Diagram of Gastropod Shell and Glossary of Terms

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Glossary

ABAPICAL. Away from the shell apex toward the base, along the axis or slightly oblique to it.
ABAXIAL. Outward, away from the shell axis.
ACICULATE. Needle shaped.
ACULIATE. Very sharply pointed; prickly.
ADAPICAL. Toward the shell apex along the axis or slightly oblique to it.
ADAXIAL. Inward toward the shell axis.
ADNATE. Growing together, connected.
ANNULAR. Made up of rings.
APERTURE (or MOUTH). The opening of the shell of a gastropod, providing the outlet for the soft parts of the animal.
APEX. First-formed end of a gastropod shell, usually the extreme point of the shell.
APICAL ANGLE. In the plane through the axis, the angle subtended between two straight lines that touch adjacent whorls on opposite sides near the apex; identical with the spire angle if the whorls increase at a regular rate.
AXIAL. Parallel with the shell axis.
AXIS. Imaginary line vertically through the apex, around which the whorls are coiled.
    
BASAL CREST. External angulation at base of body whorl in the shell of some gastropods.
BODY WHORL. Last-formed, complete coil of shell of gastropods.
    
CALLUS. Smooth interior lining of pale shelly material, frequently obvious within the mouth of a gastropod, e.g., as a coating on the parietal area.
CANAL. Narrow, subtubular extension of the aperture cf. 'SIPHONAL CANAL'.
CANCELLATE. Having an ornament of intersecting spiral and transverse threads or cords.
CARINA. Prominent spiral ridge or keel.
CARINATE. Bearing a keel (carina).
CHANNELLED. Sharply sunken below the general surface (e.g., a channelled suture)
CLAUSILIUM. Spoon-shaped flexible plate which functions as an operculum in the family Clausiliidae.
COELOCONOID. Approaching conical, but with concave sides.
COLUMELLA. Solid or hollow pillar surrounding the axis in coiled gastropod shells, formed by the inner walls of the whorls.
COLUMELLAR. Referring to that part of the interior surface of the shell, comprising the columella.
COLUMELLAR FOLD. Spirally wound ridge on the columella that projects into the shell interior.
COLUMELLAR LIP. Adaxial part of the inner lip comprising the visible terminal part of the columella.
CONCENTRIC. With direction coinciding with that of the growth lines.
CONCHIOLIN. Protein of which the periostacum and organic matrix of the calcareous parts of the shell are composed.
CONISPIRAL. With spire projecting as a cone or conoid.
CONVOLUTE. With the last whorl completely embracing and concealing the earlier ones.
CORD. Round topped, moderately coarse spiral or transverse linear elevation on the shell surface.
CORONATE. Bearing tubercles or nodes at the shoulder of the whorls.
COSTA (Plural: COSTAE) Round topped elevation of moderate width and prominence (greater than a cord) on the shell surface, parallel to the outer lip.
COSTATE. Having costae.
CRENATE. With notches along an edge, rib or the lip.
CRISPATE. With a crinkled edge or margin.
CUNIFORM. Wedge shaped.
CYRTOCONOID. Approaching a cone in shape, but with convex sides.

DECOLLATE. Apical whorls missing, eroded or discarded.
DENTICLE. Small round or oval "tooth" on the interior surface of some gastropod shells, often on or just within the mouth edge.
DEXTRAL. The right-handed coiling of some gastropods; when the mouth is on the observer's right and the apex is directed upwards, and with the mouth facing the observer. (cf. SINISTRAL)
DIAMETER. The distance between two planes parallel with each other and with the shell axis, which touch opposite sides of the shell.
DIGITATION. Fingerlike outward projection from the outer lip.
DISCOIDAL. Approaching a disc in form; axially compressed.
DISTAL. Away from the central axis or from the apex.
        
EDENTULOUS. Lacking teeth.
ELEVATED. High in proportion to the diameter.
EPIPHRAGM. Dry mucus sheet, temporarily used to close the mouth of some gastropods. In some large snails it may be thickened with lime and consequently opaque.
    
FIMBRIATE. Puckered.
FOLD. Spiral ridge on interior of shell wall.
FORAMEN. An opening or hole.
FULVOUS. Orange in colour.
FUSIFORM. Slender, spindle-shaped, tapering almost equally towards both ends from a maximum diameter (e.g. the shell shape of Clausiliidae).
    
GIBBOUS. Very convex or tumid. (Also GIBBUS)
GRANULATED. Covered with small grains or tubercles.
GROWTH-LINES. In gastropods, surface markings left in the former positions of the mouth-edge.
    
HELICONE. Coiled tube that forms most gastropod shells, which expands as it grows.
HETEROSTROPHIC. Condition of the protoconch when the whorls appear to be coiled in the opposite direction to those of the teleconch.
HIRSUTE. Hairy.
HOLOTYPE. The single specimen on which the description of the species is based.
HYALINE. Glossy, transparent, vitreous.

IMBRICATE. Overlapping like tiles or shingles on a roof.
IMMERSED. Condition of initial whorls when sunk within the later ones and concealed by them.
IMPRESSED. Condition of suture having both ajoined whorl surfaces turned inward adaxially.
INCREMENTAL ANGLE. In the plane through the entire axis, the angle between two straight lines that touch contiguous whorls on opposite sides at the part of the shell in question.
INDUCTURA. Smooth shelly layer secreted by the general surface of the mantle, commonly extending from the inner side of the aperture over the parietal region, columellar lip and part or all of the shell exterior (e.g. Cypraea).
INNER LIP. Referring to the inner part of the mouth-edge from the base of  the columella to the suture.
INVOLUTE. The last whorl enveloping earlier ones so that the height of the aperture corresponds to that of the shell.
    
KEEL. In connection with shells of snails, the periphery of a whorl extended to form a more or less flattened plate; a prominent spiral ridge (cf. CARINA). In connection with slugs, it is a raised ridge in the midline of the body ending at the tail, where it is most prominent.
    
LABIAL AREA. Flattened or callus coated surface extending from the inner lip.
LABIUM. See INNER LIP.
LABRUM. See OUTER LIP.
LAMELLA (Plural LAMELLAE). Thin plate; generally applied to spiral structures on the interior of the shell wall, especially in the Clausiliidae.
LANCEOLATE. Shaped like a lance head, i.e. sharply pointed at one end, broader at the other.
LAST WHORL. Last formed complete volution of the helicone.
LEFT. Side of the shell on the left when the shell is orientated with the aperture facing the observer and the apex upward.
LIP. Thickened or reflected mouth edge, present only in adult  shells of some species.
LIRA. Fine linear elevation on shell surface or within outer lip.
    
MACULATE. Splashed, spotted or blotched.
MAMMILATE. Dome shaped protuberance as a shell ornament or protoconch shape.
MANTLE.In snails, the fleshy or membranous outgrowth of the body wall which secretes the shell. In terrestrial slugs, the flap of skin and tissue covering part of the body like a "saddle" and enclosing the lung.
MARGINATE. Outer lip with a strengthening rib.
MONILIFORM. Shaped like a row of beads like a necklace.
MOUTH. Opening of the shell, providing the outlet for the soft parts.
MOUTH-EDGE (or PERISTOME). Shell edge around the mouth.
MURICATE. With sharp, elevated points.

NACREOUS. Type of shell structure consisting of thin leaves of aragonite parallel to the inner surface of the shell and exhibiting its characteristic lustre; pearly.
NODOSE. With small, knoblike protuberences.
NUCLEUS. Earliest formed part of shell or operculum.
  
OPERCULUM. Horny or calcareous plate carried by the foot and serving to close the mouth when the animal is withdrawn into the shell.
OPISTHOCLINE. Shell growth lines sinuous.
ORNAMENT. Relief pattern on the surface of many shells.
ORTHOCLINE. Shell growth lines nearly vertical.
ORTHOSTROPHIC. Condition of the protoconch which is coiled in the normal manner, not heterostrophic.
OSTRACUM. The calcareous part of the shell beneath the periostracum.
OUTER LIP. Abaxial margin of the aperture, extending from the suture to the base of the columella.
OVATE. Egg shaped.
    
PALATAL. Referring to that part of the interior surface of the shell within the outer mouth-edge from the suture to the base of the columella.
PARATYPE. A specimen, other than the holotype, upon which the description of the species was based.
PARIETAL. Referring to that part of the interior surface of the gastropod shell between the columella and the suture – in effect, formerly the external surface of the earlier-formed whorls.
PARIETAL CALLUS. Callus on the inner parietal region which may extend on to the previous whorl.
PARIETAL FOLD (LIRA, PLICA) Spirally wound ridge on the parietal region that projects into the shell interior.
PATELLIFORM. Limpet shaped.
PAUCISPIRAL. With relatively few whorls.
PERFORATE. With umbilicus. (Inappropriate usage in the literature because the umbilicus is not a perforation.)
PERIPHERY. Part of any particular whorl furthest from the axis.
PERIOSTRACUM. Horny organic coat covering the calcareous part of the shell or ostracum.
PERIPHERY. Part of whorl furthest from the axis.
PERISTOME. Shell edge around the mouth.
PLICA. Fold or costa involving the entire thickness of the wall of the shell.
PORCELLANEOUS. With a tranparent pocellain-like appearance.
PNEUMOSTOME. The external opening of the lung in terrestrial slugs, on the right side of the mantle.
PROSOCLINE. Shell growth lines at an angle, so that the adapical end lies further forward (i.e. nearer the base of the shell spiral) than the abapical end.
PROTOCONCH. Apical whorls of the shell, especially where clearly demarcated from later ones; in land molluscs, that part of the shell formed within the egg.
PROXIMAL. Towards the centre of the shell.
PUNCTATE. With pinprick-like depressions.
PUPAEFORM. Elongate oval.
PYRIFORM. Pear shaped.
    
REFLECTED. Turned outwards at the margin – referring to the mouth-edge.
RETICULATE. Forming a network of obliquely intersecting sculptural elements.
RIB. Projecting ridge on shell, usually transverse (on external surface unless otherwise indicated).
RIDGE. Extended, somewhat angular linear elevation on the shell surface.
RIMATE. Consisting of a very narrow cavity, referring commonly to the umbilicus.
ROSTRUM. Attenuated extremity.
    
SCALARIFORM. Whorls disjoined or tending to become so.
SCULPTURE. Relief pattern on shell surface. The same as ornament.
SELENIZONE. Spiral band of concentric growth lines or threads generated by a narrow notch or slit near the top of the outer lip.
SHOULDER. Angulation near upper margin of whorl.
SINISTRAL. Left-handed coil; mouth on observer's left when apex is directed upwards, and with mouth facing the observer. (cf. DEXTRAL)
SINUS. Indentation at the margin of the mouth.
SIPHON. Tubelike extension of the mantle for the passage of inhalent or exhalent current.
SIPHONAL CANAL. Tubular or troughlike extension of the anterior (abaxial) part of the apertural margin for inclusion of the inhalent siphon.
SIPHONAL FASCIOLE. Distinctive band of abruptly curved growth lines near the foot of the columella marking the successive positions of the siphonal notch.
SIPHONAL FOLD. Ridge corresponding to the siphonal notch wound spirally around the columella.
SIPHONAL NOTCH. Narrow sinus of the apertural margin near the foot of the columella serving for the protusion of the inhalent siphon.
SPIRAL. Passing continuously around whorls, parallel to the suture. (cf. TRANSVERSE).
SPIRE. In gastropods, the visible part of all the whorls except  the body whorl.
SPIRE ANGLE. In a plane through the entire shell axis, angle between the two straight lines which touch all whorls on opposite sides; such lines can only be drawn if the rate of increase is constant.
SQUAMOSE. With scales.
STRIA (Plural STRIAE). Fine incised groove on shell surface.
STYLIFORM. Parallel sided except at sharp pointed apex.
SUBMERGED. Initial whorls sunk in later ones. Same as IMMERSED.
SUBULATE. Slender and tapering to a point, sides convex; awl shaped.
SULCUS. Radial depression of surface of the shell.
SUTURAL SLOPE. Angle between suture and plane perpendicular to the axis.
SUTURE. Continuous spiral line on shell surface where the whorls join.
    
TELEOCONCH. Entire shell, exclusive of the protoconch.
TOOTH. General term for shelly prominence on interior surface of shell of a gastropod. (See DENTICLE, FOLD , LAMELLA).
TRANSVERSE. Crossing the direction of shell growth, usually parallel with growth-lines (cf. SPIRAL)
TREMA (Plural: TREMATA). Orifice in outer wall of some shells for excretory function, occurs singly or in a series.
TRUNCATE. With curvature of outline interrupted by a straight cut.
TUBERCLE. Moderately prominent smal rounded elevation on a shell surface.
TUMID. Swollen or inflated in shape.
TURRETED. With a stepped profile.
TYPE. Any specimen(s) upon which the description of a species is based.          

UMBILICATE. With an umbilicus.
UMBILICUS. Cavity surrounding the axis, opening at the base of the shell.

VARICOSE. Bearing a varix or varices.
VARIX (Plural: VARICES). Transverse elevation more prominent than costa and generally spaced more widely; it is evidence of a growth halt during which a thickened outer lip developed.
VENTRICOSE. Strongly inflated.
VOLUTION. Any complete coil of the helicone.
    
WALL. Any part of the framework of the shell.
WHORL. Any complete coil of the gastropod shell. How to count whorls

SOURCES OF TEXT:
Moore, R.C. (ed.), 1960. Treatise on Invertebrate Palaentology. Part I, part 1. Lawrence, Kansas, Kansas University Press and Geological Society of America. pp. 126-135.
Moore, R.C. (ed.), 1960. Treatise on Invertebrate Palaentology. Part N, part 1. Lawrence, Kansas, Kansas University Press and Geological Society of America. pp. 102-109.
Pain, T. (?1960). A short glossary of molluscan terms. London, Conchological Society of Great Britain and Ireland. Papers for Students, no. 4.