Glossary of Morphological and Anatomical Terms
accessory denticles - See denticles.
accessory diductor muscles - Pair of muscles branching posteroventrally from main diductor muscles and inserted in ventral valve posterior to adductor bases.Fig.348.
accessory lamellae - Pair of lamellae developed from arms of jugum and coiled parallel to main lamellae of spiralia.Fig.336.
accessory septum - Used informally for any septum ancillary to others.
accessory socket - Outer part of divided dental socket of plectambonitoids; also used for depression in outer socket ridge.Fig.322,Fig.323.
accessory tooth - Articulating process flanking hinge tooth of plectambonitoids and fitting into accessory socket in dorsal valve.Fig.323.
adductor muscles - Muscles that contract to close shell.
adductor pits - Pair of depressions indenting anterior face of notothyrial platform of some orthides for attachment of posterior adductor muscles.
adjustor muscles - Two pairs of muscles in many articulated brachiopods moving pedicle or shell and arising from proximal end of pedicle to attach posterolaterally of diductors in the ventral valve (pedicle adjustors) and on hinge plates or floor of dorsal valve behind posterior adductors (brachial adjustors).Fig.348,Fig.349.
adminicula - Paired subvertical plates situated umbonally in either valve and extending from valve floor to ventral edges of dental flanges (ventral adminicula) or to dorsal edges of crural bases (dorsal adminicula however, see crural plates).Fig.324_3.
alae - Winglike extensions at cardinal extremities.
alate plate - Flaplike extension of secondary shell arising from lateral surface of brachiophore plate inporambonitoids.Fig.366.
alternate folding - Deflection of shell surface in whichfold of one valve is opposed by sulcus of other.Fig.289.
alveolus - See cardinal process pit.
ancilliary strut - Secondary shell material depositedbetween brachiophore base and median ridge insome orthides.
anderidia - Paired ridges in somestrophomenides, situated posterolaterally of medianplane of dorsal valve of increasing elevation or projecting anterolaterally.Fig.361.
angle of spines - External angle subtended by chonetoid external hinge spines with posterior margin ofventral valve, measured in plane parallel with planeof commissure.
anterior - Direction in plane of symmetry or parallel to it away from pedicle and toward mantle cavity.Fig.283.
anterior lateral oblique muscles - Pair of muscles insome lingulids originating on ventral valve posterolateral to central muscles converging dorsally totheir insertions anteriorly on dorsal valve.Fig.346_2.
antiplicate - See biplicate.
antron - Triangular to elongate groove variably developed between cardinal process buttress plates andbreviseptum in some productides.
antygidium - Low, platelike ridge of shell near beak ofdorsal valve, covered externally by cuticle and deposited during ventral migration of junction ofpedicle epithelium with outer epithelium.Fig.319_3.
anvil-type fiber - A fiber of the secondary shell with theconvex surfaces of the anvil-like cross section facingthe valve interior.Fig.242.
apex - First-formed part of valve around which shell hasgrown subsequently (term usually restricted tovalves having this point placed centrally or subcentrally).
apical angle - Angle subtended by umbonal slopes atumbo.
apical callosity - See pedicle callist for inarticulatedbrachiopods, see apical process.
apical cavity - Undivided space beneath umbo in eithervalve.
apical plate - Dorsally enlarged pedicle collar partly closing apex of delthyrium.
apical process - Variably shaped protuberance in umbonal region of ventral valve of some acrotretoids, which probably served as a muscle platform and may have contained a pedicle tube.Fig.346,Fig.378.
apicate - Beak of ventral valve with a subapical hypothyrid or amphithyrid foramen.
apocopate - Dorsal, mantle-canal system with single pair of canals in addition to vascula genitalia.Fig.381.
arcuiform - Crura hammer shaped in cross section, with arcuate heads concave toward each other.
area - See cardinal area.
arms of jugum - Processes arising by bifurcation of distal end of jugal stem which may become extended into accessory lamellae.Fig.336.
articulation - Interlocking of two valves by projections along their posterior margins; commonly effected in articulated brachiopods by two ventral teeth fitting sockets of dorsal valve but may be assisted or replaced by other projections and complementary pits.Fig.322.
ascending lamellae - Paired ventral elements of long terebratelloid loop continuous anteriorly with ventrally recurved descending lamellae and joined posteriorly by transverse band.Fig.338.
attrite - Ends of beak ridges worn away.
aulacoterma - Thickening on inside wall of richthofeniid ventral valve against which dorsal valve rests when shell is closed.
auriculate - Opening bounded by deltidial plates bearing external rims or winglike extensions.
axial - Phase of loop development with a vertical plate (Paleozoic forms) or septal pillar (post-Paleozoic forms); descending lamellae complete in Paleozoic forms, rudimentary in most post-Paleozoic forms.
