page_title: Gastropod shell
section_title: Shape of the shell
hierarchical_section_title: Gastropod shell / Shape of the shell
caption_attribution_description: English: Schematic representation/drawing of the apical, apertural and basal view of the shell (probably Trochulus sp.) shows of the 14 measurements. Dotted lines represent orientation axes. N complete whorls P partail whorls NTW computed as the number of complete whorls plus the partial whorl (in degrees; divided by 360) APX the width of the apex SP1 the width of the first whorl SP2 the width of the second whorl SP3 the width of the third whorl DWL the diameter of the spire without the last whorl HSP the height of the spire HFW the height of the first whorl DPR the diameter of the peristome HPR the height of the peristome DSP the diameter of the spire AES the shape, measured as the angle formed by the apex and the most external sutures DOM the diameter of the umbilicus WWO the width of the shell without the opening
context_page_description: The gastropod shell is part of the body of a gastropod or snail, a kind of mollusc. The shell is an exoskeleton, which protects from predators, mechanical damage, and dehydration, but also serves for muscle attachment and calcium storage. Some gastropods appear shell-less but may have a remnant within the mantle, or the shell is reduced such that the body cannot be retracted within. Some snails also possess an operculum that seals the opening of the shell, known as the aperture, which provides further protection. The study of mollusc shells is known as conchology. The biological study of gastropods, and other molluscs in general, is malacology. Shell morphology terms vary by species group. An excellent source for terminology of the gastropod shell is "How to Know the Eastern Land Snails" by John B. Burch now freely available at the Hathi Trust Digital Library.
context_section_description: The overall shape of the shell varies. For example, three groups can be distinguished based on the height – width ratio:
  oblong – the height is much bigger than the width
  globose or conical shell – the height and the width of the shell are approximately the same
  depressed – the width is much bigger than the height
  The following are the principal modifications of form in the gastropod shell.
  Regularly spiral:
  Bulloid: bubble-shaped Bulla
  Coeloconoid a slightly concave conical shell in which the incremental angle increases steadily during growth (see: Calliostoma)
  Cone-shaped, obconic. Conus 
  Contabulate, short, with shouldered whorls
  Convolute: aperture as long as the shell, nearly or quite concealing the spire. Cypraea
  Cylindrical, pupiform. Lioplax, Pupa
  Cyrtoconoid: approaching a conical shape but with convex sides (see: Gibbula)
  Depressed, lenticular. Ethalia carneolata
  Discoidal. Elachorbis
  Ear-shaped. Haliotis
  Elongated, subulate, elevated. Terebra
  Few-whorled. Helix pomatia.
  Fusiform, spindle-shaped. Fusinus
  Gibbous. Whorls swelled beyond the normal contour of increase (usually on the aperture side ). Streptaxis.
  Globular. Natica
  Many-whorled. Millerelix peregrina.
  Short, bucciniform. Buccinum
  Trochiform, pyramidal, conical with a flat base. Trochus
  Turbinated: conical, with rounded base. Turbo
  Turreted, turriculate, babylonic; an elongated shell with the whorls angulated or shouldered on their upper part. Turritella
  Scalariform, whorls not impinging. Epitonium scalare
  Irregularly spiral, evolute. Siliquaria,  Vermetus
  Tubular.
  Shield-shaped. Umbraculum
  Boat-shaped, slipper-shaped. Crepidula
  Conical or limpet-shaped. Patella
  Biconic: shaped like two conical shapes that are touching their bases, and tapering at both ends: Fasciolaria tulipa
  Pear-shaped: a combination of two shapes: ovate-conic and conic. Ficus
  Detailed distinction of the shape can be:
caption: Schematic representation of the apical, apertural and basal view of a shell, showing 14 different commonly used measurements. Dotted lines represent the orientation axes (except of lower image).
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