Glossary of Morphological and Anatomical Terms

labiate - Exaggerated marginate foramen in which dorsal edge is prolonged and liplike.
lacuna - Aperture in hood.
lamella - Sheetlike extension of primary and even underlying secondary shell deposited by retractilemantle margin on external shell surface (see growthlamella); also used for calcareous ribbon comprisingspiralium and coiled extension from arm of jugum.
lamellar layer - See primary layer secondary layer.
lamina - Parallel-sided, thin mineral constituents of ashell succession, normally ensheathed in membranes and consisting of tablets, plates, or blades in various stages of amalgamation.Fig.247.
laqueiform - Long reflected loop with laterovertical connecting bands connecting ascending anddescending lamellae, and lateral connecting bandsextending between descending lamellae and medianseptum.
lateral adductor muscles - Paired muscles in thecideidines attached posterolaterally in ventral valve and on either side of cardinal process of brachial valves.
lateral areas - Ventral palintrope on either side of delthyrial structures.
lateral branch - Part of jugum continuous with primary lamella.Fig.336.
lateral cavities - See umbonal chambers.
lateral connecting bands - See connecting bands.
lateral oblique muscles - Paired muscles in some inarticulated brachiopods, originating on ventral valve anterolaterally of posterior adductor muscles and passing anterodorsally to insertions either on dorsal valve and anterior body wall against anterior adductors (discinids) or entirely on anterior body wall (craniids).Fig.374.
lateral ridges - Ridges of secondary shell common in productines, extending laterally from cardinal process or ventral beak diverging from posterior margin toward ears or lateral margins.
lateral septa - See anderidia.
lateral slopes - Valve surfaces on either side of median sector of shell.
laterovertical - Long reflected loop typical of adult Pictothyris, with laterovertical connecting bands only.
leiolophid stage - Rudimentary lophophore ring before development of tentacular appendages.
lemniscate - Saclike gonocoel giving rise to branches that extend to posterolateral margins with corresponding peripheral reduction of vascula media and vascula myaria.Fig.380.
length - Distance from most posterior point of valve (normally umbo) to farthest point on anterior margin measured on commissural plane in plane of symmetry or parallel with it.Fig.283.
lenticular stage - Both valves gently and subequally biconvex anterior margin rectimarginate.
ligate stage - See lobate.
limbus - Flattened inner margin of inarticulate valve.
linguiform extension - Anterior tongue-shaped extension of either valve.
liothyrinid stage - See lenticular stage.
lirae - Fine concentric or radial ridges and grooves.
listrium - Plate in some discinids closing anterior end of pedicle opening that has migrated posteriorly.Fig.286.
lobate - Opposite folding with single sinus in one valve opposed by single sulcus in other; commissure rectimarginate.Fig.288.
long loop - See loop.
longitudinal axis - Intersection of planes of commissure and symmetry.Fig.283.
loop - Support for lophophore composed of secondary shell and brachiotest extending anteriorly from crura as closed apparatus that may be short (centronellidines, terebratulidines) or long (terebratellidines) or a derivative of one of these forms.Fig.338.
lophidium - Inverted V-shaped projection of median posterior part of dorsal valve or of external face of cardinal process helping to close gap in delthyrium in some aulostegoids.
lophophore - Feeding and respiratory organ with tentacles, symmetrically disposed around mouth, typically suspended from anterior body wall but may be attached to dorsal mantle occupies mantle cavity.Fig.1.
lophophore platform - See brachial platform.
lophrothyrid stage - See uniplicate.