The top of the shell; first formed part of gastropod shell, typically bearing the protoconch.


Thickened shelly layer typically covering part of the columella and/or umbilicus.


A central pillar or column that extends from the apex to the bottom of the shell. The shell twists around this pillar.

Collumellar lip

Inner part of the shell aperture overlaying columella.


Presence of small denticles along the edge of the teeth of the radula; can give the impression of a serrated edge.

Gizzard (gizzard plates)

A modified region of the digestive tract used for gridding food. It may bear three or four calcified or chitinous plates.

Involute apex (involute spire)

When the apex is sunken and surrounded by the whorls of the shell.


A nipple-like extension of the spire; term often used when the protoconch protrudes over a flat spire.


The tissue that surrounds the visceral mass of molluscs; secretes the shell.

Pallial lobe

An extension of the mantel under the gastropod; can function as an accessory foot.

Parapodial lobe

Side extensions of the foot, which fold over the sides of the body of the animal or shell. Used to protect the shell or swim.


A chitinous-like outer layer on the surface of the shell. Often thin; may be coloured.


Larval shell; the oldest part of the shell. Often situated in the apex or absorbed into the shell during formation of shell whorls.


A ribbon of chitin bearing teeth in regular longitudinal and transverse rows. Located in the buccal cavity.


Surface structure and ornamentation of shell.

Spiral lines or groves

Possible elements of the sculpture of the shell; spiral impressions or grooves in the shell in the form of dots, chain-like lines, or simply depressions.


Shell whorls that are raised in a spiral shape. Does not include the last whorl containing the aperture.

Umbilicus (umbilical canal, umbilicate)

A cavity or depression of varying depth at the base of the shell.