Glossary of Morphological and Anatomical Terms

magellaniform - Type of free terebratellide loop consisting of long descending lamellae recurved into ascending lamellae that meet in transverse band.

magelliform - See haptoid.

main flanks - See lateral slopes.

maniculiform - Derived from raduliform type, with handlike processes at end of straight, ventrally directed crura.

mantle - Prolongation of body wall as fold of ectodermal epithelium.Fig.1.

mantle canals - Flattened, tubelike extensions of body cavity into mantle.Fig.379.

mantle cavity - Anterior space between valves bounded by mantle and anterior body wall and containing lophophore.Fig.1.

mantle papilla - See caecum.

mantle sinus - See mantle canal.

margin - Edge of valve.

marginal flange - See subperipheral rim.

marginal ridge - See subperipheral rim.

marginal spines - Long, slender prolongations of interspaces between ribs of rhynchonellides lying against inner surface of opposing valve when shell is shut and forming grille when shell is open; also used for spinose extensions of growth lamellae.Fig.300.

marginate - Pedicle foramen with thickened margin.

marsupial notch - Small double notch or perforation in ventral edge of brachial bridge in some adult female thecideoids marking passage of two specialized posteriorly directed filaments to which embryos are attached.

median - In plane of shell symmetry.Fig.283.

median buttress - Knoblike projection at posterior end of dorsal median septum in some acrotretoids, which may have been the site of attachment of umbonal muscle.Fig.378.

median partition - Median septum supporting anterior part of trimerelloid muscle platform and dividing cavity beneath platform into two vaults.Fig.375.

median plane - See plane of symmetry.Fig.283.

mediotest - Variably persistent, granular sheet occurring medially in platelike structures of fibrous secondary shell.

mediovertical - Long reflected loop typical of adult Ecnomiosa with a pair of mediovertical connecting bands extending from the median septum to the transverse band.

megathyrid - Posterior margin long and straight.

megerliiform - Loop of kraussinids with descending lamellae united to anterior projections of Yshaped median septum extremities of median septum also united by narrow transverse band.

mergiform - Variant of raduliform type with long, closely parallel crura arising directly from swollen edge of dorsal median septum.

mesothyrid - Pedicle opening located partly in ventral umbo and partly in delthyrium beak ridges appearing to bisect foramen.Fig.318.

metacarinate stage - See bilobate.

micropuncta - Perforation of calcitic shell, too fine to contain caecum but possibly extension of secreting plasmalemma.Fig.265.

middle lateral muscles - Pair of muscles in some lingulides originating on ventral valve between central muscles and diverging slightly posteriorly before insertion on dorsal valve.Fig.377.

mixoperipheral growth - Differs from holoperipheral growth in that posterior sector of valve increases in size anteriorly and toward other valve.Fig.284.

monticules - See tubercle.

monticulus - Narrow median fold of the pseudodeltidium of orthotetidines and triplesiidines.

mosaic - Pattern on interior of valve formed by outlines of adjacent fibers of secondary shell layer.Fig.242.

mouth segment - Median part of lophophore containing mouth; attached to anterior body wall and bearing single row of paired or unpaired tentacles.

mucronate - Cardinal extremities extended into sharp points.

muehlfeldtiform - See mediovertical.

multicostellate - Costellae increasing in number by bifurcation or intercalation but not varying greatly in size.Fig.297.

muscle area - See muscle field.

muscle field - Area of valve in which muscle scars are concentrated.

muscle impression - Marks of muscle attachment.

muscle platform - Solid or undercut elevation of shell to which muscles are attached.Fig.375.

muscle scar - More or less well-defined impression or elevation on valve representing final site of attachment of muscle.Fig.350.

muscle track - Path of successive muscle impressions formed by migration of muscle base during growth.Fig.350.

muscle-bounding ridge - Elevation composed of secondary shell bounding part of muscle field.

myocoelidium - Chamber similar to spondylium but not formed by dental plates serving for attachment of muscles as in richthofeniids.

myophore - Differentiated site of diductor muscle attachment on cardinal process consisting of ridged myotest.Fig.357,Fig.360.

myophragm - Ridge or septum of secondary shell dividing paired muscle scars that may encroach on its sides.

myotest - Muscle scar shell usually bearing impressions of the secretory cuboidal epithelium associated with the attached bases of muscle systems; commonly granular in texture and pitted by resorption in carbonate shells.Fig.350.

mystrochial plates - Pair of small plates buttressing spondylium posterolaterally, as in Amphigenia and some meristids.