| Term | Definition |
| INVOLUTE | Having the last whorl enveloping earlier ones, so that the height of the APERTURE is generally the height of the shell, as in the Bullidae; see also: CONVOLUTE. See other gastropod shapes. | |
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| SPIRE, INVOLUTE | The condition of having the POSTNUCLEAR WHORLS higher than, and enveloped by the NUCLEAR WHORLS; see also: SPIRE, SUNKEN. | |