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Glossary of Terms


Although probably nowhere near comprehensive, this Glossary of Terms should help beginners and experienced shellers come to terms with some of the most-used terms in Conchology.



Acicular: needle-shaped.

Acentric: oblique, cutting growth lines at an angle.

Adductor Muscle: muscle responsible for closing the valves in bivales.

Alate: wing-like.

Anal Sulcus: notch or groove at or near posterior end of aperture.

Angulate: with an angular profile.

Annulate: with concentric rings.

Anterior: at or towards the front or head end of a shell; in gastropod shells it is the opposite end of the apex of the shell; in bivalves the anterior margin is on the opposite side of the ligament, i.e. where the foot protrudes.

Aperture: the shell opening.

Apex: posterior tip of shell.

Articulamentum: porcellaneous inner layer of chiton shell.

Articulated: (a) colour lines consisting of a series of joint-like markings; (b) valves hinged together.

Attenuate: slender tapering.

Axial: lying in-line with apex-base axis.

Axial Sculpture: shell feature or sculpture running parallel to the axis of coiling.

Axis: an imaginary line through the apex of a gastropod shell, about which the whorls are coiled.


Banding: color marking in continuous stripes.

Base: lower part, anterior side of it.

Bead: a rounded granule or tubercle.

Beak: (a) tip of the umbo in bivalves; (b) apex of a valve in chitons; (c) entire siphonal rostum in gastropods.

Bifid: divided in two by a notch or groove.

Bifurcate: forked.

Bivalve: any mollusc having two valves or shells that are hinged together, as in mussels and clams.

Body Whorl: the most recently formed whorl of a spiral shell terminating in the aperture; usually the largest whorl of a spiral shell.

Bulbous: swollen, bulb-shaped.

Byssal Notch: notch on anterior side of a bivalve through which the byssus passes.

Byssus: bunch of chitinous threads anchoring members of some bivalve groups.


Callus: a thick, usually shiny secondary deposit of calcium.

Cancellate: latticed.

Capuliform: cap-shaped, with recurved apex.

Cardinal Area: dorsal surface between hinge margin and umbo, usually bearing the external ligament.

Cardinal Tooth: a hinge-tooth situated beneath the umbo in bivalves.

Carinate: keeled.

Cephalopoda: one of the seven classes of molluscs (squids, octopus, argonauta, spirula).

Ceratus: a spur near base of outer lip.

Chambered: having divisions across the hollow of the shell, separating or dividing the shell into chambers.

Chiton: the coat-of-mail shells (Polyplacophora); they possess a shell made up of eight shell plates.

Chomata: small tubercles along edge of valves.

Cilia: microscopic filaments.

Cingulum: spiral cord, especially one bordering the suture.

Columella: central axis of a gastropod shell, lower part of inner lip.

Concentric: parallel to the line of growth.

Conchologist: one who collects and/or studies shells.

Conchology: the study of marine, fresh-water and land-shells; the arrangement and description of molluscs based upon a study of the hard parts only.

Conical: cone-shaped.

Convolute: spire completely hidden by last whorl, but not sunken to form an umbilicus.

Cordate: heart-shaped.

Cords: coarse, rounded spiral or transverse linear sculptures on the shell surface.

Corneous: horny.

Costa: a rib.

Crenate: regularly notched or scalloped.

Crenulate: with regular fine notches or folds.

Crepiduliform: slipper-shaped.

Cusp: small, often tooth-like projection.


Deltoidal: more or less triangular.

Dendritic: branched like a tree.

Dentate: toothed.

Denticle: a small tooth.

Denticulate: with small teeth.

Depressed: low in proportion to diameter.

Detritus: surface deposits, consisting largely of decaying organic matter.

Dextral: with a right-handed spiral.

Digitation: a finger-like projection.

Disjunct: successive whorls not in contact.

Distal: at the end of.

Divaricate: sculpture diverging or splitting, usually along a line.

Domed: low, broad and rather gently rounded.

Dorsal: on upper side.

Dorsal Sulcus: groove or line down centre of back in Cypraeidae.

Dorsum: back or upper side.


Edentulous/Edentulate: toothless.

Elongate: extended; considerably longer in one dimension than another.

Endemic: restricted to a certain geographical area.

Equivalve: with equal valves.

Ex Pisce: removed from the gut of a fish.


Falciform: sickle-shaped.

False Umbilicus: a shallow depression at the base of the body whorl, not penetrating into the columella.

Fasciole: band or ridge encircling the base, formed by the growth of the siphonal canal.

Fimbriated: fringed or regularly crenulated.

Fissure: slit or notch.

Flabelliform: fan-shaped.

Flame: mark that tapers to a point.

Flange: an erect, projecting flattened ridge.

Foliaceous: leaf-like.

Foramen: perforation or opening.

Fossa: deep groove.

Fossula: shallow longitudinal furrow situated towards front end of inner lip in Cypraeidae.

Fossular Ridge: ridge bordering the fossula.

Foveolated: with small pits.

Frond: leaf-like extension.

Fusiform: tapering at both ends.


Gape: space left between margins of valves when they are closed.

Gastropoda: a class of molluscs; scientific term for molluscs which have undergone torsion.

Gemmulate: with small beads.

Gibbose: very swollen, hump-backed.

Girdle: the tough mantle enclosing a chiton shell.

Globose/Globular: rounded or spherical.

Gradate: whorls rising in steps.

Granulose: with fine grain-like beads.

Growth Lines: fine axial or concentric lines indicating previous growing margin.

Guttered: with wide, shallow grooves.


Helical: spirally coiled.

Hinge Plate: platform on inner dorsal margin bearing hinge-teeth.

Holotype: the original type; the single specimen upon which a species is based.

Hyaline: semi-transparent.


Imbricate: overlapping like roof tiles.

Immersed: sunken.

Imperforate: without umbilicus.

Impressed: indented; sunken.

Incised: sculptured with one or more sharply cut grooves.

Incrustation: an irregular deposit on the shell surface.

Inductura: parietal shield.

Inflated: swolelen; stronlgy convex.

Inflexed: turned inward.

Intercostal: placed or occurring between the ribs.

Interspace: interval between ribs or ridges.

Interstices: gaps or pits between ridges or teeth.

Intervarical: between two varices.

Involute: spire completely enveloped by last whorl, leaving an apical umbilicus.

Iridescent: colours resulting from light refraction, not pigmentation.

Isodont: with a few symmetrically arranged hinge-teeth.


Jagged: with sharply uneven edge.

Junior Synonym: the later of two names.


Labial: pertaining to the inner lip.

Labium: inner lip.

Labral: pertaining to the outer lip.

Labrum: outer lip.

Lamella: a thin, flattened plate.

Lamellose: blade-like.

Lanceate: shaped like a spearhead.

Lateral: on the side.

Lectotype: a specimen subsequently selected from a series of syntypes and officially designated as such.

Lenticular: shaped like a convex-sided disc.

Ligament: horny, elastic structure joining hinges or two valves together.

Linear: long, narrow and parallel-sided.

Lira/Lirae: a ridge (ridges).

Lirate: ridged.

Lobate: with lobes.

Lunate: crescent-shaped.


Malacologist: one who studies the mollusc animal along with the shell.

Malacology: the study of molluscs (clams and snail) based on soft anatomy; the branch of zoology that deals with molluscs, the animal within the shell.

Malleate: having a hammered appearance.

Mammillate: nipple-shaped.

Mantle: fleshy fold responsible for shell growth.

Mantle Line: the line on the dorsal surface of a cowrie shell where the mantle lobes meet.

Margin: extreme edge of valve of bivalve shells; also the thickened periphery of base of some gastropods, notably cowries; sometimes used as equivalent to edge.

Median/Medial: on the mid-line.

Muricate: spiny.


Nacre: the pearly or iridescent substance which lines the interior of some molluscs shells.

Nacreous: pearly.

Naticiform: shaped like a natica.

Nebulous: cloudy.

Neotype: specimen designated as a new type when the holotype has been lost.

Node: a knob.

Nodose: knobbed.

Nodule: small knob.

Nodulose: with small knobs.

Nomenclature: a system of names.

Nuclear Whorl: whorl of the protoconch.

Nucleus: earliest part of operculum.


Obtuse: blunt.

Operculum: a horny or shelly (calcareous) plate or disc attached to the back of the foot used to close the aperture, wholly or partially, when the animal withdraws into its shell.

Ornament: surface sculpture standing out in relief on shell surface.

Ovate: oval shaped.


Palatal: pertaining to interior of outer lip.

Papilla: nipple-shaped projections.

Paratype: type-specimens, other than the holotype.

Parietal Region: part of inner lip posterior to columella.

Patelliform: limpet-shaped.

Pectinate: comb-like.

Pelagic: pertaining to or living in the open sea far from land; free-swimming or floating.

Pellucid: transparent.

Perforate: umbilicate.

Periostracum: the outer skin or horny covering on the exterior of many shells. May be thin and transparent or thick, fibrous or hairy.

Periphery: the widest part of a whorl where it bulges most.

Peristome: whole margin of aperture.

Pinnate: with side-branches.

Plait: a fold or ridge.

Plicate: ridged.

Pliculate: with fine ridges.

Posterior: the rear or tail end of an animal.

Proboscis: prolonged snout of carnivorous gastropods bearing the mouth at the tip.

Protoconch: the embryonic shell of a gastropod forming the tip of the spire.

Punctate: with punctuations.

Pupiform: barrel-shaped or swollen in the middle.

Pustulose: with pustules.

Pyriform: pear-shaped.


Radial: arranged like the spokes of a wheel.

Radula: a rasp-like organ, odontophore or lingual ribbon of armed with tooth-like processes, found in nearly all molluscs except the bivalves; this tough chitinous ribbon of teeth obtains food particles by a rasping or licking action.

Recurved: curved backwards.

Reticulate: with a network of obliquely intersecting ridges.

Rhombic: roughly diamond-shaped with rounded corners.

Rib: a ridge.

Riblet: small rib.

Rostrate: with a rostum.

Rostum: beak-like projection.

Rugose: rough or wrinkled.


Salinity: saltiness.

Scabrous: rough like a file.

Scalariform: loosely coiled, and not in contact with one another.

Scaphopoda: tusk or tooth shells; this class of molluscs possess an one-piece tapering, curved shell open at both ends and an elongated foot adapted for burrowing.

Sculpture: the decoration (in terms of ridges, ribs, striae, etc) on the surface of a shell; a pattern of raised or depressed markings on the shell's surface.

Setose: bristly.

Shell: a hard rigid, calcareous or chitinous structure encasing an animal, or covering some part of it.

Shoulder Slope: slope between shoulder and suture above.

Sinistral: having the whorls of a spiral shell turning towards the left when a shell is held with its apex pointed up and its aperture facing the viewer; this is a counter-clockwise whorl.

Sinus: notch.

Siphonal Canal or Notch: a tube-like extension or notch-like furrow in the at the anterior end of the lip in a gastropod shell.

Spatula: central area within muscle scar in limpets.

Spicule: a hard, sharp object, often needle-like.

Spiral Sculpture: a sculpture following the helical growth of a gastropod shell.

Spire: all whorls of a spiral shell exclusive of the body whorl.

Stellate: star-shaped.

Stepped: with flat shoulder so that the whorls ascend like steps.

Striae: fine lines, threads or grooves.

Striate: with striae.

Stromboid Notch: with a shallow notch near base of outer lip in Strombidae.

Subulate: tapering very gradually to a sharp point.

Sulcate: grooved.

Sulcus: a groove.

Suture: the spiral groove where two adjacent whorls are joined.

Syntype: any specimen from a type-series for which no holotype was designated.


Tabulate: flat-topped.

Taxon/Taxa: group of organisms with own scientific name.

Teleoconch: all the whorls of a gastropod shell after the protoconch.

Thread: fine ridge.

Transverse: at right angles to main axis.

Trema: a hole in the shell for the exhalent current in haliotis shells.

Trochiform: top-shaped with flat sides.

Truncate: ending abruptly.

Tubercle: elevated knob.

Tuberculate: knobbed.

Turbiniform: top-shaped with convex sides.

Turriculate: sharply conical with numerous, rather flattened whorls.


Umbilicate: navel-like; with depressed cavity.

Umbilicus: a perforation, usually in the base of the central axis.

Umbo: the curved dorsal peak of a valve.

Undulate: having a wavy surface.

Univalve: a mollusc consisting of a single spirally coiled shell.


Valve: one of the separate portions of a shell of a mollusc.  In bivalves, one of the two portions into which the shell is divided, the two valves usually joined by a hinge. In chitons, one of the eight plates comprising the shell.

Varical: pertaining to a varix.

Varix: a rib-like thickening of the outer lip due to periodic arrested growth of the shell.

Ventral: on the underside.

Ventricose: strongly swollen.

Verrucose: with wart-like tubercules.

Vesicle: a bubble-like sac or hollow chamber.

Vitreous: glassy.

Volution: a whorl.


Whorl: a single, complete turn of 360° in the spiral growth of a gastropod shell.

Wing: prominent angular extension of the dorsal margin in a bivalve.


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