Mutationism see De Vriesianism

mutation rate Frequency with which a mutation occurs per site per generation.

mutation theory A theory of the origin of new characteristics in organisms as a result of changes in the genes. see saltation.

mutator genes Any gene that causes an increase in mutation rates in other genes. see mutafacient.

mutein n. [L. mutatus, change; Eng. protein] A mutationally altered protein analogous to the normal type.

mutic, mutilous a. [L. muticus; shortened] Unarmed; lacking defensive processes that usually occur.

mutilate v.t. [L. mutilus, cut-off] To deprive of one or more essential part(s); to amputate.

muton n. [L. mutare, to change] The smallest element in the array of mutation sites, that when altered, may give rise to a mutant.

mutualism n. [L. mutuus, reciprocal] A type of symbiosis in which both host and symbiont benefit from the association.

myarian a. [Gr. mys, muscle] 1. Referring to muscle, as in meromyarian. 2. (MOLL: Bivalvia) Used in classification as to number and position of the adductor muscles.

mycelium n. [Gr. mykes, fungus] In fungi, the network of filaments that form the vegetative part.

mycetangium n. [Gr. mykes, fungus; angeion, vessel] (AR-THRO: Insecta) The fungus-storing organs of Platypodinae, a sac-like invagination of the epidermis at the posterior part of the prothorax.

mycetocyte n. [Gr. mykes, fungus; kytos, container] A large, polyploid cell containing intracellular mutualistic and com-mensalistic microsymbiotes; one of many cells that make up the mycetome. see symbiosis.

mycetome n. [Gr. mykes, fungus; -oma, mass] A specialized structure or organ that houses symbiotes.

mycetometochy n. [Gr. mykes, fungus; metochos, sharing] (ARTHRO: Insecta) Symbiosis between fungi and the dwellers of compound nests.

mycetophagous a. [Gr. mykes, fungus; phagein, to eat] Feeding on fungi; mycophagous; fungivorous.

mycohelminths [Gr. mykes, fungus; helmins, worm] Fungivorous nematodes.

mycophagous a. [Gr. mykes, fungus; phagein, to eat] Feeding on fungi; mycetophagous; fungivorous.

mycosis n. [Gr. mykes, fungus; -sis, process of] Any disease caused by the invasion of fungi.

mycotoxin n. [Gr. mykes, fungus; toxikon, poison] A low molecular weight metabolite of fungi which is poisonous to animals.

myelin sheath A fatty material surrounding a nerve fiber.

myiasis n. [Gr. myia, fly; -iasis, morbid condition] A condition deriving from invasion by dipterous larvae.

myoblast n. [Gr. mys, muscle; blastos, bud] A cell that produces muscular fiber.

myochordotonal organ (ARTHRO: Crustacea) In Decapoda, a proprioceptor at the proximal end of the meropodite, a flat membrane lying between the skeleton and sheath of the accessory flexor muscle of the carpus, with distal bipolar sensory cells passing through the membrane and attached to the skeleton; having scolopidia similar to the insect chordotonal organs.

myocytes [Gr. mys, muscle; kytos, container] (PORIF) Cells that cause contraction.

myoepithelial n. [Gr. mys, muscle; epi, upon; thele, nipple] 1. (BRYO) A contractile ectodermal cell with intracellular striated muscles. 2. (CNID) Epithelium with a longitudinal contractile fiber at the base; epitheliomuscular.

myofibrillae, myofibrils; sing. -a [Gr. mys, muscle; dim. fibra, fiber] Longitudinal fibrils of muscle cells.

myogenic a. [Gr. mys, muscle; gennaein, to produce] Pertains to a muscle contraction initiated by nerve impulse. see neurogenic.

myoglobin n. [Gr. mys, muscle; L. globus, ball] A type of hemoglobin occurring in muscle cells concerned with oxygen transport and storage; also called myohemoglobin.

myohematin, myohaematin n. [Gr. mys, muscle; haima, blood] An iron pigment said to occur in muscles; thought to be a cytochrome.

myoid a. [Gr. mys, muscle; eidos, like] Composed of muscle fibers.

myology n. [Gr. mys, muscle; logos, discourse] That branch of anatomy dealing with the arrangement of muscles.

myomere n. [Gr. mys, muscle; meros, part] A muscular seg-


myoneural junction Point of junction between a motor nerve and the muscle which it activates.

myoneure n. [Gr. mys, muscle; neuron, nerve] A motor neuron.

myonicity n. [Gr. mys, muscle] The contracting power of muscle tissue.

myophore n. [Gr. mys, muscle; pherein, to bear] (MOLL: Bi-valvia) A spoon- or sickle-shaped structure beneath the beak on the interior of the shell; functioning as a place of attachment for certain muscles.

myoplasm n. [Gr. mys, muscle; plasma, formed or molded] The contractile portion of a muscle cell.

myosin n. [Gr. mys, muscle] Muscle protein that combines with actin to form actomyosin in muscle contraction.

myostracum n. [Gr. mys, muscle; ostrakon, shell] (MOLL: Bi-valvia) That part of the shell wall secreted at the attachment of the adductor muscles.

myotasis n. [Gr. mys, muscle; tasis, tension] Muscular tonicity or tension.

myotome n. [Gr. mys, muscle; tome, to cut] A muscle segment, somite or myomere.

myrmecobiosis n. [Gr. myrmex, ant; biosis, life] A symbiotic relationship between ants; consociation.

myrmecochory n. [Gr. myrmex, ant; chorein, to spread] Active dispersion of seeds by ants.

myrmecoclepty n. [Gr. myrmex, ant; kleptes, thief] (ARTHRO: Insecta) A form of symbiosis in which the guest ant steals food from the host ant.

myrmecodomatium n.; pl. -ia [Gr. myrmex, ant; domos, house] A plant tissue cavity inhabited by ants.

myrmecole n. [Gr. myrmex, ant; L. colere, to inhabit] An organism that lives in ants' nests, but does not otherwise interact with them. see myrmecophilous.

myrmecology n. [Gr. myrmex, ant; logos, discourse] The division of entomology that studies ants.

myrmecophagous a. [Gr. myrmex, ant; phagein, to eat] Feeding on ants.

myrmecophile n. [Gr. myrmex, ant; philos, love] A symbiont of ants.

myrmecophilous a. [Gr. myrmex, ant; philos, love] Fondness of, or benefited by an association with ants. see myrme-cole.

myrmecophily n. [Gr. myrmex, ant; philos, love] (ARTHRO: Insecta) The utilization by other insects, mainly beetles, of ant colonies as domiciles and sources of food; ant symbiosis. myrmecophilous a.

myrmecophobic a. [Gr. myrmex, ant; phobeisthai, to flee] Having the ability to repel ants.

myrmecophyte n. [Gr. myrmex, ant; phyton, plant] A myrmecophilous plant that has an obligatory, mutualistic relationship with ants.

myrmecoxenes [Gr. myrmex, ant; xenos, guest] True guests of ants. see symphile.

mysis stage (ARTHRO: Crustacea) In Decapoda, a larval stage in which only the thoracopods are used in swimming and the compound eye is stalked; schizopod larva. see zoea.

mystacine a. [Gr. mystax, moustache] Bearded; having tactile hairs or vibrissae.

mystax n. [Gr. mystax, moustache] (ARTHRO: Insecta) A cluster of hairs or bristles above the mouth; beard.

mytiliform a. [L. mytilus, sea mussel; forma, shape] 1. (ARTHRO: Insecta) In aquatic Hemiptera, the shell-shaped swimming feet. 2. (MOLL: Bivalvia) Having the form of a mussel shell; mytiloid; shell shaped like the genus Mytilus.

myzesis n. [Gr. myzein, to suck] Suction or sucking.

myzorhynchus n. [Gr. myzein, to suck; rhynchos, snout] (PLATY: Cestoda) In some Tetraphyllidea, an apical stalked, sucker-like organ on the scolex.

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