UCMP Glossary: M
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macroscopic -- Objects or organisms that are large enough to be seen with the naked eye.
mafic -- Term used to describe the amount of dark-colored iron and magnesium minerals in an igneous rock. Complement of felsic.
magma -- n. Molten rock generated within the Earth; forms intrusive (solidifies below the surface) and extrusive (solidifies above the surface) igneous rocks.
magnoliid -- Any member of the basal assemblage of flowering plants.
male -- In organisms with separate sexes, the one which produces sperm.
mannoxylic -- Wood in which there is a great deal of parenchyma tissue among the xylem is called mannoxylic. Cycads and pteridosperms have mannoxylic wood. Contrast with pycnoxylic.
mantle -- That portion of the interior of the Earth that lies between the crust and the core.
marine terrace -- n. A platform of marine deposits (typically sand, silt, gravel) sloping gently seaward. Such a platform may be exposed along the coast, forming cliffs, due to uplift and/or the lowering of sea level, e.g., Marine terraces of coastal Southern California.
marl -- n. A loose, crumbly deposit consisting of clay and calcium carbonate and formed in marine or freshwater conditions.
marsupial -- n. (adj.) A mammal whose young are born while still embryos, and must crawl into its mother’s external pouch (called the marsupium) to finish development.
mastigoneme -- Small hair-like filaments found on the "hairy" flagellum of the Chromista.
megaspore -- In plants which are heterosporous, the larger kind of spore is called a megaspore; it usually germinates into a female (egg-producing) gametophyte. Contrast with microspore.
meiosis -- A two-stage type of cell division in sexually reproducing organisms. In meiosis, a diploid cell divides to produce four haploid cells, each with half the original chromosome content. For this reason, meiosis is often called a "reduction division". In organisms with a diploid life cycles, the products of meiosis are usually called gametes. In organisms with an alternation of generations, the products of meiosis are caled spores.
melange -- A body of rocks consisting of large blocks (mappable size) of different rocks jumbled together with little continuity of contacts.
membrane -- Semi-fluid structure which bounds all cells, and partitions the interior of eukaryotic cells. It consists primarily of two lipid layers, with proteins "dissolved" in the lipids.
meristem -- Group of undifferentiated cells from which new tissues are produced. Most plants have apical meristems which give rise to the primary tissues of plants, and some have secondary meristems which add wood or bark.
merophytes -- Group of cells which have all been produced from the same initial cell. Leaves and stems in particular are often built from specific patterns of merophytes.
mesoderm -- In animals with three tissue layers (i.e. all except sponges and cnidarians), the middle layer of tissue, between the ectoderm and the endoderm. In vertebrates, for instance, the mesoderm forms the skeleton, muscles, heart, spleen, and many other internal organs.
mesogloea -- Jellylike material between the outer ectoderm and the inner endoderm of cnidarians. May be very thin or may form a thick layer (as in many jellyfish).
mesokaryotic -- Nuclear condition unique to the dinoflagellates in which the chromosomes remain permanently condensed.
metamorphic rock -- Any rock derived from other rocks by chemical, mineralogical and structural changes resulting from pressure, temperature or shearing stress.
metamorphism -- n. The process of altering the chemical or mineralogical composition of a rock through different amounts of heat and pressure below the surface of the Earth; metamorphose- v; metamorphic - adj.
metamorphosis -- n. A process of developmental change whereby a larva reaches adulthood only after a drastic change in morphology; occurs in most amphibians and insects, for some insects, this change may include another stage (pupa) before the adult stage; metamorphose- v.
microfossil -- n. A very small fossil, best studied with the aid of a microscope, e.g. foraminifera, radiolarians, and small vertebrate fossils such as teeth. macrofossil– ant.
microphyll -- A kind of leaf, specifically one which has a single, unbranched vein in it. Microphylls are only found in the lycophytes.
microscopic -- Objects or organisms that are too small to be seen with the naked eye.
microspore -- In plants which are heterosporous, the smaller kind of spore is called a microspore; it usually germinates into a male (sperm-producing) gametophyte. Contrast with megaspore.
microtubules -- Type of filament in eukaryotic cells composed of units of the protein tubulin. Among other functions, it is the primary structural component of the eukaryotic flagellum.
microvilli -- Thin fingerlike protrusions from the surface of a cell, often used to increase absorptive capacity or to trap food particles. The "collar" of choanoflagellates is actually composed of closely spaced microvilli.
mid-oceanic ridges -- Elongated rises on the ocean floor where basalt periodically erupts, forming new oceanic crust; similar to continental rift zones.
mineralization -- The process of replacing any organism’s original material with a mineral.
mitochondrion -- Complex organelle found in most eukaryotes; believed to be descended from free-living bacteria that established a symbiotic relationship with a primitive eukaryote. Mitochondria are the site of most of the energy production in most eukaryotes; they require oxygen to function. See: double membrane.
mitosis -- The process of nuclear division in eukaryotes. It is one step in cytokinesis, or cellular division. MORE ?.
molds -- Fossils formed when the sediment surrounding a buried organism hardens. When the organism decays, its impression is left in the rock and can be seen if the rock is broken open.
monophyletic -- Term applied to a group of organisms which includes the most recent common ancestor of all of its members and all of the descendants of that most recent common ancestor. A monophyletic group is called a clade. More?
monsoonal -- adj. Describes a climate pattern with a wind system that changes direction with the seasons; this pattern is dominant over the Arabian Sea and Southeast Asia.
moraine -- n. A mound or ridge of sediment deposited by a glacier; lateral moraine- n. deposited to the side of a glacier; terminal moraine- n. deposited to the front of a glacier; ground moraine- n. deposited on the land surface.
morphology -- n. The form and structure of anything, usually applied to the shapes, parts, and arrangement of features in living and fossil organisms.
motile -- Able to move oneself about, capable of self-locomotion.
mouth -- Front opening of the digestive tract, into which food is taken for digestion. In flatworms, the mouth is the only opening into the digestive cavity, and is located on the "belly" of the worm.
MTOC -- (microtubule organizing center) MTOCs are bundles of protein tubes which may be found at the base of a eukaryotic flagellum. In animals, they also function in creating the arrays of microtubules that pull the chromosomes apart during mitosis.
mucus -- Sticky secretion used variously for locomotion, lubication, or protection from foreign particles.
multicellular -- Any organism which is composed of many cells is termed multicellular.
muscle -- Bundle of contractile cells which allow animals to move. Muscles must act against a skeleton to effect movement.
mycorrhizae -- Symbiotic association between a fungus and the roots or rhizoids of a plant. More info?
myotome -- Segment of the body formed by a region of muscle. The myotomes are an important feature for recognizing early chordates.
