Phylum Brachipopoda

MORPHOLOGY 

Images taken and/or modified from (moving left to right) Williams and Rowell, 1965a and Williams et. al., 1997a (combined picture), Williams and Rowell, 1965b, Shrock and Twenhofel, 1953, Williams et. al., 1997b.

The following diagrams and sketches display some important brachiopod morphology.

TERMINOLOGY 

Definitions of terms from Williams and Brunton, 1997.

Acuminate Phase in loop (support for lophophore consisting of secondary shell material) development with laterally bowed, descending lamellae extending from crura but otherwise unsupported and uniting anteromedially to form an echmidium (spear shaped plate formed in the ontogeny of loop in Paleozoic terebratulid brachiopods).
Adductor muscles Muscles that contract to close shell. Inarticulated brachiopods two adductor muscles, each divided dorsally, are commonly present to produce single pair of scars located between diductor (muscles that open the shell) impressions in ventral valve and two pairs (anterior, posterior) in dorsal valve. In inarticulated brachiopods two pairs of adductor muscles (anterior, posterior) are commonly present, passing almost directly dorsoventrally between valves.
Alate Having winglike extensions at cardinal extremities.
Anacline  see inclination of cardinal area or of pseudointerarea
Apex  First formed part of valve around which shell has grown subsequently (term usually restricted to valves having this point placed centrally or subcentrally).
Apsacline see inclination of cardinal area or of pseudointerarea
Auriculate  Opening bounded by deltidial plates bearing external rims or winglike extensions.
Beak  Extremity of umbo (apical portion of either valve), commonly pointed.
Biconvex  Both valves convex.
Bifurcate  Lophophore support in form of Y-shaped median septum.
Brachial valve  See dorsal valve.
Brachiophores  Blades of secondary shell projecting from either side of notothyrium (opening bisecting dorsal cardinal area or pseudointerarea) and forming or in close association with inner socket ridges.
Capillate  Having very fine radial ridge on outer surface of shell.
Cardinal angles  Angle between hinge line and posterolateral margins of shell.
Cardinal process  Blade or variably shaped boss of secondary shell situated medially in posterior end of dorsal valve and serving for separation or attachment of paired diductor muscles (muscles that open valves).
Chilidium  Crescentic plate covering apex of notothyrium (opening bisecting dorsal cardinal area or pseudointerarea), commonly convex externally and extending for variable distances ventrally over proximal end of cardinal process and chilidial plates when present.
Commissure  Line of junction between edges or margins of valves.
Concavoconvex  Dorsal valve concave; ventral valve convex.
Convexoconcave Dorsal valve convex; ventral valve ventral valve concave.
Convexoplane Dorsal valve convex; ventral valve plane.
Costa (pl., costae) First formed radial ridge on external surface of shell most commonly originating at the junction between the brephic and neanic shell (juvenile stages of growth development). [Also but ambiguously used for any coarse rib, without reference to origin. Costella is a fine rib, amd capilla is a very fine rib. This usage gives no indication of the nature of radial ornamentation and any quantitative definitions, related to the incidence of ribs at the margins of shell irrespective of their sizes, are of no value. Thus in brachiopods ornamented by ribs that increase in wave length during growth, shells of the same species could be described as capillate, costellate, or costate according to their size.]
Costate  Shell radially ornamented exclusively by costae.
Costella (pl., costellae)  Radial ridge on external surface of shell originating later than costa bifurcation of existing costa or costella or by intercalation between earlier-formed ribs.
Costellate  Having costellae.
Crenulations  Small, protruding ridges that alternate with complementary sockets located along cardinal margin or hinge line of both valves; also small processes on posterior surfaces of dental sockets fitting into accessory sockets in hinge teeth.
Crura  Paired processes extending from cardinalia (structures of secondary shell in posteromedian region of dorsal valve that deal with support of lophophore, muscle attachment, and articulation) or septum to give support to posterior end of lophophore; distal ends may also be prolonged into primary lamellae of spire or descending lamellae of loop.
Crural bases  Parts of crura united to hinge plates or socket plates and separating inner and outer hinge plates when present.
Crural pits  Cavity near floor of dorsal valve separating brachiophore plate (basal part of brachiophore that join floor of valve) and fulcral plate in some orthides.
Crural plates  Plate extending from inner edge of outer hinge plate or crural base to floor of dorsal valve; may fuse medially with counterpart to form septalium.
Cynocephalous  Sharply folded dorsal valve.
Deltidial plates  Two plates growing medially from margins of delthyruim (aperture bisecting ventral cardinal area or pseudointerarea, commonly serving as pedicle opening), partly or completely closing it.
Dental cavities  Anteriorly expanding cavity, presumably occupied by evagination of outer epithelium secreting the tooth of some atrypoids.
Dental lamellae  See dental plates.
Dental plates  Variably disposed plates of secondary shell underlying hinge teeth and extending to floor of ventral valve.
Dorsal valve  Valve that invariably contains any skeletal support for lophophore and never wholly accommodates pedicle; commonly smaller than ventral valve and with distinctive muscle-scar pattern.
Dorsibiconvex  Dorsal valve more convex than ventral valve.
False area  Previously used for any poorly defined cardinal area or pseudointerarea.
Filum (pl., fila)  Fine concentric ridge of variable persistence ornamenting external surface of shell.
Fold  Major elevation of valve surface, externally convex in transverse profile and radial from umbo.
Fulcral plates  Small plate raised above floor of dorsal valve extending between posterior margin and brachiophore plate (basal part of brachiophore that join floor of valve) or inner socket ridge and socket plate and forming floor of socket.
Geniculate  Abrupt and more or less persistent change in direction of valve growth producing angular to sharply rounded bend in lateral profile.
Gibbous A prominent swelling to one side.
Growth lines  Concentric line on outer surface of shell formed when forward growth of shell temporarily ceased.
Hinge line  Straight posterior margin of shell parallel with hinge axis; previously used as synonym of cardinal margin.
Hinge teeth  Two principle articulating processes situated at anterolateral margins of delthyrium (aperture bisecting ventral cardinal area or pseudointerarea, commonly serving as pedicle opening) and articulating with dental sockets in dorsal valve.
Hypercline  See inclination of cardinal area or of pseudointerarea.
Inclination of cardinal area or of pseudointerarea  Commonly used terms to describe the condition of either valve based on convention of viewing specimen in lateral profile with beaks to left and dorsal valve uppermost, referring cardinal area to its position within one of four quadrants defined by commissure plane and plane normal to it and symmetry plane, touching base of cardinal areas. Cardinal area lying on continuation of commissure plane is orthocline. Moving clockwise, cardinal area in first quadrant is weakly to strongly apsacline; at 90 degrees to orthocline it is catacline; and continuing counterclockwise into bottom right quadrant cardinal area is weakly to strongly procline.
Jugum  Medially placed structure of secondary shell connecting two primary lamellae of spiralia.
Lamella (pl., lamellae)  Sheetlike extension of primary and even underlying secondary shell deposited by retractile mantle (prolongation of body wall, secretes shell) margin on external shell surface; also used for calcareous ribbon comprising spiralium and coiled extension of arm of jugum.
Lamellose  Having lamellae.
Listrium  Plate in some discinids closing anterior end of pedicle opening that has migrated posteriorly.
Lophophore  Feeding and respiratory organ with tentacles, symmetrically disposed around mouth, typically suspended from anterior body wall but may be attached to dorsal mantle (prolongation of body wall, secretes shell); occupies mantle cavity (anterior space between valves bounded by mantle and anterior body wall).
Muscle field  Area of valve in which muscle scars are concentrated.
Muscle scars  More or less well-defined impression or elevation on valve representing final site of attachment of muscle.
Myophore  Differentiated site of diductor muscle attachment on cardinal process, consisting of ridged myotest (muscle scar shell).
Oblique muscle  Variable sets of muscles in inarticulated brachiopods responsible for rotational and longitudinal movements of valves.
Orthocline - See inclination of cardinal area or of pseudointerarea.
Parvicostellate  Costellae numerous, arising entirely by intercalation between widely spaced costae.
Pedicle  Variably developed, cuticle-covered, stalklike appendage commonly protruding from ventral valve that adjusts position of shell relative to external environment.
Pedicle foramen  Subcircular to circular perforation of shell through which pedicle passes.
Pedicle groove  Subrectangular groove dividing ventral pseudointerarea medially and affording passage for pedicle in many lingulides.
Pedicle notch  Small, subtriangular depression, posteromedially placed on limbus (flattened inner margin of inarticulate valve) of paterulids, probably functioning as pedicle groove.
Pedicle opening  Variably shaped aperture in shell through which pedicle emerges.
Pedicle tube  Internally directed tube of secondary shell continuous with margin of pedicle foramen and enclosing proximal part of pedicle.
Pedicle valve  See ventral valve.
Planoconvex  Dorsal valve flat; ventral valve convex.
Plication  Major undulation of commissure, reflected on shell interior, with crest directed dorsally; commonly but not invariably associated with dorsal fold and ventral sulcus.
Propareas  Pair of subtriangular halves of psuedointerarea divided medially by various structures of inarticulated brachiopods.
Psuedodeltidium  Single, convex, or flat plate affording variability complete cover of delthyrium (aperture bisecting ventral cardinal area or pseudointerarea, commonly serving as pedicle opening) but invariably closing apical angle when foramen is supra-apical or absent and always dorsally enclosing apical foramen.
Pseudointerarea  Somewhat flattened, posterior sector of shell of some inarticulated brachiopods secreted by posterior sector of mantle (prolongation of body wall, secretes shell) not fused with that of opposite valve.
Puncta (pl., punctae)  Perforation penetrating shell to connect with periostracum (organic external layer of shell) and occupied by caecum as in cranioids; any perforation apparently penetrating fossil shell and large enough to accommodate caecum.
Punctate  Having punctae.
Quincuncial (quincunx arrangement)  An arrangement of five punctae with one at each corner of a rectangle or square and one at the center.
Raduliform  Hook shaped or rodlike crura that arise on ventral side of hinge plate and project toward ventral valve.
Rectimarginate  Having planar anterior commissure.
Ruga (pl., rugae)  Concentric or oblique wrinkling of external shell surface.
Septalium  Troughlike structure of dorsal valve between crural bases, consisting of crural plates (or homologues) fused medially and usually supported by median septum, but may be unsupported or sessile; does not carry adductor muscles. See crural plates.
Septum (pl., septa)  Relatively long, narrow elevation of secondary shell, commonly bladelike; indicated within underlying floor of valve by persistent high, narrow deflections of shell fabric originating near primary layer (outer , mineralized shell layer beneath the exterior organic layer).
Sinus  Major undulation of commissure with crest directed ventrally, commonly but not invariably associated with ventral fold and dorsal sulcus; also used irrespective of commissure, as a synonym of sulcus.
Socket  Excavations in posterior margin of dorsal valve for reception of hinge teeth.
Socket plate  Pair of plates supporting inner socket ridges, attached to cardinal process, and resting ton floor of dorsal valve of orthotetoids and some orthoids; also pair of plates defining sockets of atrypid dorsal valve, confined by iner socket ridges medially and normally supported by thickened shell deposit.
Socket ridge  Linear elevations of secondary shell extending laterally from cardinal process and bounding anteromedian margin of dental sockets.
Spiralia  Pair of spirally coiled lamellae composed of secondary shell and supporting lophophore.
Spiralophous  Having lophophore in which brachia are spirally coiled and bear single row of paired tentacles.
Striae  Fine grooves or incisions.
Sulcate  Form of alternate folding with dorsal valve bearing median sulcus and anterior commissure median sinus.
Sulcus  Major depression of valve surface, externally concave in transverse profile and radial from umbo (apical portion of either valve containing the beak).
Truncated  Ventral umbo (apical portion of either valve containing beak) or articulated brachiopods with beak abraded due to pedicle movement and foramen in transapical position.
Umbonal muscle scar  Scar left by single muscle occurring in some lingulides, thought to be homologous with posterior adductors; consists of two bundles of fibers posteriorly and slightly asymmetrically placed.
Uniplicate  Form of alternate folding with ventral valve bearing median sulcus and anterior commissure median plica (plication).
Valve  One of two separate halves that make up the brachiopod shell.
Vascula media  Pair of mantle (prolongation of body wall, secretes shell) canals in either valve, medially located, projecting anteriorly from body wall.
Ventral valve  Valve through which pedicle commonly emerges, usually larger than the dorsal valve and invariably containing teeth when present.
Ventribiconvex  Both valves convex, ventral valve more strongly so than dorsal.
Visceral area  Part of shell enclosing body cavity.