evoluta

Evoluta is a term encountered in Portuguese-language malacology and conchology that describes a shell morphology in which the whorls of a gastropod shell are exposed and visible, rather than tightly concealed by subsequent whorls. In practice, evolute shells show clearly the progression of coils from the apex to the aperture, with the outer whorls not fully enveloping the earlier coils.

In evolute shells, the sutures are typically well defined and visible, and the overall spiral may appear more open or spread out compared with shells whose whorls overlap extensively. This contrasts with involute shells, where newer whorls envelop the older ones and much of the interior coils becomes hidden from view. The term is used in descriptive work on both fossil and living gastropods, across various families.

Etymology and usage: Evoluta derives from Latin evolutus, meaning unfolded or unrolled. In English-language malacology, the corresponding adjective is evolute, and the noun phrase “evolute shell” is used to describe this coil pattern. In Portuguese-language scientific writing, evoluta can function as the descriptive form and may appear as part of species descriptions or as a common-name reference for certain shell forms.

See also: conchology, gastropod, gastropod shell morphology, involute shell.