macroelements Essential elements needed for plant
growth in relatively large amounts; C, H, O, P, K, N, S, Ca, Fe,
Mg.
macroevolution Evolutionary change on a grand scale, encompassing
the origin of novel designs, evolutionary trends, adaptive radiation,
and mass extinction.
macrofauna benthic animals larger than about 0.5
mm
macrofibril An aggregation of microfibrils in the
cell wall, visible with the light microscope.
macrogamete The larger of the two gamete types in a heterogametic
organism, considered the female gamete.
macromere
The largest size class of blastomeres in a cleaving embryo when
the blastomeres differ in size from one another.
macromolecule A very large molecule, generally used in reference
to carbohydrates, lipids, proteins, and nucleic acids.
macronucleus The larger of the two kinds of nuclei in ciliate protozoa;
controls all cell functions except reproduction.
macronutrient An essential nutrient for which an
animal has a large minimal daily requirement (greater than 100
mg) (e.g., calcium, phosphorus, magnesium, potassium, sodium,
and chloride along with carbohydrates, lipids, and proteins).
macroparasite Large parasite that does not multiply
in the host of interest. Examples are cestodes, trematodes, and
most nematodes in their definitive hosts.
macrophage A phagocytic cell type in vertebrates that performs crucial
functions in the immune response and inflammation, such as presenting
antigenic epitopes to T cells and producing several cytokines.
macrophage migration inhibitory factor (MIF) Cytokine
released by sensitized lymphocytes that tends to inhibit migration
of macrophages in the immediate vicinity, thus contributing to
accumulation of larger numbers of macrophages close to the site
of MIF release.
macrophytes See seaweeds.
macroplankton The component of the plankton that
consists of large organisms 2 to 20 cm in size.
macropores Large pore spaces caused by invertebrates
and larger animals, including reptiles and mammals, that permeate
the soil. They drain water not held by capillarity.
madreporite Sievelike structure
that is the intake for the water-vascular system of echinoderms.
magma Molten rock from deep in the earth's interior;
called lava when it spews from volcanic vents.
magnetic anomalies Magnetic bands in the sea floor
that run parallel to the mid-ocean ridge .
magnetic confinement A technique for enclosing
a nuclear fusion reaction in a powerful magnetic field inside
a vacuum chamber.
magnetite A magnetic, iron-containing material.
main thermocline See thermocline.
major histocompatibility complex (MHC). Complex
of genes coding for proteins inserted in the cell membrane; the
proteins are the basis of self-nonself recognition by the
immune system.
major mineral Mineral requirement needed in relatively
large amounts.
Malacostraca The class of crustaceans whose members
are characterized by having appendages modified for crawling along
the substrate, as in lobsters, crayfish, and crabs. Alternatively,
the abdomen and body appendages may be used in swimming, as in
shrimp.
malacostracan
Any member of the crustacean subclass Malacostraca, which includes
both aquatic and terrestrial forms of crabs, lobsters, shrimps,
pillbugs, sand fleas, and others.
malar mala = the jaw, cheek.
malate Four-carbon organic acid found with
aspartate to be the first products of the C4 pathway of photosynthesis.
male dominance polygyny A mating system in which
males compete and acquire dominance ranks that influence their
access to females, with higher-ranking males often having
greater mating activity.
male parasitism The permanent attachment of a male
to a female in some deep-sea fishes.
malignant tumor A mass of cancerous cells that
have left their site of origin, migrated through the body, invaded
normal tissues, and are growing out of control.
malleus The ossicle attached to the
tympanum in middle ears of mammals.
malnourishment A nutritional imbalance caused by
lack of specific dietary components or inability to absorb or
utilize essential nutrients.
malpighian tubules (Marcello Malpighi, Italian
anatomist, 1628-1694). Blind tubules opening into the hindgut
of nearly all insects and some myriapods and arachnids, and functioning
primarily as excretory organs.
Malthusian growth A population explosion followed
by a population crash; also called irruptive growth.
mamelon Ventral, serrated projection on the ventral
surface of a male nematode of the family Syphaciidae. Its function
is unknown.
Mammalia The class of vertebrates whose members are at least partially covered by hair, have specialized teeth, and are endothermic. Young are nursed from mammary glands. The mammals.
Mammalian Pertaining to animals
feeding their young with milk from a breast.
mammals Vertebrates that have
hair and mammary glands.
mammary gland The breast. In female mammals, the
mammary glands produce and secrete milk to nourish developing
young.
Man and Biosphere (MAB) program A design for nature
preserves that divides protected areas into zones with different
purposes. Critical ecosystem functions and endangered wildlife
are protected in a central core region where limited scientific
study is the only human access allowed. Ecotourism and research
facilities are located in a relatively pristine buffer zone around
the core, while sustainable resource harvesting and permanent
habitation are allowed in multiple-use peripheral regions.
mandibles Third pair of appendages from the anterior
in Crustacea; second pair in Insecta; primarily function in feeding;
derived from appendages on primitive fourth (first postoral) somite.
mangal a tropical community of mangrove plants
and associated organisms
manganese nodules Lumps of minerals (including
manganese and other valuable minerals) that are found on the sea
floor beyond the continental shelf.
mange Dermatitis caused by species of mites, often
designated with the causative organism. For example, Sarcoptes
causes sarcoptic mange.
mangroves Shrubs and trees that live along the
seashore in tropical and subtropical regions and tolerate inundation
by seawater.
mantle cavity The space between the mantle and
the visceral mass of molluscs.
mantle (1) The semi-liquid region between
the crust and core of the earth. (2) The outer layer of tissue
that secretes the shell of molluscs.
manubrium The portion projecting from
the oral side of a jellyfish medusa, bearing the mouth; oral cone;
presternum or anterior part of sternum; handle-like part
of malleus of ear.
marasmus Malnutrition,
especially of infants, caused by a diet deficient in both calories
and protein.
margin The edge of a flattened structure; in leaves,
the lateral edge of the blade.
marginal bodies Sensory pits or short tentacles
between the marginal loculi of the opisthaptor of an aspidogastrean
trematode.
marginal meristem The meristem along the margin
of a leaf primordium responsible with the formation and shape
of the leaf.
marginal value theorem A model that predicts when
an organism should cease foraging in one patch and travel to another.
mariculture The culture of marine organisms. In
open mariculture
(or semi-culture), organisms are cultured in natural environments;
in closed mariculture (or intensive mariculture), organisms are
cultured in a controlled environment.
marine Living in or pertaining to the sea.
marine archaeology The discovery, salvage, and
interpretation of material remains of humankind's past that have
been preserved in the sea.
marine natural products Chemical compounds that
are obtained from marine organisms.
marine snow Detritus and other particulate organic
matter that is found in the water column.
maritime culture A human culture with a very close
relationship with the sea.
market equilibrium The dynamic balance between
supply and demand under a given set of conditions in a "free"
market (one with no monopolies or government interventions).
marrara Nasopharyngeal blockage by a parasite.
Also called halzoun.
marsh Wetland without trees; in North America,
this type of land is characterized by cattails and rushes.
marsupial One of
the pouched mammals of the subclass Metatheria.
mass The fundamental unit of measurement equivalent
to the weight of a substance when compared with the weight of
hydrogen.
mass burn Incineration of unsorted solid waste.
masseter A chewer.
mass number Sum of the number of protons and neutrons
in the nucleus of an atom; designated by a superscript to the
upper left of the elemental symbol.
mast cell Type of cell in various tissues that
releases pharmacologically active substances with a role in inflammation.
mastax The pharyngeal apparatus of rotifers used
for grinding ingested food.
mastication Chewing.
mastigont Axoneme of a cilium or flagellum together
with its basal fibrils and organelles.
mastigophora The protozoan subphylum where members
possess one or more flagella that are used for locomotion; autotrophic,
heterotrophic, or saprozoic.
mastitis Infection of the udder of cattle.
mastoid A bony
process of the skull.
maternal Pertaining to the mother.
maternal condition model In polygynous mammals,
females that are high ranking, well nourished, or otherwise in
good condition giving birth to a greater proportion of sons since
their sons will outreproduce their daughters and vice versa for
females that are in poor condition.
mating system The species-typical pattern
of mate finding, reproduction, and parenting of offspring.
matric potential The water potential component caused by the attraction of water molecules to a hydrophilic matrix.
matrix The intercellular substance
of a tissue, or that part of a tissue into which an organ or process
is set; site of the Krebs cycle.
matter Anything that has mass and occupies space.
maturation To complete the natural development of
an animal system. Improvement in the performance of behavior occurs
as parts of the nervous system and other structures complete development.
Maurer's clefts Blotches on the surface of an erythrocyte
infected with Plasmodium falciparum.
maxilla One
member of a pair of mouthparts located just posterior to the mandibles
of many arthropods.
maxillae (second maxillae)Fifth pair of appendages
in Crustacea, primarily feeding in function, derived from appendages
on primitive sixth (third postoral) somite; homologous to labium
in insects. The maxillae of insects are the third pair of head
appendages, homologous to maxillules of Crustacea.
maxillary gland In malacostracan crustaceans, the
excretory organs are located near the maxillary segments and are
termed maxillary glands.
maxilliped One
of the pairs of head appendages located just posterior to the
maxilla in crustaceans, a thoracic appendage that has become incorporated
into the feeding mouthparts.
maxillopodan eye Naupliar eye of crustacean class
Maxillopoda; has a tapetum (crystalline reflective layer).
maxillules (first maxillae)Fourth pair of appendages
in Crustacea, primarily feeding in function; derived from appendages
on primitive fifth (second postoral) somite; homologous to maxillae
in insects.
maximum sustainable yield The maximum level of fishing
effort that a fish stock can withstand without causing major upsets
in the abundance of its stock.
meadow An open clearing in a landscape in which
low-growing, herbaceous plants dominate.
mean The central tendency of a series of measurements
or observations, calculated by summing all values in a distribution
and dividing the total by the number of values.
meatus A passageway.
mechanical vector Vector that transmits disease organism by mechanical means only. Contrast with biological vector.
mechanoreceptor A sensory receptor that is sensitive
to mechanical stimulation, such as changes in pressure or tension.
meconium A dark green mucilaginous material in the
intestine of the full-term fetus, being a mixture of the
secretions of the intestinal glands and some amniotic fluid.
medial On or near the plane that divides a bilateral
animal into mirror images. Also median.
median (parietal) eye A photoreceptor located middorsally
on the head of some vertebrates; it is associated with the vertebrate
epithalamus.
mediastinum
The membranes enclosing the tissues and organs between the two
lungs.
mediated transport. Transport of a substance across
a cell membrane mediated by a carrier molecule in the membrane.
Mediterranean climate areas Specialized landscapes
with warm, dry summers; cool, wet winters; many unique plant and
animal adaptations; and many levels of endemism.
medulla oblongata Portion of the brain stem located
between the pons and the spinal cord.
medulla The inner portion of an organ
in contrast to the cortex or outer portion. Also, hindbrain.
medusa A jellyfish, or the free-swimming stage in the life
cycle of cnidarians.
megacity See megalopolis.
megacolon Flabby distended colon caused by chronic
Chagas' disease.
megaesophagus Distended esophagus caused by chronic
Chagas' disease.
megagametogenesis The production of megagametes
(large gametes) from megaspores in the ovules of angiosperms.
megagametophyte The gametophyte stage containing
eight haploid nuclei within the embryo sac.
megalopolis Also known as a megacity or supercity;
megalopolis indicates an urban area with more than 10 million
inhabitants.
megaplankton The component of the plankton that
consists of very large organisms over 20 cm in size.
megasporangium Sporangium that contains megaspores.
megaspore Haploid cell produced by meiosis in the
ovules of angiosperms; a single megasporocyte produces four megaspores,
only one of which remains functional.
megaspore mother cell Diploid cell in megasporangium
that, upon undergoing meiosis, yields megaspores.
megasporocyte Also known as the megaspore mother
cell; this diploid cell undergoes meiosis to produce four haploid
megaspores in the ovules of angiosperms.
megasporogenesis The process of megaspores (large
spores) being produced via meiosis in the ovules of angiosperms.
megawatt (MW) Unit of electrical power equal to
one thousand kilowatts or one million watts.
Mehlis' glands Unicellular mucous and serous glands
surrounding the ootype of a flatworm.
meiofauna Small invertebrates found in the interstices between
sand grains.
meiosis Process of cell division by which egg and
sperm cells are formed, involving a diminution in the amount of
genetic material. Comprises two successive nuclear divisions with
only one round of DNA replication, which produces four haploid
daughter cells from an initial diploid cell.
meiotic Cell division that reduces
the number of chromosomes from diploid to haploid.
Meissner'scorpuscles Tactile sensory receptors
in the superficial dermis.
melanin Black or dark-brown
pigment found in plant or animal structures.
melanism Dark coloration of the skin, fur, or feathers
because of the presence of the pigment melanin.
melanophore Black or brown chromatophore containing melanin.
melatonin A hormone secreted by the pineal gland.
Functions in regulating photoperiodicity.
melon A fatty structure on the forehead of some
cetaceans that is used to direct sound waves emitted during echolocation.
membrane In living organisms, a phospholipid bilayer
impregnated with protein and certain other compounds; functions
in partitioning of cellulose activities.
membrane selectivity See differentially permeable
membrane.
membranelle Short, transverse rows of cilia, fused
at their bases, serving to move food particles toward the oral
groove of a protozoan.
memory The capacity of an organism to form lasting
connections based on past experiences; the ability to store and
use information.
memory cell A lymphocyte capable of initiating
the antibody- mediated immune response on detection of a
specific antigen molecule for which it is genetically programmed.
It circulates freely in the blood and lymph, and may live for
years.
memory trace See engram.
meninges Any
of three membranes (arachnoid, dura mater, pia mater) that envelop
the vertebrate brain and spinal cord. Also, solid connective tissue
sheath enclosing the central nervous system of some vertebrates.
menisci A crescent-shaped
fibrocartilage.
menopause
In the human female, that time of life when ovulation ceases;
cessation of the menstrual cycle.
menses The period of shedding of the lining (endometrium)
of the uterus and associated fluids if an ovum is not fertilized,
most notably in primates.
menstrual cycle The period of the regularly recurring
physiologic changes in the endometrium that culminates in its
shedding (menstruation).
menstruation Loss of blood and tissue from the uterus
at the end of a female primate's reproductive cycle.
meristem The tissue or
zone from which new cells are produced by cell division.
meristematic tissue Within some seaweeds, specific
tissue sites where most cell division for growth occurs.
meroblastic
Partial cleavage occurring in zygotes having a large amount of
yolk at the vegetal pole; cleavage restricted to a small area
on the surface of the egg.
merogony Multiple fission to produce merozoites; schizogony.
meroplankton Planktonic organisms that spend only
part of their life in the plankton. Compare holoplankton.
Merostomata The class of arthropods whose members
are aquatic and possess book gills on the opisthosoma. Eurypterids
(extinct) and horseshoe crabs.
merozoite A
very small trophozoite at the stage just after cytokinesis has
been completed in multiple fission of a protozoan.
mesenchyme Undifferentiated mesoderm. It will eventually
develop into muscle, blood vessels, skeletal elements, and (other)
connective tissues.
mesenterial filament Any of the long, thin tubes
attached to the gut of corals and other cnidarians that are involved
in digestion and absorption.
mesenteries Infoldings of gastroderm and mesoglea
extending into the gastrovascular cavity of cnidarians; sheets
of peritoneum from which the digestive tract is suspended in coelomates.
mesentery Peritoneal
fold serving to hold the viscera in position.
mesic Referring to a region that receives adequate
precipitation to maintain biological productivity.
mesocarp The middle layer of the fruit wall, located
between the exocarp and endocarp.
mesocercaria Juvenile stage of the digenetic trematode
Alaria. It is an unencysted form between the cercaria and the
metacercaria.
mesocoel
Middle body coelomic compartment in some deuterostomes, anterior
in lophophorates, corresponds to hydrocoel in echinoderms.
mesoderm The
third germ layer, formed in the gastrula between the ectoderm
and endoderm; gives rise to connective tissues, muscle, urogenital
and vascular systems, and the peritoneum.
mesoglea The
layer of jellylike or cement material between the epidermis and
gastrodermis in cnidarians and ctenophores; also may refer to
jellylike matrix between epithelial layers in sponges.
mesohyl Gelatinous
matrix surrounding sponge cells; mesoglea, mesenchyme.
mesolecithal
Pertaining to a zygote (or ovum) having a moderate amount of yolk
concentrated in the vegetal pole.
mesonephros
The middle of three pairs of embryonic renal organs in vertebrates.
Functional kidney of fishes and amphibians; its collecting duct
is a Wolffian duct. Adj., mesonephric.
mesopelagic zone The pelagic environment from a
depth of approximately 100 to 200 m (350 to 650 ft) to 1,000 m
(3,000 ft).
mesophyll Photosynthetic middle layer in the blade
of a leaf; typically composed of palisade and spongy parenchyma.
mesophyte A plant that grows in soils that contain
moderate or intermediate amounts of moisture.
mesoplankton The component of the plankton that
consists of organisms 0.2 to 2 mm in size .
mesosome The
portion of the body in lophophorates and some deuterostomes that
contains the mesocoel.
mesosphere The atmospheric layer above the stratosphere
and below the thermosphere; the middle layer; temperatures are
usually very low.
mesothorax The middle of the three thoracic segments
of an insect; usually contains the second pair of legs and the
first pair of wings.
Mesozoa A phylum of animals whose members are parasites
of marine invertebrates. With a two-layered body organization.
Dioecious, complex life histories. Orthonectids and dicyemids.
Mesozoic The geological era beginning about 250
million years ago. During this time gymnosperm forests, dinosaurs,
mammals, birds, and flowering plants appeared. By the end of the
Mesozoic, about 70 million years ago, dinosaurs became extinct.
messenger RNA A single-stranded polyribonucleotide;
formed in the nucleus from a DNA template and carries the transcribed
genetic code to the ribosome where the genetic code is translated
into protein.
metabolic energy That energy obtained from ATP
produced in metabolism.
metabolism A group of processes
that includes digestion, production of energy (respiration), and
synthesis of molecules and structures by organisms; the sum of
the constructive (anabolic) and destructive (catabolic) processes.
metabolites Chemical substances required in metabolism.
metacentric Chromosome with centromere at or near the middle.
metacercaria Stage between the cercaria and adult
in the life cycle of most digenetic trematodes; usually encysted
and quiescent.
metacestode Developmental stage of a cestode after
metamorphosis of the oncosphere; a juvenile cestode.
metacoel Posterior coelomic compartment in some deuterostomes
and lophophorates; corresponds to somatocoel in echinoderms.
metacommunication Communication about communication,
where one signal changes the meaning of signals that follow.
metacryptozoite Merozoite developed from a cryptozoite.
metacyclic Stage in the life cycle of a parasite
that is infective to its definitive host.
metacyst Cystic stage of a parasite that is infective
to a host.
metamere A repeated
body unit along the longitudinal axis of an animal; a somite,
or segment.
metamerism Division of the body along the anteroposterior
axis into a serial succession of segments, each of which contains
identical or similar representatives of all the organ systems
of the body; primitively in arthropods, including externally a
pair of appendages and internally a pair of nerve ganglia, a pair
of nephridia, a pair of gonads, paired blood vessels and nerves,
and a portion of the digestive and muscular systems.
metamorphic rock A type of rock, either granitic
or sedimentary in origin, and structurally changed by high temperature
and pressure.
metamorphosis Type of development in which one
or more juvenile types differ markedly in body form from the adult;
occurs in numerous animal phyla. Also applies to the actual process
of changing from larval to adult form.
metanauplius Later naupliar larvae of some crustaceans;
that is, occurring after several naupliar stages but before another
larval type or preadult in the developmental sequence.
metanephridium An excretory organ found in many
invertebrates; it consists of a tubule that has one end opening
at the body wall and the opposite end in the form of a funnel-like
structure that opens to the body cavity.
metanephros Embryonic renal organs of vertebrates arising
behind the mesonephros; the functional kidney of reptiles, birds,
and mammals. It is drained from a ureter.
metaphase Stage in mitosis when chromosomes become
aligned in the middle of the cell and firmly attached to the mitotic
spindle but have not yet segregated toward opposite poles.
metapodosoma Portion of the podosoma that bears
the third and fourth pairs of legs of a tick or mite.
metapolar cells Posterior tier of cells in the
calotte of a dicyemid mesozoan.
metasome
The portion of the body in lophophorates and some deuterostomes
that contains the metacoel.
metathorax The posterior of the three segments of
an insect thorax; it usually contains the third pair of walking
legs and the second pair of wings (Arthropoda).
metazoa Multicellular
animals.
metazoan A multicellular animal.
methane CH4, natural gas.
methanogen A bacterium that obtains energy from
CO2 and H2 and forms methane.
metraterm Muscular, distended termination of the
uterus of a digenetic trematode.
MHC See major histocompatibility complex.
micelle Lipid aggregates with a surface coat of
bile salts. A stage in the digestion of lipids in the small intestine.
micro-hydro generators Small power generators
that can be used in low-level rivers to provide economical
power for four to six homes, freeing them from dependence on large
utilities and foreign energy supplies.
microatoll A small, flat, atoll-shaped coral
structure generally found in protected coral lagoons.
microbial loop A component of epipelagic food webs
in which dissolved organic matter is cycled through the picoplankton
and nanoplankton back into the main part of the food web.
microbody Membrane-bound organelles that are
the site of certain enzymatic conversions; example: peroxisomes
and glyoxisomes.
microevolution A change in the gene pool of a population across generations.
microfauna benthic animals smaller than about 0.1 mm
microfibril An elongated strand of cellulose molecules.
microfilament Component of the cytoskeleton; involved
in cell shape, motion, and growth. Helical protein filament formed
by the polymerization of globular actin molecules.
microfilaria The prelarval stage of filarial worms.
Found in the blood of humans and the tissues of the vector.
microfilariae Partially developed juveniles borne alive by filarial
worms (phylum Nematoda).
microfossils The microscopic shells and other remains
of marine organisms that make up biogenous sediments.
microgamete
The smaller of the two gamete types in a heterogametic organism,
considered the male gamete.
microgametocyte Cell that gives rise to microgametes.
microgametogenesis The production of microgametes
(small gametes) from microspores in the anthers of flowering plants.
micromere The
smallest size class of blastomeres in a cleaving embryo when the
blastomeres differ in size from one another.
micron (m) One one-thousandth
of a millimeter; about 1/25,000 of an inch. Now largely replaced
by micrometer (mm).
microneme
One of the types of structures composing the apical complex in
the phylum Apicomplexa, slender and elongate, leading to the anterior
and thought to function in host cell penetration.
micronemes Slender, convoluted bodies that join
a duct system with the rhoptries, opening at the tip of a sporozoite
or merozoite.
microniscus Intermediate larval stages of the isopod
suborder Epicaridea, parasitic on free-living copepods.
micronucleus A small body of DNA that contains the
hereditary information of ciliates (Protista); exchanged between
protists during conjugation. It undergoes meiosis before functioning
in sexual reproduction.
micronutrient A dietary element essential in only
small quantities (e.g., iron, chlorine, copper, and vitamins).
microorganisms Single-celled living organisms
that can be seen only with the aid of a microscope.
microparasite Small (or very small) parasite that
multiplies within the host of interest. Examples are protistan
and prokaryotic parasites.
microplankton The component of the plankton that
consists of organisms 20 to 200 mm (0.02 to 0.2 mm) in size.
micropores Spaces between soil particles that hold
water by means of capillary forces.
micropredator Temporary parasite.
micropyle
The small opening through which the cells emerge from a gemmule
(phylum Porifera).
microscopy Examination with a microscope.
microspora The protozoan phylum characterized by
members having unicellular spores; intracellular parasites in
nearly all major animal groups. Examples: microsporeans (Nosema).
microsporangium The structure
(sporangium) in which microspores are produced.
microspore Haploid cells produced by meiosis in
the anthers of angiosperms; four microspores are produced from
a single microsporocyte.
microspore mother cell Diploid cell in microsporangium
that undergoes meiosis to produce microspores.
microsporocyte Also known as the microspore mother
cell, this diploid cell undergoes meiosis to produce four haploid
microspores in the anthers of angiosperms.
microsporogenesis The process of microspores (small
spores) being produced via meiosis in the anthers of angiosperms.
microsporophyll A leaflike structure giving rise
to one or more microsporangia.
microthrix (microtriches) Minute projections of
the tegument of a cestode.
microtubule A hollow cylinder of tubulin subunits;
involved in cell shape, motion, and growth; functional unit of
cilia and flagella. It is one of three major classes of filaments
of the cytoskeleton.
microvillus Narrow, cylindrical cytoplasmic projection from epithelial
cells; microvilli form the brush border of several types of epithelial
cells. Also, microvilli with unusual structure cover the surface
of cestode tegument (also called microthrix [pl. microtriches]).
mictic Pertaining
to haploid egg of rotifers or the females that lay such eggs.
mictic eggs Pertaining to the haploid eggs of rotifers.
If it isn't fertilized, the egg develops parthenogenetically into
a male; if fertilized, mictic eggs secrete a heavy shell and become
dormant, hatching in the spring into amictic females.
midbrain The portion of the brain between the pons
and forebrain.
mid-ocean ridge The continuous chain of volcanic
submarine mountains that extends around the earth. It includes
the Mid-Atlantic Ridge and East Pacific Rise.
middle lamella Layer of adhesive material (primarily
pectins) found between adjacent cell walls.
midrib The central large vein of a leaf.
midwater Pertaining to the mesopelagic zone.
Miescher's tubules Sarcocysts; tissue cysts of
Sarcocystis.
migration A seasonal movement from one location
to another.
Milankovitch cycles Periodic variations in tilt,
eccentricity, and wobble in the earth's orbit; Milutin Milankovitch
suggested that it is responsible for cyclic weather changes.
milpa agriculture An ancient farming system in
which small patches of tropical forests are cleared and perennial
polyculture agriculture practiced and is then followed by many
years of fallow to restore the soil; also called swidden agriculture.
mimicry When one species resembles one or more other
species; often protection is afforded the mimic species.
mineral A naturally occurring, inorganic, crystalline
solid with definite chemical composition and characteristic physical
properties.
mineralocorticoids Hormones
of the adrenal cortex, especially aldosterone, that regulate salt
balance.
miracidium The ciliated, free-swimming first
stage larva of a digenean trematode that undergoes further development
in the body of a snail.
Mississippian Part of the Carboniferous period,
beginning around 360 million years ago.
mitigation Repairing or rehabilitating a damaged
ecosystem or compensating for damage by providing a substitute
or replacement area.
mitochondria in eucaryotes, a subcellular organelle
that conducts cellular respiration
mitochondrion Membrane-bounded organelle that
specializes in aerobic respiration (oxidative phosphorylation)
and produces most of the ATP in eukaryotic cells.
mitosis
Nuclear division in which there is an equal qualitative and quantitative
division of the chromosomal material between the two resulting
nuclei; ordinary cell division.
mitotic apparatus Collectively, the asters, spindle,
centrioles, and microtubules of a dividing cell.
mixed perennial polyculture Growing a mixture of
different perennial crop species (where the same plant persists
for more than one year) together in the same plot; imitates the
diversity of a natural system and is often more stable and more
suitable for sustainable agriculture than monoculture of annual
plants.
mixed semidiurnal tide A tidal pattern with two
successive high tides of different heights each day.
modal action pattern (MAP) A spatiotemporal behavior
pattern that is common to members of a species; different individuals
perform the pattern in a recognizably similar fashion.
modern synthesis The combination of principles of
population genetics and Darwinian evolutionary theory.
modification A change, as in morphology, usually
associated with a functional advantage.
molar L. molaris = a grinder.
mole One gram molecular weight of any substance;
that is, the molecular weight of any substance in grams.
molecule A particle composed of two or more atoms bonded together. An aggregate of at least two atoms in a definite arrangement held together by special forces.
molecular biology The study of the biochemical structure
and function of organisms.
molecular genetics The study of the biochemical
structure and function of DNA.
molecular weight The sum of all the atomic weights of a molecule.
Mollusca The phylum of coelomate animals whose members
possess a head-foot, visceral mass, mantle, and mantle cavity.
Most molluscs also possess a radula and a shell. The molluscs.
Bivalves, snails, octopuses, and related animals.
molluscs Invertebrates with a
soft, unsegmented body, a muscular foot, and, with some exceptions,
a calcareous shell.
molt A process in arthropods, such as crustaceans
and insects, as well as in some vertebrates, such as snakes, whereby
the organism sheds its outer exoskeleton or skin periodically
as it grows. Also refers to changing the pelage or feathers in
a mammal or bird.
molt The exoskeleton that is shed during the molting
process.
molting See ecdysis.
Monera The kingdom of life whose members are characterized
by having cells that lack a membrane-bound nucleus, as well
as other internal, membrane-bound organelles (they are prokaryotic);
bacteria.
monerans Members of the kingdom Monera, which consists
of prokaryotic organisms.
monestrous A species in which the female is receptive
for only a few days once each year.
monitored, retrievable storage Holding wastes in
underground mines or secure surface facilities such as dry casks
where they can be watched and repackaged, if necessary.
monkey wrenching Environmental sabotage such as
driving large spikes in trees to protect them from loggers, vandalizing
construction equipment, pulling up survey stakes for unwanted
developments, and destroying billboards.
monocarpic Denoting a plant that flowers only once.
monocot One of the two primary groups of angiosperms
characterized by a single cotyledon, parallel venation of leaves,
and floral parts in threes.
monocotyledon A class of angiosperms in which the
seedlings typically possess one cotyledon. Commonly abbreviated
to monocot.
monoculture An agricultural system in which only
one crop species is cultivated.
monoculture agroforestry Intensive planting of
a single species; an efficient wood production approach, but one
that encourages pests and disease infestations and conflicts with
wildlife habitat or recreation uses.
monocyte
A type of leukocyte that becomes a phagocytic cell (macrophage)
after moving into tissues.
monoecious Hermaphroditic; an individual that contains
reproductive systems of both sexes.
monogamous Having one mate at a time.
monogamy The condition of having a single mate at any
one time.
Monogenea The class of Platyhelminthes that has
members that are called monogenetic flukes; most ectoparasites
on vertebrates (usually on fishes, occasionally on turtles, frogs,
copepods, squids); one life-cycle form in only one host;
bear an opisthaptor. Examples: Disocotyle, Gyrodactylus, Polystoma.
Monogononta A class of rotifers containing members
that possess one ovary; mastax not designed for grinding; produce
mictic and amictic eggs. Example: Notommata.
monohybrid cross A mating between two individuals
heterozygous for one particular trait.
monohybrid
A hybrid offspring of parents different in one specified character.
monomer A molecule
of simple structure, but capable of linking with others to form
polymers.
monophyletic groups Groups that contain an ancestor
and all the descendants of that ancestor.
monophyletic origin A group of organisms that evolved
from a single ancestral type.
monophyly
The condition that a taxon or other group of organisms contains
the most recent common ancestor of the group and all of its descendants;
contrasts with polyphyly and paraphyly.
Monoplacophora The class of molluscs whose members
have a single, arched shell; a broad, flat foot; and certain serially
repeated structures. Neopilina.
monoplacophorans A small
group of molluscs that are thought by some to represent a link
with invertebrates that show segmentation.
monosaccharide A simple sugar that cannot
be decomposed into smaller sugar molecules; the most common are
pentoses (such as ribose) and hexoses (such as glucose).
monostome Fluke that lacks a ventral sucker.
monounsaturated fat Composed of fatty acid chains
in which there is only a single C-C double bond; examples:
canola oil and olive oil.
monoxenous Living within a single host during
a parasite's life cycle.
monozoic Tapeworms
with a single proglottid, do not undergo strobilation to form
chain of proglottids.
monozygotic Twins that arise from a single zygote,
hence, two genetically identical individuals.
monsoon A seasonal reversal of wind patterns caused
by the different heating and cooling rates of the oceans and continents.
montane coniferous forests Coniferous forests of
the mountains consisting of belts of different forest communities
along an altitudinal gradient.
moral agents Beings capable of making distinctions
between right and wrong and acting accordingly. Those whom we
hold responsible for their actions.
moral subjects Beings that are not capable of distinguishing
between right or wrong or that are not able to act on moral principles
and yet are susceptible of being wronged by others. This category
assumes some rights or inherent values in moral subjects that
gives us duties or obligations towards them.
morbidity Illness or disease.
more-developed countries (MDC) Industrialized
nations characterized by high per capita incomes, low birth and
death rates, low population growth rates, and high levels of industrialization
and urbanization.
morphine A pain-relieving and addictive compound
derived from the opium poppy (Papaver somniferum).
morphogenesis
Development of the architectural features of organisms; formation
and differentiation of tissues and organs.
morphology The science of structure. Includes cytology,
the study of cell structure; histology, the study of tissue structure;
and anatomy, the study of gross structure.
mortality Death rate in a population; the probability
of dying.
morula A stage in the embryonic development of some animals that consists of a solid ball of cells.
mosaic An organism whose tissues are made up of
two or more genetically different types.
mosaic cleavage. Embryonic development characterized
by independent differentiation of each part of the embryo; determinate
cleavage.
mosaic evolution A change in a portion of an organism
(e.g., a bird wing) while the basic form of the organism is retained.
moss A group of terrestrial, nonvascular plants;
the dominant plant body is the gametophyte with the sporophyte
embedded in it.
motility Ability to move.
motivation Internal processes that arouse and direct
behavior. Today this refers more to examination of the consequences
of behavior and feedback to the animal concerning the consequences
of those actions.
motor (efferent) neuron or nerve A neuron or nerve that transmits impulses from the central nervous system to an effector such as a muscle or gland.
motor neuron A neuron that synapses with a muscle
membrane.
motor unit A motor neuron and the muscle fibers
associated with it.
mountain tundra That portion of tundra vegetation
confined to alpine meadows. Low-growing grasses, sedges,
and forbs with a very short growing season; permafrost is typical.
mucigel A slimy material secreted by and covering
the root cap and root hairs.
mucilaginous Containing a mucilage, usually composed
of mucopolysaccharides.
mucin Any of a group of
glycoproteins secreted by certain cells, especially those of salivary
glands.
mucous cell A glandular cell that secretes mucus.
mucron Apical anchoring device on an acephaline
gregarine protozoan.
mucus Viscid, slippery
secretion rich in mucins produced by secretory cells such as those
in mucous membranes. Adj., mucous.
mud flat A muddy bottom that is exposed at low
tide.
Muellerian mimicry Evolution by one species to
resemble the coloration, body shape, or behavior of an unrelated
species that is protected from predators by a venomous stinger,
bad taste, or some other adaptation.
mulch Protective ground cover, including manure,
wood chips, straw, seaweed, leaves, and other natural products,
or synthetic materials, such as heavy paper or plastic, that protect
the soil, save water, and prevent weed growth.
Mullerian mimicry Occurs when two similar
species are both distasteful to predators.
Mullerian mimics Noxious species that resemble
each other.
Muller's larva A free-swimming ciliated larva
that resembles a modified ctenophore, characteristic of many marine
polyclad turbellarians.
Muller's ratchet The steady accumulation of mutations
in a population of asexual organisms over time.
Müller's larva. Free-swimming ciliated
larva that resembles a modified ctenophore, characteristic of
certain marine polyclad turbellarians.
multigenic (polygenic) inheritance Inheritance
in which the genetic control for a trait results in the phenotypic
expression varying continuously.
multiple alleles A condition in which more than
two alleles exist for a given trait.
multiple fission Asexual reproduction by the splitting
of a cell or organism into many cells or organisms. See schizogony.
multiple fruit A fruit derived from the fusion
of the ovaries of several flowers in an inflorescence; example:
pineapple.
multiple use Many uses that occur simultaneously;
used in forest management; limited to mutually compatible uses.
muscle fiber The contractile unit of a muscle.
muscle tissue The type of tissue that allows movement.
The three kinds are skeletal, smooth, and cardiac. Tissue made
of bundles of long cells called muscle fibers.
muscleL. musculus = a contractile organ.
muscularis mucosae Smooth muscle fibers around
the mucosa of the gut wall, surrounding the lamina propria and
surrounded by the submucosa.
mushroom Common name for a group of fungi (Basidiomycetes) that produce an aboveground reproductive structure.
musk gland See scent gland.
mutagen Any substance capable of causing a mutation.
mutagens Agents, such as chemicals or radiation,
that damage or alter genetic material (DNA) in cells.
mutation pressure The constant resupplying of mutations
to a gene pool due to a base mutation rate.
mutation A change, either spontaneous or by external
factors, in the genetic material of a cell; mutations in the gametes
(sex cells) can be inherited by future generations of organisms.
mutational analysis An analysis that examines the
effects of specific mutants for the effects on particular phenomena
with respect to morphology, physiology, or behavior.
mutualism
A type of interaction in which two different species derive benefit
from their association and in which the association is necessary
to both; often symbiotic.
mycelium A network of fungal hyphae.
mycetome Specialized organ in some insects that
bears mutualistic bacteria.
mycobiont The fungal partner in a mutualistic relationship
such as mycorrhizae or lichens.
mycologist A person who studies
fungi.
mycorrhiza Symbiotic association
between a fungus and a plant root.
mycotoxin A toxic compound formed by the hyphae
of common molds growing under a variety of conditions, especially
in contaminated foods.
myelin A fatty material forming
the medullary sheath of nerve fibers.
myiasis Infection by fly maggots.
myocyte
Contractile cell (pinacocyte) in sponges.
myofibril A contractile filament within muscle or muscle fiber.
myogenic Originating in muscle, such as heartbeat arising in vertebrate cardiac muscle because of inherent rhythmical properties of muscle rather than because of neural stimuli.
myoglobin The oxygen-transporting pigment of
muscle tissue.
myomere The muscle plate or portion of a somite
that develops into voluntary muscle.
myosin A large protein of contractile tissue that forms the thick
myofilaments of striated muscle. During contraction it combines
with actin to form actomyosin.
myotome That
part of a somite destined to form muscles; the muscle group innervated
by a single spinal nerve.
myriapods Members of the four noninsect classes
of the subphylum Uniramia. Includes centipedes, millipedes, pauropods,
and symphylans.
Myxini The class of vertebrates whose members are
fishlike, jawless, without paired appendages, and possess four
pairs of tentacles around the mouth. Hagfishes.
Myxozoa The protozoan phylum characterized by members
having spores of multicellular origin; the myxozoans.
myzorhynchus Apical stalked, suckerlike organ on
the scolex of some tetraphyllidean cestodes.