastropods have adult shells which are bottom heavy due to the presence of a thick, often broad, convex ventral callus deposit on the inner lip and adapical to the aperture which may be important for gravitational stability.<ref>{{cite journal|author1=Geerat J. Vermeij|title=The balanced life: evolution of ventral shell weighting in gastropods|journal=Zoological Journal of the Linnean Society|volume=194|issue=1|year=2022|pages=256–275|url=https://doi.org/10.1093/zoolinnean/zlab019|doi=10.1093/zoolinnean/zlab019|access-date=2022-01-04|archive-date=2023-08-23|archive-url=https://web.archive.org/web/20230823114009/https://academic.oup.com/zoolinnean/article/194/1/256/6261015|url-status=live}}</ref>