#  Phylum Brachipopoda 

 



 ##  

  expand\_more  

 
  

 

#### 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.

   ![anatomy](/sites/g/files/omnuum8411/files/styles/hwp_1_1__360x360_scale/public/trenton/files/brachanatomy.jpg?itok=42Mf12mh) 

 

Brachiopod anatomy and muscle arrangement based on (top) Terebratulina and (bottom) Calloria inconspicua   ![symmetry](/sites/g/files/omnuum8411/files/styles/hwp_1_1__360x360_scale/public/trenton/files/brachsymmetry.jpg?itok=PHbMGxoi) 

 

External features and symmetry (1 posterior view, 2 left lateral, 3 dorsal, 4 dorserolateral)   ![convextity](/sites/g/files/omnuum8411/files/styles/hwp_1_1__360x360_scale/public/trenton/files/brachconvexity.jpg?itok=WsK1pvSG) 

 

Different forms of convexity for Brachiopod shells.  
brachlophophores   ![brachlophophores](/sites/g/files/omnuum8411/files/styles/hwp_1_1__360x360_scale/public/trenton/files/brachlophophores.jpg?itok=Wr_di6gv) 

 

Various shapes of Spiralia (1 a spiriferid, 2 Protozyga, 3 a zygospirid, 4 a koninckinid with apices directed ventrally, 5 an atrypid with apices directed dorsally)#### 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 plate**s 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.