GLOSSARY

• ADDUCTOR MUSCLES: The paired muscles which, on contraction, close the shell. Each is commonly divided dorsally into anterior and posterior elements.
• BODY CAVITY: The posterior coelomic region between the two valves, enclosed by epithelium, containing the body organs; digestive system, muscles, metanephridia, etc.
• BRACHIAL CAVITY: The anterior space between the valves, lined by mantle and body-wall epithelium, containing the lophophore.
• BRACHIAL LOOP: Delicate, shelly, loop-like support for the lophophore extending anteriorly from the crura. There may be a supporting median septum.
  
• CAECA (sing. CAECUM): Outgrowths of the outer mantle epithelium contained in the endopunctae of the shell substance.
• CARDINAL PROCESS: Postero-median area of attachment of the diductor muscles in the dorsal valve, commonly a bilobed boss of shell.
  
• COMMISSURE: The line of junction between the edges of two valves.
• CRURA (sing. CRUS): Shelly processes extending forwards from the socket region of the dorsal valve, giving support posteriorly to the lophophore. The distal ends may be prolonged into a brachial loop supporting much of the lophophore.
  
• CRURAL PLATES: Shelly plates extending medianly from the crura, sometimes fusing to the floor of the dorsal valve.
• DELTHYRIUM: Median triangular aperture in the margin of the ventral valve, wholly or partially used as the pedicle aperture.
• DELTIDIAL PLATES: Pair of shelly plates, growing medianly from the delthyrial margins, constricting the pedicle aperture.
• DENTAL PLATES: Shelly walls supporting the teeth from the floor of the ventral valve.
• DIDUCTOR MUSCLES: The paired muscles which, on contraction, open the shell by pulling on the cardinal process, situated on the opposite side of the hinge axis from the ventral areas of attachment.
• DIGESTIVE DIVERTICULA: Large secretory organ, assisting in the digestion of food, more or less surrounding the stomach and with ducts openiong to the stomach.
• ENDOPUNCTATE: The shell condition in which minute canals (ENDOPUNCTAE sing. ENDOPUNCTA) extend from the inner valve surface almost to the exterior. In life these endopunctae accommodate prolongations of outer mantle epithelium (CAECA).
• ENTERIC GANGLIA: The principal nerve centre of the brachiopod body, consisting of a ring of nerves with swollen regions (GANGLIA sing. GANGLION) surrounding the oesophagus. Nerves lead from this to various parts of the body.
• FOOD GROOVE: The canal along the inner side of the lophophore along which food is transported to the postero-medianly positioned mouth.
• "HEART": Small, thin-walled contractile organs situated close to the stomach, thought to assist in the circulation of coecolomic fluid.
• HINGE AXIS: The line joining the points of articulation, the teeth, about which the valves rotate when opening and closing.
• HINGE PLATES: A general term, including crural plates, for skeletal structures connected with the sockets and crura in the dorsal valve.
• IMPUNCTATE: Shell lacking either endopunctae or pseudopuncteae.
• INTESTINE: That part of the digestive system beyond the stomach ending at the anus, in inarticulates, and blindly in the articulates.
• LOPHOPHORE: Filamentous, commonly coiled, feeding organ symmetrically disposed about the mouth and occupying the brachial cavity. Within it are coelomic cavitiesand, at the base of the filaments, the food groove leads to the postero-medianly positioned mouth.
• LLOP or BRACHIAL LOOP: Delicate shelly loop-like support for the lophophore extending anteriorly from the crura.
• MANTLE: Folds of ectodermal epithelium, extending forwards from the body wall, which line the brachial cavity and secrete shell tissue.
• MANTLE CANALS: Canals in the mantle epithelium radiating from the body cavity.
• MEDIAN SEPTUM: A vertically disposed shell plate of variable height or length in the median plane of either valve, normally present in the body cavity.
• METANEPHRIDIA: The principal excretory organs. Normally a single pair (but rhynchonelloids have two pairs) situated in the body and connected by short ducts to openings in the body wall leading into the brachial cavity. They serve also as the openings through which eggs and sperm are ejected.
• MOSAIC: The pattern on the internal surfaces of valves formed by the margins of microscopic shell units in the secondary layer.
• PEDICLE: Cuticle-covered stalk, commonly protruding from the ventral valve, attaching the animal to the sea floor, and controlled by muscles.
• PEDICLE APERTURE: The aperture, normally confined to the ventral valve, through which the pedicle extends. This aperture is within the delthyrium, but may be restricted in size by the growth of the deltidial plates.
• PEDICLE ADJUSTOR MUSCLES: The muscles, commonly at least four, attached to the base of the pedicle which control the movement of the shell around its attached pedicle. In some species the muscles there assist in shell articulation.
• PERIOSTRACUM: The thin organic layer on the exterior of the shell.
• PROTEGULUM: The first-formed valves secreted by the juvenile brachiopod and commonly distinguished from later shell by the absence of ornamentation.
• PSEUDOPUNCTATE: The shell condition of having PSEUDOPUNCTAE (sing. PSEUDOPUNCTA), which are conical flexures in the lamellose shell of many fossil brachiopods forming rod-like structures superficially resembling endopunctae.
• PUSTULE: Small nodose protuberance forming part of the external ornamentation of the shell.. When larger they are called tubercules.
• RIBS: A form of external ornamentation in which the shell suface is radially ridged. Very fine radial ridges are called striations.
• SHELL MOSAIC: (see MOSAIC).
• SOCKETS: A pair of cavities, near the posterior margin of the dorsal valve, into which the teeth fit.
• SPICULES: Variably shaped calcareous plates within, and helping to support, the mantle and lophophore epithelia in some species.
• SOCKET RIDGES: Ridges of shell, extending antero-laterally from the cardinal process, bordering the inner side of the tooth sockets on the dorsal valves.
• TEETH (hinge teeth): The two principal articulatory processes, situated on the ventral valve at the antero-lateral margins of the delthyrium.
• TUBERCULES: Large nodose protuberances on the shell surfaces (see PUSTULES).
• UMBO: Median, apical posterior region of either valve.
• VALVE: One of the two skeletal coverings of the brachiopod, together consituting the shell. These are entirely calcareous in articulates and calcareous or chitinophospatic in the inarticulates.
  
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