E - Zoological Terms

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eccrine

(Gr. ek, out of, + krinein, to separate). Applies to a type of mammalian sweat gland that produces a watery secretion.

ecdysiotropin

(Gr. ekdysis, to strip off, escape, + tropos, a turn, change). Hormone secreted in brain of insects that stimulates prothoracic gland to secrete molting hormone. Prothoracicotropic hormone; brain hormone.

ecdysis

(Gr. ekdysis, to strip off, escape). Shedding of outer cuticular layer; molting, as in insects or crustaceans.

ecdysone

(Gr. ekdysis, to strip off). Molting hormone of arthropods, stimulates growth and ecdysis, produced by prothoracic glands in insects and Y organs in crustaceans.

ecocline

(Gr. oikos, home, + klino, to slope, recline). The gradient between adjacent biomes; a gradient of environmental conditions.

ecology

(Gr. oikos, house, + logos, discourse). Part of biology that deals with the relationship between organisms and their environment.

ecosystem

(eco[logy] from Gr. oikos, house, + system). An ecological unit consisting of both the biotic communities and the nonliving (abiotic) environment, which interact to produce a stable system.

ecotone

(eco[logy] from Gr. oikos, home, + tonos, stress). The transition zone between two adjacent communities.

ectoderm

(Gr. ektos, outside, + derma, skin). Outer layer of cells of an early embryo (gastrula stage); one of the germ layers, also sometimes used to include tissues derived from ectoderm.

ectognathous

(Gr. ektos, outside, without, + gnathos, jaw). Derived character of most insects; mandibles and maxillae not in pouches.

ectolecithal

(Gr. ektos, outside, + lekithos, yolk). Yolk for nutrition of the embryo contributed by cells that are separate from the egg cell and are combined with the zygote by envelopment within the eggshell.

ectoneural

(Gr. ektos, outside, without, + neuron, nerve). Oral (chief) nervous system in echinoderms.

ectoplasm

(Gr. ektos, outside, + plasma, form). The cortex of a cell or that part of cytoplasm just under the cell surface; contrasts with endoplasm.

ectothermic

(Gr. ektos, outside, + therme, heat). Having a variable body temperature derived from heat acquired from the environment; contrasts with endothermic.

edema

(Gr. oidema, swelling). Escape of fluid from blood into interstitial space, causing swelling.

effector

(L. efficere, bring to pass). An organ, tissue, or cell that becomes active in response to stimulation.

efferent

(L. ex, out, + ferre, to bear). Leading or conveying away from some organ, for example, nerve impulses conducted away from the brain, or blood conveyed away from an organ; contrasts with afferent.

egestion

(L. egestus, to discharge). Act of casting out indigestible or waste matter from the body by any normal route.

electron

A subatomic particle with a negative charge and a mass of 9.1066 × 10−28 gram.

eleocyte

(Gr. elaion, oil, + kytos, hollow vessel). Fat-containing cells in annelids that originate from the chlorogogen tissue.

elephantiasis

Disfiguring condition caused by chronic infection with filarial worms Wuchereria bancrofti and Brugia malayi.

embryogenesis

(Gr. embryon, embryo, + genesis, origin). The origin and development of the embryo; embryogeny.

emergence

(L. e, out, + mergere, to plunge). The appearance of properties in a biological system (at the molecular, cellular, organismal, or species levels) that cannot be deduced from knowledge of the component parts taken separately or in partial combinations; such properties are termed emergent properties.

emigrate

(L. emigrare, to move out). To move from one area to another to take up residence.

emulsion

(L. emulsus, milked out). A colloidal system in which both phases are liquids.

endemic

(Gr. en, in, + demos, populace). Peculiar to a certain region or country; native to a restricted area; not introduced.

endergonic

(Gr. endon, within, + ergon, work). Used in reference to a chemical reaction that requires energy; energy absorbing.

endite

(Gr. endon, within). Medial process on an arthropod limb.

endochondral

(Gr. endon, within, + chondros, cartilage). Occurring with the substance of cartilage, especially bone formation.

endocrine

(Gr. endon, within, + krinein, to separate). Refers to a gland that is without a duct and that releases its product directly into the blood or lymph.

endocytosis

(Gr. endon, within, + kytos, hollow vessel). The engulfment of matter by phagocytosis, potocytosis, receptor-mediated endocytosis, and by bulk-phase (nonspecific) endocytosis.

endoderm

(Gr. endon, within, + derma, skin). Innermost germ layer of an embryo, forming the primitive gut; also may refer to tissues derived from endoderm.

endognathous

(Gr. endon, within, + gnathous, jaw). Ancestral character in insects, found in orders Diplura, Collembola, and Protura, in which the mandibles and maxillae are located in pouches.

endolecithal

(Gr. endon, within, + lekithos, yolk). Yolk for nutrition of the embryo incorporated into the egg cell itself.

endolymph

(Gr. endon, within, + lympha, water). Fluid that fills most of the membranous labyrinth of the vertebrate ear.

endometrium

(Gr. endon, within, + metra, womb). The mucous membrane lining the uterus.

endoplasm

(Gr. endon, within, + plasma, mold or form). The portion of cytoplasm that immediately surrounds the nucleus.

endoplasmic reticulum

A complex of membranes within a cell; may bear ribosomes (rough) or not (smooth).

endopod, endopodite

(Gr. endon, within, + pous, podos, foot). Medial branch of a biramous crustacean appendage.

endopterygote

(Gr. endon, within, + pteron, feather, wing). Insect in which the wing buds develop internally; has holometabolous metamorphosis.

endorphin

(contraction of endogenous morphine). Group of opiatelike brain neuropeptides that modulate pain perception and are implicated in many other functions.

endoskeleton

(Gr. endon, within, + skeletos, hard). A skeleton or supporting framework within the living tissues of an organism; contrasts with exoskeleton.

endosome

(Gr. endon, within, + soma, body). Nucleolus in nucleus of some protozoa that retains its identity through mitosis.

endostyle

(Gr. endon, within, + stylos, a pillar). Ciliated groove(s) in the floor of the pharynx of tunicates, cephalochordates, and larval jawless fishes useful for accumulating and moving food particles to the stomach.

endothelium

(Gr. endon, within, + thele, nipple). Squamous epithelium lining internal body cavities such as heart and blood vessels. Adj., endothelial.

endothermic

(Gr. endon, within, + therme, heat). Having a body temperature determined by heat derived from the animal’s own oxidative metabolism; contrasts with ectothermic.

enkephalin

(Gr. endon, within, + kephale, head). Group of small brain neuropeptides with opiate-like qualities.

enterocoel

(Gr. enteron, gut, + koilos, hollow). A type of coelom formed by the outpouching of a mesodermal sac from the endoderm of the primitive gut.

enterocoelic

mesoderm formation Embryonic formation of mesoderm by a pouchlike outfolding from the archenteron, which then expands and obliterates the blastocoel, thus forming a large cavity, the coelom, lined with mesoderm.

enterocoelomate

(Gr. enteron, gut, + koiloma, cavity, + Eng. ate, state of). An animal having an enterocoel, such as an echinoderm or a vertebrate.

enteron

(Gr. intestine). The digestive cavity.

entomology

(Gr. entoma, an insect, + logos, discourse). Study of insects.

entozoic

(Gr. entos, within, + zoon, animal). Living within another animal; internally parasitic (chiefly parasitic worms).

entropy

(Gr. en, in, on, + tropos, turn, change in manner). A quantity that is the measure of energy in a system not available for doing work.

enzyme

(Gr. enzymos, leavened, from en, in, + zyme, leaven). A substance, produced by living cells, that is capable of speeding up specific chemical transformations, such as hydrolysis, oxidation, or reduction, but is unaltered itself in the process; a biological catalyst.

eocytes

(Gr. eos, the dawn, + kytos, hollow vessel). A group of prokaryotes currently classified among the Archaebacteria but possibly a sister group of eukaryotes.

ephyra

(Gr. Ephyra, Greek city). Refers to castlelike appearance. Medusa bud from a scyphozoan polyp.

epidermis

(Gr. epi, on, upon, + derma, skin). The outer, nonvascular layer of skin of ectodermal origin; in invertebrates, a single layer of ectodermal epithelium.

epididymis

(Gr. epi, on, upon, + didymos, testicle). Part of the sperm duct that is coiled and lying near the testis.

epigenesis

(Gr. epi, on, upon, + genesis, birth). The embryological (and generally accepted) view that an embryo is a new creation that develops and differentiates step by step from an initial stage; the progressive production of new parts that were nonexistent as such in the original zygote.

epigenetics

(Gr. epi, on, upon, + genesis, birth). Study of the relationship between genotype and phenotype as mediated by developmental processes.

epipod, epipodite

(Gr. epi, on, upon, + pous, podos, foot). A lateral process on the protopod of a crustacean appendage, often modified as a gill.

epistasis

(Gr. epi, on, upon, + stasis, standing). Prevention of expression of an allele at one locus by an allele at another locus.

epistome

(Gr. epi, on, upon, + stoma, mouth). Flap over the mouth in some lophophorates bearing the protocoel.

epithelium

(Gr. epi, on, upon, + thele, nipple). A cellular tissue covering a free surface or lining a tube or cavity.

epitoke

(Gr. epitokos, fruitful). Posterior part of a marine polychaete when swollen with developing gonads during the breeding season; contrast with atoke.

epitope

That portion of an antigen to which an antibody or T-cell receptor binds. Also called antigenic determinant.

erythroblastosis fetalis

(Gr. erythros, red, + blastos, germ, + osis, a disease; L. fetalis, relating to a fetus). A disease of newborn infants caused when Rh-negative mothers develop antibodies against the Rh-positive blood of the fetus. See blood type.

erythrocyte

(Gr. erythros, red, + kytos, hollow vessel). Red blood cell; has hemoglobin to carry oxygen from lungs or gills to tissues; during formation in mammals, erythrocytes lose their nuclei, those of other vertebrates retain the nuclei.

esthete

(Gr. esthes, a garment). Light sensory receptor on a shell of a chiton (phylum Mollusca).

estrus

(L. oestrus, gadfly, frenzy). The period of heat, or rut, especially of the female during ovulation of the egg. Associated with maximum sexual receptivity. estuary (es+ch‰-we+re) (L. aestuarium, estuary). An arm of the sea where the tide meets the current of a freshwater drainage.

ethology

(Gr. ethos, character, + logos, discourse). The study of animal behavior in natural environments.

euchromatin

(Gr. eu, good, well, + chroma, color). Part of the chromatin that takes up stain less than heterochromatin, contains active genes.

eukaryotic, eucaryotic

(Gr. eu, good, true, + karyon, nut, kernel). Organisms whose cells characteristically contain a membrane-bound nucleus or nuclei; contrasts with prokaryotic.

euploidy

(Gr. eu, good, well, + ploid, multiple of). Change in chromosome number from one generation to the next in which there is an addition or deletion of a complete set of chromosomes in the progeny; the most common type is polyploidy.

euryhaline

(Gr. eurys, broad, + hals, salt). Able to tolerate wide ranges of saltwater concentrations.

euryphagous

(Gr. eurys, broad, + phagein, to eat). Eating a large variety of foods.

eurytopic

(Gr. eurys, broad, + topos, place). Refers to an organism with a wide environmental range.

eutely

(Gr. euteia, thrift). Condition of a body composed of a constant number of cells or nuclei in all adult members of a species, as in rotifers, acanthocephalans, and nematodes.

evagination

(L. e, out, + vagina, sheath). An outpocketing from a hollow structure.

evolution

(L. evolvere, to unfold). Organic evolution encompasses all changes in the characteristics and diversity of life on earth throughout its history.

evolutionary

duration

The length of time that a species or higher taxon exists in geological time.

evolutionary species concept

A single lineage of ancestral-descendant populations that maintains its identity from other such lineages and has its own evolutionary tendencies and historical fate; differs from the biological species concept by explicitly including a time dimension and including asexual lineages.

evolutionary taxonomy

A system of classification, formalized by George Gaylord Simpson, that groups species into Linnean higher taxa representing a hierarchy of distinct adaptive zones; such taxa may be monophyletic or paraphyletic but not polyphyletic.

excision repair

Means by which cells are able to repair certain kinds of damage (dimerized pyrimidines) in their DNA.

exergonic

(Gr. exo, outside of, + ergon, work). An energy-yielding reaction.

exite

(Gr. exo, outside). Process from lateral side of an arthropod limb.

exocrine

(Gr. exo, outside, + krinein, to separate). A type of gland that releases its secretion through a duct; contrasts with endocrine.

exocytosis

(Gr. exo, outside, + kytos, hollow vessel). Transport of a substance from inside a cell to the outside.

exon

(Gr. exo, outside). Part of the mRNA as transcribed from the DNA that contains a portion of the information necessary for final gene product.

exopod, exopodite

(Gr. exo, outside, + pous, podos, foot). Lateral branch of a biramous crustacean appendage.

exopterygote

(Gr. exo, without, + pteron, feather, wing). Insect in which the wing buds develop externally during nymphal instars; has hemimetabolous metamorphosis.

exoskeleton

(Gr. exo, outside, + skeletos, hard). A supporting structure secreted by ectoderm or epidermis; external, not enveloped by living tissue, as opposed to endoskeleton.

experiment

A trial made to support or disprove a hypothesis.

exteroceptor

(L. exter, outward, + capere, to take). A sense organ excited by stimuli from the external world.

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