Aperture : entrance or opening of the shell.
Axial : running from the apex to the base in a straight line that's not spirally.
Apex : tip of the spire in gastropods.
Beak : tip of each valve, usually pointed and near the hinge. It is the first formed part of the valve.
Body Whorl : the last and usually the largest whorl of a gastropod shell.
Callus : a thickening.
Cancellate : a criss-cross pattern of sculpture formed by radiant and concentric lines crossing each other, usually at right angles.
Cardinal teeth : hinge teeth associated with, and usually found under the beaks.
Chondrophore : are triangular shaped pit in the bivalve hinge which houses the internal ligament.
Columella : a pillar or column round with the whorls of a gastropod spiral.
Crenulate : notched, scalloped or wavy.
Ears : wing-like projections or extensions.
Escutcheon : a long, slightly sunken area in the dorsal margin posterior to the beaks. Usually set off from the rest of the shell by a difference in sculpture colour etc.
Equilateral : beaks midway between anterior and posterior ends, the anterior and posterior halves being symmetrical.
Equivalve : both valves similar in size, shape and sculpture.
Foot : a muscular organ used in locomotion and burrowing.
Gape : valves are said to gape when after closure they do not properly meet and leave a space or hole.
Growth Rings : concentric lines caused by cessation in the shell's growth at various times.
Head-foot : in Gastropods the head and foot are fused and are thus referred to as the head-foot.
Hinge : the dorsal region of the shell where the valves are joined together.
Inequilateral : beaks to one side of midline, the anterior and posterior halves thus being asymmetrical.
Inequivalve : valves are of dissimilar size, shape and sculpture.
Lateral teeth : teeth anterior or posterior to the cardinal teeth and usually some distance from the beaks. In inequilateral valves, the teeth become so distorted that it is often difficult to distinguish between laterals and cardinals.
Ligament : a band of tough elastic material uniting the two valves dorsally and maybe external, internal or both.
Lips : the aperture margins.
Linule : a slight depression in the dorsal margin in front of the beaks, it is usually heart-shaped and often set off from the rest of the shell by a difference in sculpture, color etc.
Midline : an imaginary line halfway between the anterior and posterior ends of a bivalve shell.
Nodule : a small bump.
Pallial line : the scar left by the attachment of the mantle edge to the shell.
Pallial sinus : a u-shaped notch or indentation in the pallial line caused by the attachment of siphon retractor muscles to the shell. Always opens posteriorly. Sometimes its lower margin is confluent with the pallial line.
Periostracun : a non-calcareous layer covering the outside of the shell, thin or thick but lost after death, thus usually being absent in specimens washed up on the beaches.
Radial : lines of sculpture or color starting at the beaks and radiating out to the margins.
Sculpture : ridges and grooves in the shell's surface, usually forming some sort of pattern.
Spiral : revolving, i.e., following the whorls.
Umbilicus : a small hole at the base of the columella.
Umbo : the convex part of the whorl concentrically behind the beaks.
