Sculpture is a feature of many of the shells of mollusks. It is

three-dimensional Three-dimensional space (also: 3D space, 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called ''parameters'') are required to determine the position of an element (i.e., point). This is the informal ...

ornamentation on the outer surface of the shell, as distinct from either the basic shape of the shell itself or the pattern of colouration, if any. Sculpture is a feature found in the shells of

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

s, and scaphopods. The word "sculpture" is also applied to surface features of the

aptychus An aptychus is a type of marine fossil. It is a hard anatomical structure, a sort of curved shelly plate, now understood to be part of the body of an ammonite. Paired aptychi have, on rare occasions, been found at or within the aperture of ammo ...

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

s, and to the outer surface of some

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an adje ...

opercula of marine gastropods such as some species in the family

Trochidae The Trochidae, common name top-snails or top-shells, are a family of various sized sea snails, marine gastropod molluscs in the subclass Vetigastropoda. This family is commonly known as the top-snails because in many species the shell resemb ...

. Sculpture can be

concave Concave or concavity may refer to: Science and technology * Concave lens * Concave mirror Mathematics * Concave function, the negative of a convex function * Concave polygon, a polygon which is not convex * Concave set * The concavity In ca ...

convex Convex or convexity may refer to: Science and technology * Convex lens, in optics Mathematics * Convex set, containing the whole line segment that joins points ** Convex polygon, a polygon which encloses a convex set of points ** Convex polytope ...

, incised into the surface or raised from it. Sometimes the sculpture has

microscopic The microscopic scale () is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens (optics), lens or microscope to see them clearly. In physics, the microscopic scale is sometimes regarded a ...

detailing. The term "sculpture" refers only to the

outer layer of shell, and does not include the proteinaceous periostracum, which is in some cases textured even when the underlying shell surface is smooth. In many

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

, there is no sculpture on the shell surface at all, apart from the presence of fine growth lines. The sculpture has a protective function because it increases the diameter of the shell, distributing

mechanical stress In continuum mechanics, stress is a physical quantity. It is a quantity that describes the magnitude of forces that cause deformation. Stress is defined as ''force per unit area''. When an object is pulled apart by a force it will cause elonga ...

(such as the force of a predator's jaws) across a larger surface area.

List of terms

*Axial sculpture - Sculpture running parallel to the axis of coiling, an imaginary line through the apex of a shell about which the whorls are coiled. *Bead - A small hemispherical protuberance resembling a

bead A bead is a small, decorative object that is formed in a variety of shapes and sizes of a material such as stone, bone, shell, glass, plastic, wood, or pearl and with a small hole for threading or stringing. Beads range in size from under ...

, similar to but smaller than a nodule. *Beaded - resembling rows or strings of beads. *Growth line - A fine

transverse Transverse may refer to: *Transverse engine, an engine in which the crankshaft is oriented side-to-side relative to the wheels of the vehicle *Transverse flute, a flute that is held horizontally * Transverse force (or ''Euler force''), the tangen ...

line marking the growth of the shell. *

Lira Lira is the name of several currency units. It is the current currency of Turkey and also the local name of the currencies of Lebanon and of Syria. It is also the name of several former currencies, including those of Italy, Malta and Israe ...

, lirate - ornamented with fine thread-like lines or grooves. *Longitudinal sculpture - Sculpture following the direction of the axis of the shell. *Nodule - A rounded protuberance on the shell sculpture; larger than a bead. *Nodose, Nodulose, Nodular - Bearing small rounded protuberances or tubercules. *Ornament - Can refer to surface sculpture standing out in relief on shell surface; or simply to sculpture as a whole. * Plait - Folds on the

columella Lucius Junius Moderatus Columella (; Arabic: , 4 – ) was a prominent writer on agriculture in the Roman Empire. His ' in twelve volumes has been completely preserved and forms an important source on Roman agriculture, together with the wo ...

. *Pustule - A very fine knob-like protrusion, smaller than a tubercule. *Reticulate - Sculpture consisting of a criss-crossing network of riblets, threads, or grooves. *Rib - A strong ridge on the surface of the shell. *Riblet - Smaller than a rib, but coarser than a thread. *Spiral sculpture - Sculpture following the spiral growth of the shell. *Stria (plural ''striae'') - A shallow incised groove. *Striate - Ornamented with striae. *Thread - A very fine riblet. *Transverse sculpture - Sculpture parallel to the edge of the outer lip of the

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An opt ...

. *Tubercle - Elevated knob-like projections or protrusions; larger than a pustule. *Varicose - Bearing one or more

varices A varix (pl. varices) is an abnormally dilated vessel with a tortuous course. Varices usually occur in the venous system, but may also occur in arterial or lymphatic vessels. Examples of varices include: * Varicose veins, large tortuous veins usua ...

References

{{DEFAULTSORT:Sculpture (Mollusc) Mollusc shells