Glossary

The projecting part of a bivalve shell that is equivalent to the first formed part of the shell (the terms beak and umbo are more or less interchangeable).

Benthos:

The community on the floor of a lake, river or stream (or on the ocean floor).

Biconcave:

Concave above and below.

Bifid:

A structure divided into two projections.

Bifurcate:

Branching into two projections.

Billabong:

A cut-off lake formed by a meandering river (also called oxbow lakes).

Bilobed:

With two lobes.

Biramous:

Divided into two branches.

Bivalve:

A shell composed of two valves - also refers to members of the class Bivalvia.

Bivalvia:

Class of molluscs characterised by having two articulated valves.

Brackish:

Water with a salinity in between fresh water and seawater.

Branchial:

Relating to the gills.

Branchial siphon:

The inhalant (ventral) siphon of a bivalve.

Brood chamber:

An chamber within the animal or part of the shell in which eggs are brooded.

Bursa copulatrix:

A sperm sac in which sperm is deposited - usually directly by the copulating partner. See also spermathecal gland.

Bursal duct:

The duct of the bursa copulatrix.

Byssal:

See byssus.

Byssus:

One or more attachment threads produced by the byssal gland in the foot of many autobranch bivalves

Caecum:

Pouch-like projection from a chamber, such as the stomach.

Calcareous:

Primarily consisting of the mineral calcium carbonate (CaCO₃).

Callus:

Part (such as of the shell) that has thickened and/or hardened.

Canaliculated:

Forming a channel.

Capsule gland:

A gland associated with the oviduct.

Cardinal tooth:

Short teeth that radiate from the umbo of a bivalve - part of a heterodont hinge.

Carina:

A prominent spiral ridge.

Carinate:

With one or more carinae.

Central tooth:

The middle tooth of each row of teeth of the radula. Sometimes called the rhacidian tooth.

Cephalic:

Pertaining to the head.

Chevron:

An inverted V-shape.

Chitin:

A polymer similar in structure to glucose. Combined with protein it forms the exoskeleton in many invertebrates.

Chondrophore:

A spoon-shaped structure on a bivalve hinge that contains the internal ligament.

Cilia:

Thin processes that extend from epithelial cells - usually motile but some are stationary.

Ciliary feeding:

Feeding where food is captured on the gills using the cilia on the gill filaments – often called filter feeding or suspension feeding.

Ciliate:

Bearing cilia, or a type of protozoan.

Ciliated:

With cilia.

Class:

A rank within the hierarchy of taxonomic classification. It is the main category between phylum and order.

Classification:

A process of establishing, defining and ranking taxa within hierarchical series of groups.

Clonal:

Embryos or adults that share an identical common ancestry (i.e., not produced by sexual reproduction).

Collabral:

Growth lines that conform to the shape of the outer lip of a gastropod aperture or the edge of a bivalve shell.

Columella:

The central column of a gastropod shell, visible in an intact shell as part of the inner apertural lip.

Columellar:

Relating to the columella of a gastropod.

Commensal:

A commensal relationship is where one species lives symbiotically with another species where one obtains benefits (e.g., shelter, food) and does not harm or benefit the other.

Concentric:

Lines with a common centre.

Conic:

Of conical shape.

Conical:

In the shape of a cone.

Connective tissue:

Tissue that connects, binds or supports organs and other tissues (usually rather amorphous).

Conspecific:

Of the same species.

Convolute:

Twisted or coiled.

Copulatory organ:

A section or part of the body used to facilitate internal fertilisation by transferring sperm.

Costae:

Distinct but fine ribbing.

Cryptic:

Hidden or camouflaged.

Crystalline style:

A hyaline rod of mucoprotein found in the style sac of some gastropods and many bivalves.

Ctenidial filaments:

The filaments that make up the ctenidium.

Ctenidium:

The original molluscan gill (secondary gills are also found in molluscs) which is comprised of filaments. It is paired in bivalves and in its primitive state in gastropods, although all freshwater gastropods have a single ctenidium or none.

Decollate:

Condition where the top part of the gastropod spire is missing.

Demibranch:

Half of a bivalve ctenidial filament - these are typically W- shaped and divided into a V-shaped inner and outer demibranch.

Denticle:

A small projection.

Denticulate:

Toothed, or with short ridges.

Depressed:

Somewhat flattened.

Detritus:

Particulate organic material.

Dextral:

Coiled to the right (cf. sinistral).

Diaphragm:

A partition.

Diatom:

A single-celled ‘alga’ with a silicate cell wall – an important component of plankton. They belong to the class Bacillariophyceae in the phylum Ochrophyta.

Diaulic:

With two ducts.

Dimorphism:

Two forms (usally based on size) of the same species. Mostly related to sex (sexual dimorphism) but can be used for other morphotypes such as colour or shape. Compare with polymorphism.

Dimyarian:

With two adductor muscles (in bivalves).

Dioecious:

Having separate sexes (male and female).

Direct development:

When an embryo develops through to hatching as a juvenile without going through a free-living larval stage.

Disjunct:

Not joining or meeting. Often applied to distributions.

Distal:

Away from the middle of the body or point of attachment.

Diverticulate:

With a diverticulum.

Diverticulum:

Blind process or pocket.

Dorsal:

The surface of an animal furthest away from the ground or other support, in other words upper surface.

Dorso-lateral:

On the upper sides of the animal.

Dorso-ventral:

On the lower sides of the animal.

Eccentric:

Off-centre.

Ecology:

Study of the relationship among organisms and that to their physical surroundings.

Efferent:

Away from an organ (usually relates to blood vessels but also nerves) (cf. afferent).

Electrophoresis:

Process in which the relative movement of proteins is examined in an electric field.

Elliptical:

Oval or egg-shaped.

Elongate:

Of a long shape.

Endemic:

Found only in a particular geographical area.

Ephemeral:

Transitory, fleeting.

Epiphaunal:

Fauna on the surface.

Equivalve:

Two shell valves the same size and shape (cf. inequivalve) (bivalves).

Escutcheon:

A dorsal depression behind the umbones of a bivalve through which the ligament extends. Commonly with a smooth surface.

Estuarine:

Pertaining to an estuary, and commonly with brackish water.

Eulamellibranch:

A condition of bivalve gills where the gills are jointed by fleshy connections.

External fertilisation:

The union of a male and female gamete to form a zygote occurring outside the body of an animal typically in the water column.

Extinct:

No longer in existence, no longer living.

Eye spots:

Patches of pigment, sometimes sensitive to light, on the anterior end of an animal.

Faecal:

Pertaining to faeces.

Faeces:

Waste material excreted from the gut of an animal.

Family:

A rank in a taxonomic classification between an order and genus.

Fauna:

The entire animal life of a given region, habitat, or geological stratum.

Fertilisation:

The union of a male and a female gamete to form a zygote, sometimes referred generally to the act of insemination, impregnation or pollination.

Filibranch:

A condition of bivalve gills where the gills are jointed by ciliary connections.

Filter feeding:

Feeding where food is captured on the gills using the cilia on the gill filaments – commonly called ciliary feeding or suspension feeding.

Fissured:

Split or cracked.

Flagellum:

A whip-like structure on a cell. For single cells such as spermatozoa, it is the motile structure.

Flammulations:

Flame-like markings.

Fossil:

An organism, fragment, impression or trace of an organism preserved in a rock.

Freshwater:

Water with a salinity of less than 0.5 parts per thousand, or alternatively, less than 2 parts per thousand (seawater is commonly around 35 parts per thousand).

Fusiform:

Tapering at both ends; spindle-shaped.

Gastric caecum:

A caecum attached to the stomach.

Gastric shield:

A chitinous shield-like structure in the stomach.

Gastropod:

A member of the class Gastropoda.

Genus:

The rank in taxonomy above species level – each genus contains one or more species.

Gill:

A specialised respiratory surface. In molluscs, this is typically the ctenidium, however it may also be a secondary structure.

Glandular:

With glands.

Globose:

Rounded, globe-like.

Globular:

Rounded, globose.

Glochidium:

The parasitic, bivalved larva of unionoidean bivalves (including Hyriidae).

Gonoduct:

A duct transporting eggs or sperm.

Granulose:

Covered in granule-like pustules.

Growth lines:

Lines in the shell produced by incremental growth at shell edge.

Head:

The anterior section of an animal that bears the mouth and typically sensory structures.

Hermaphroditism:

Where both male and female reproductive organs are present in the same individual. Consecutive hermaphroditism is where the male and female organs do not occur in the individual at the same time, but successively. Simultaneous hermaphroditism occurs when the male and female reproductive organs occur in the individual at the same time.

Heterodont:

A hinge with two different types of teeth (cardinal and lateral).

Heterostrophic:

A condition where the protoconch is coiled in a different plane or different direction from the adult shell.

Hinge:

In bivalves this is the structure where the valves join and it consists of a ligament and, usually, interlocking hinge teeth.

Holotype:

The unique specimen on which a species name is based. The primary type or exemplar of a species.

Horny:

Made of horn-like organic material.

Host:

An organism which houses another organism such as a parasite or a commensal organism.

Hyperstrophic:

A gastropod with dextral anatomy but with a sinistrally coiled shell.

Hypobranchial gland:

A gland on the roof of the mantle cavity in many gastropods and some bivalves.

Imperforate:

An umbilicus is absent in a gastropod shell (cf. perforate).

Indirect development:

A larval stage is present in development.

Inequivalve:

Two shell valves of different size and/or shape (cf. equivalve) (bivalves).

Infaunal:

Animals occurring within the sediment.

Inner lip:

The part of the aperture that forms a lip on the inner (columellar) side.

Inner marginal teeth:

The innermost marginal teeth of the radula.

Internal fertilisation:

The union of a male and female to transfer sperm enabling the gametes to form a zygote inside the body of an animal.

Intertidal:

The part of the shore covered by high tide and uncovered at low tide.

Invaginated:

Folded inwards like the finger of a glove.

Invertebrate:

Animal without a backbone or spinal column.

Iridescent:

Showing a variety of colours when viewed from different angles.

Jaw:

The chitinous structure in the oral tube or outer part of the buccal cavity of gastropods – commonly primitively paired, but single (dorsal) in some.

Juvenile:

An organism not yet fully developed, with features of both the larval stage and the adult stage.

Karst:

Topography formed when rocks (typically limestone) are dissolved. Commonly rugged in shape.

Labial palps:

Two pairs of flap-like structures on either side of the mouth in bivalves.

Lamellae:

Raised thin ridges.

Laminate:

With laminae.

Larva:

Singular of larvae.

Larvae:

A developmental form of an organism, without adult characteristics and unable to reproduce.

Lateral:

From or on the side.

Lateral tooth:

A tooth that lies along the hinge line and is part of a heterodont hinge (see cardinal tooth). Or one or more radular teeth that lie next to the central teeth.

Lectotype:

A primary type selected from a syntype series (see syntype, holotype, paratype).

Lentic:

Still waters (as in lakes).

Lenticular:

Lens-shaped.

Ligament:

A resiliant but flexible organic structure that holds two valves together in a bivalve shell.

Limpet:

A cap-shaped shell – this type of shell morphology has been achieved convergently in many different gastropods and a few bivalves.

Lirae:

Spiral ridges or cords.

Lirate:

Ornamented with lirae.

Lobulated:

Forming lobes.

Lotic:

Flowing waters (as in streams or rivers).

Lunate:

Crescent-shaped.

Lunule:

A dorsal area in the front of the beak of some bivalve shells. It may be in the shape of a double crescent or heart-shaped.

Macrophytes:

Large aquatic plants (cf. algae).

Mantle:

A fold of skin (epidermis) covering the dorsal surface of the body of molluscs, including forming the roof of the mantle cavity (the space between the mantle and the body) that protects the gills. The outer surface of the mantle secretes the shell.

Marginal teeth:

The outermost teeth of a gastropod radula.

Marsupia:

Brood chamber in a bivalve gill where the bivalve parent is providing nutrients to the developing embryos.

Medial:

Middle, or towards the middle.

Mesocone:

The middle cusp or denticle on a radular tooth – equivalent to the main, median or central cusp.

Metapodial:

Relating to the metapodium.

Metapodium:

The main part of the foot of a gastropod (see propodium).

Microcostae:

Very fine costae (ridges).

Microsculpture:

Fine sculpture, often not visible in detail using an ordinary light microscope.

Molecular:

Relating to molecules – this term is often used for DNA (as in molecular analysis).

Monotypic:

Having only one type or representative, especially (of a genus) containing only one species.

Morphology:

The form and structure of an organism, with special emphasis on the external features.

Mucus:

The slimy substance secreted by goblet cells onto the surface of a mucus membrane to protect, lubricate and trap bacteria, dust, etc.

Multispiral:

Of several to many spirals or whorls (cf. paucispiral).

Nacre:

Mother of pearl – a special kind of iridescent shell layer.

Nephridium:

Kidney.

Neritiform:

Shaped like the marine genus Nerita.

Nerve ring:

The ring of ganglia and their connectives surrounding the buccal area or the oesophagus.

Omniphoric groove:

Groove on neck that runs on to the side of the foot from the mantle cavity.

Opercular pegs:

Pegs on the inner side of the operculum that provide additional surface for muscle attachment.

Operculum:

A horny or calcareous structure covering the shell aperture of a gastropod.

Opisthocline:

Leaning backwards relative to the coiling axis (cf. orthocline and prosocline).

Opisthogyrate:

Bivalve with beaks pointing posteriorly (cf. orthogyrate and prosogyrate).

Oral:

Pertaining to the mouth.

Order:

A rank in a classification between class and family.

Organic:

Pertaining to or derived from living organisms, or to compounds containing carbon as an essential component.

Orthocline:

Perpendicular relative to the coiling axis (cf. prosocline and opisthocline).

Orthogyrate:

Bivalve with beaks not pointing anteriorly or posteriorly (cf. opisthogyrate and prosogyrate).

Orthostrophic:

A normal coil.

Osphradium:

A chemosensory organ in the mantle cavity.

Outer lip:

The part of the aperture that forms a lip on the outer side.

Ovate:

An oval shape.

Oviduct:

A structure that transports eggs from the gonad to the exterior. In gastropods with internal fertilisation, the eggs are fertilised in the duct and surrounded by nutrients and a covering secreted from associated albumen and capsule glands before being released.

Oviparous:

Eggs are laid which develop outside the body of the parent.

Ovoid:

Of an oval shape.

Ovotestis:

A gonad that produces both sperm and eggs.

Ovoviviparous:

Similar to viviparous species where the eggs are internally fertilized and the young are born as larvae or juveniles, but differ in not obtaining nourishment from the parent other than by egg yolk.

Pallial:

Relating to the pallium (mantle) or to the pallial (mantle) cavity.

Pallial cavity:

Equivalent to mantle cavity.

Pallial line:

A line on the inner side of bivalve shells impressed by the pallial muscles.

Pallial tentacles:

Tentacles attached to the edge of the mantle.

Papilla:

Short finger-like structures (plural 'papillae').

Papillate:

With papillae.

Parasite:

Any organism that is intimately associated with, and metabolically dependent upon another living organism (the host) for completion of its life cycle, and which is typically detrimental to the host to a greater or lesser extent.

Paratype:

Secondary type(s) (see holotype).

Parietal:

In gastropods, this term is used for the area of the last whorl adjacent to the inner lip of the aperture.

Parthenogenesis:

The development of an organism from an unfertilised egg.

Parthenogenic:

A female that can produce eggs that develop as embryos without the involvement of a male.

Patelliform:

Limpet shaped (refers to the shape of the marine limpet Patella).

Paucispiral:

Of few spirals or whorls (cf. multispiral).

Pedal:

Relating to the foot.

Pedal slit:

A slit in the sole of the foot into which pedal glands open.

Penial:

Relating to the penis.

Penial lobe:

A non-glandular lobe on the penis.

Penis:

The male copulatory organ.

Penultimate:

Before the last – commonly used in relation to the second to last whorl of a gastropod.

Perforate:

Condition in which an umbilicus is present in a gastropod shell (cf. imperforate).

Pericardium:

A thin-walled chamber containing the heart.

Periostracal:

Pertaining to the periostracum.

Periostracum:

An organic layer on the outside of the shell. The periostracum may be thin and nearly invisible, thick, or in some species covered with hairs or other ornamentation.

Peripheral:

Pertaining to the periphery.

Periphery:

The edge of the whorl at the widest point (when used in context of the gastropod shell). Can also refer to the edge of a structure.

Peristome:

The edge of the aperture (or 'mouth') of a gastropod.

Phylum:

A rank in the hierarchy of classification that is immediately below kingdom.

Planate:

With a flat surface – used as a term to describe the flat dorsal side of some gastropods.

Planispiral:

Coiled in one plane (flat, with no spire).

Plicate gill:

A type of secondary gill convergent with a ctenidium in having structures that superficially resemble filaments.

Polymorphism:

Three or more forms of the same species. The most common form of polymorphism is different colour varieties.

Posterior:

The part of an animal that is towards the rear (i.e. that which follows when the animal is moving).

Praeputium:

The invertible sheath into which the penis retracts in many heterobranch gastropods.

Predator:

An organism that feeds by preying on other organisms, killing them for food.

Proboscis:

A retractable trunk-like snout that can invaginate. The mouth is at the anterior end of the extended proboscis.

Prodissoconch:

The larval or embryonic shell in a bivalve.

Propodial:

Relates to the propodium.

Propodium:

The anterior-most part of the foot of a gastropod.

Prosocline:

Leaning forwards relative to the coiling axis (cf. orthocline and opisthocline).

Prosogyrate:

Bivalve with beaks pointing anteriorly (cf. orthogyrate and opisthogyrate).

Prostate gland:

A gland in the male genital tract.

Prostatic duct:

A duct of the prostate gland.

Protandrous:

Hermaphrodite that first develops as male and then becomes female.

Protoconch:

The larval or embryonic shell in a gastropod (cf. teleoconch).

Protostyle:

A rotating mucoid rod that lies in the style sac.

Proximal:

Situated near the centre of the body or point of attachment (cf. distal).

Pseudocardinal:

The hinge teeth of some unionoidean bivalves that are short and close to the umbones, and resemble the cardinal teeth of heterodont bivalves.

Pulmonary cavity:

A modified mantle cavity which in pulmonates functions as a lung.

Pupiform:

Shaped like members of the land snail family Pupillidae.

Pupoid:

Shaped like Pupa, a small, bullet-shaped land snail.

Pustule:

Small raised, rounded spots.

Pustulose:

Covered with pustules.

Pyriform:

Pear-shaped.

Quadrate:

Approximately square or rectangular.

Radula:

An anatomical structure that is used by molluscs for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, typically used for scraping or cutting food. Absent in bivalves and a few gastropods.

Rectal:

Relating to the rectum.

Rectum:

Distal section of the gut, after the intestine. It opens at the anus.

Renal gland:

A gland-like structure in the kidney.

Reticulate:

Of net-like appearance.

Retractor:

A muscle that, when it contracts, withdraws a structure.

Rhachidian:

An alternative name for the central radular teeth.

Rhachis:

Main axis of shaft.

Rhomboid:

Rhombus-shaped (i.e., a flat shape with four equal straight sides, for example diamond-shaped).

Rotund:

Fat, rounded.

Rudimentary:

Reduced, hardly present (similar to vestigial).

Rugae:

Ridges.

Rugose:

Of rough texture.

Salivary gland:

Mucus- or, less commonly, enzyme-producing glands that open into the buccal cavity.

Sarcobelum:

The structure forming the tip of the everted preputium, through which the penis passes in copulation.

Scalloped:

An undulating edge or fluted edge.

Schizodont:

The type of hinge seen in unionoidean bivalves, and in the marine Trigoniidae.

Sediment:

Particulate matter that has been transported by wind, water or ice and subsequently deposited, or that has been precipitated from water.

Segmentation:

The division of a body or appendage into a linear sequence of similar units.

Seminal receptacle:

A sperm sac in which sperm is stored after copulation.

Seminal vesicle:

A swelling or pocket in the vas deferens of the male in which sperm is stored.

Setae:

Stiff, minute hair-like structures.

Sexual dimorphism:

When males and females differ in shape and/or size.

Shell:

The hard outer covering of a wide variety of invertebrates and notably molluscs. Mollusc shells are mineralised with calcium carbonate (CaCO₃).

Shouldered:

Relating to gastropod whorls – where there is a flattened area on the upper part of the whorl.

Sinistral:

Coiled to the left (cf. dextral).

Sinkhole:

A (typically large) hole in the ground (commonly in limestone).

Sinuate:

See sinuous.

Sinuous:

Winding, with few to many bends.

Siphon:

Canal or tube in molluscs (may occur in both animal and shell). The siphon in neogastropods is used to draw water into the mantle cavity.

Spatulate:

Spatula or spoon-like.

Species:

A group of organisms (or other entities) distinct from other groups. Also a taxon of the rank of species in biological classification that is the category below genus. Used in this latter sense, it is the basic unit of biological classification.

Sperm sac:

A sac containing sperm in the female system.

Spermathecal duct:

The duct of the spermathecal gland.

Spermathecal gland:

A sperm sac in the female system which receives sperm during copulation. Equivalent to the bursa copulatrix but this term is usually used in euthyneuran heterobranchs.

Spermatophore:

A packet containing sperm that is passed from male to female in some molluscs.

Spire:

The raised, tapering portion of many gastropod shells.

Striae:

Fine axial or spiral threads or grooves.

Style sac:

The sac-like extension of the stomach in which the crystalline style or protostyle is contained.

Stylet:

A sharply pointed, slender structure. Present as a terminal process in some gastropod penes (penial stylet).

Subangled:

Weakly angled.

Subcentral:

Near central.

Subobsolete:

Almost gone, or almost absent.

Subpupiform:

Somewhat resembling a pupiform shape.

Substratum:

The sediment, surface or medium to which an organism is attached or upon which it grows, substratum.

Subterminal:

Near terminal.

Subtrochiform:

Somewhat trochiform in shape.

Subumbonal:

Near the umbone.

Supra-anal:

Above the anus.

Supra-pedal:

Above the foot.

Suspension feeder:

See filter feeder.

Suture:

The point where the whorls join on a gastropod shell.

Symbiosis:

A long-term relationship between two species - can be commensal, parasitic or mutualistic.

Sympatric:

Two or more species living in the same location (cf. allopatric).

Sympatry:

See sympatric.

Syntype:

The original type series when a holotype was not designated.

Taenioglossate:

A radular configuration of seven teeth in each row.

Taxa:

Pleural of taxon.

Taxon:

Any taxonomic entity (species, genus, family, phylum etc.).

Taxonomy:

The theory and practice of describing, naming and classifying organisms (also referred to as systematics).

Teleoconch:

The ‘adult’ whorls of a gastropod shell (cf. protoconch).

Tentacle:

Appendages associated with the head-foot. Cephalic tentacles are found on the head.

Tricuspid:

With three cusps.

Trochiform:

Shaped like the marine genus Trochus.

Truncate:

Shortened or cut off.

Turbinate:

Shaped like the marine genus Turbo.

Umbilicate:

With an umbilicus.

Umbilicus:

An opening in the base of a gastropod shell. It is a hollow often cone-shaped space that is located within the coils of the shell.

Umbo:

The umbo (plural umbones) is the highest (usually protruding) part of each of the two valves making up a bivalve shell - it represents the earliest part of the shell.

Umbonal:

Relating to the umbo.

Uniramous:

A single arm-like structure.

Unsegmented:

Without articulation.

Vagina:

The terminal part of the female reproductive system in euthyneruans.

Vaginal pouch:

A pouch associated with the vagina.

Varices:

Thickened rib-like structures on the outer surface of a gastropod shell. Apertural varices lie near of just behind the outer lip of the aperture. Such varices may be left on the shell surface as the shell grows.

Varicose:

With varices.

Varix:

See varices.

Vas deferens:

A tube carrying the sperm from the testis to the penis in the male.

Vector:

A species harboring a parasite and which is capable of passing on the parasite on to other hosts.

Veliger:

The shelled swiming larva of gastropods and bivalves.

Ventral:

Describing the surface of an animal that is nearest or next to the ground or other support.