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The umbilicus of a shell is the axially aligned, hollow cone-shaped space within the whorls of a coiled mollusc shell. The term umbilicus is often used in descriptions of gastropod shells, i.e. it is a feature present on the ventral (or under) side of many (but not all) snail shells, including some species of sea snails, land snails, and ...
Umbilicus: in shells where the whorls move apart as they grow, on the underside of the shell there is a deep depression reaching up towards the spire; this is the umbilicus; Varix: on some mollusk shells, spaced raised and thickened vertical ribs mark the end of a period of rapid growth; these are varices
The shell is ovate and ventricose. ... The inner lip shows a callosity at the base, and partially covering the commencement of an umbilicus. [2] Distribution
In the case of shells that have an umbilicus, the columella is a hollow structure. The columella of some groups of gastropod shells can have a number of plications or folds (the columellar fold, plaits or plicae), which are usually visible when looking to the inner lip into the aperture of the shell. These folds can be wide or narrow, prominent ...
The umbilical tract is funnel-shaped, rather broad, with a central rib. The parietal wall is scarcely callous, showing the color of the base, and with a white spiral rib in the middle. [2] Normally adult and large shells are encrusted with algae. Shells washed on beaches are usually clean, exposing the underlying pearly layer below the surface.
Steromphala umbilicalis, common name the flat top shell, is a species of sea snail, a marine gastropod mollusk in the family Trochidae, the top snails. [ 1 ] Description
The shells of the species in this genus are low-spired and shaped like a button. The orbicular shell is depressed and imperforated. It is polished, porcellaneous and has a very thin pearly layer inside. The whorls are flattened above, bright, smooth or spirally grooved. The small, transverse aperture is wider than high. The thin outer lip is ...
[2] The shell is moderately elevated. The umbilicus is closed in adults, but narrowly open in juveniles. A row of foreign objects is very prominent, obscuring more than half of the dorsal surface. The base is slightly concave to almost flat, sculptured with fine, irregular, subspiral striae which run at almost right angles.