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  Section: Zoological Terms used in General Zoology
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H - Zoological Terms

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(L. habitare, to dwell). The place where an organism normally lives or where individuals of a population live.


A kind of learning in which continued exposure to the same stimulus produces diminishing responses.


pl. halteres (hal-ti+rez) (Gr. leap). In Diptera, small club-shaped structure on each side of the metathorax representing the hindwings; believed to be sense organs for balancing; also called balancer.


(Gr. haploos, single, + diploos, double, + eidos, form). Reproduction in which haploid males are produced parthenogenetically, and diploid females are from fertilized eggs.


(Gr. haploos, single). The reduced, or n, number of chromosomes, typical of gametes, as opposed to the diploid, or 2n, number found in somatic cells. In certain groups, mature organisms may have a haploid number of chromosomes.

Hardy-Weinberg equilibrium

Mathematical demonstration that the Mendelian hereditary process does not change the populational frequencies of alleles or genotypes across generations, and that change in allelic or genotypic frequencies requires factors such as natural selection, genetic drift in finite populations, recurring mutation, migration of individuals among populations, and nonrandom mating.


(Gr. hekaton, hundred, + kotyle, cup). Specialized, and sometimes autonomous, arm that serves as a male copulatory organ in cephalopods.

hemal system

(Gr. haima, blood). System of small vessels in echinoderms; function unknown.


(Gr. haima, blood, + erythros, red). A red, ironcontaining respiratory pigment found in the blood of some polychaetes, sipunculids, priapulids, and brachiopods.


(Gr. hemi, half, + metabole, change). Refers to gradual metamorphosis during development of insects, without a pupal stage.


(Gr. haima, blood, + koiloma, cavity). Major body space in arthropods replacing the coelom, contains the blood (hemolymph).


(Gr. haima, blood, + L. globulus, globule). An iron-containing respiratory pigment occurring in vertebrate red blood cells and in blood plasma of many invertebrates; a compound of an iron porphyrin heme and globin proteins.


(Gr. haima, blood, + L. lympha, water). Fluid in the coelom or hemocoel of some invertebrates that represents the blood and lymph of vertebrates.


(Gr. haima, blood, + zoon, an animal). Insoluble digestion product of malaria parasites produced from hemoglobin.


(Gr. hepatikos, of the liver). Pertaining to the liver.


(L. herba, green crop, + vorare, to devour). Any organism subsisting on plants. Adj., herbivorous.


(L. heres, heir). The faithful transmission of biological traits from parents to their offspring.


(Gr. hermaphroditos, containing both sexes; from Greek mythology, Hermaphroditos, son of Hermes and Aphrodite). An organism with both male and female functional reproductive organs.
Hermaphroditism may refer to an aberration in unisexual animals; monoe cyimplies that this is the normal condition for the species.


(Gr. herma, reef, + typos, pattern). Relating to reef-forming corals.


(Gr. heteros, different, + kerkos, tail). In some fishes, a tail with the upper lobe larger than the lower, and the end of the vertebral column somewhat upturned in the upper lobe, as in sharks.


(Gr. heteros, different, + chroma, color). Chromatin that stains intensely and appears to represent inactive genetic areas.


(Gr. heteros, different, + chronos, time). Evolutionary change in the relative time of appearance or rate of development of characteristics from ancestor to descendant.


(Gr. heteros, different, + odous, tooth). Having teeth differentiated into incisors, canines, and molars for different purposes.


(Gr. heteros, different, + trophos, feeder). An organism that obtains both organic and inorganic raw materials from the environment in order to live; includes most animals and those plants that do not carry on photosynthesis.


(Gr. heteros, different, + zygotos, yoked). An organism in which homologous chromosomes contain different allelic forms (often dominant and recessive) of a locus; derived from a zygote formed by union of gametes of dissimilar allelic constitution.


(Gr. hex, six, + meros, part). Six parts, specifically, symmetry based on six or multiples thereof.


(L. hibernus, wintry). Condition, especially of mammals, of passing the winter in a torpid state in which the body temperature drops nearly to freezing and the metabolism drops close to zero.

hierarchical system

A scheme arranging organisms into a series of taxa of increasing inclusiveness, as illustrated by Linnean classification.


(Gr. histos, tissue, + genesis, descent). Formation and development of tissue.


(Gr. histos, tissue). Any of several simple proteins found in cell nuclei and complexed at one time or another with DNA. Histones yield a high proportion of basic amino acids on hydrolysis; characteristic of eukaryotes.

holoblastic cleavage

(Gr. holo, whole, + blastos, germ). Complete and approximately equal division of cells in early embryo. Found in mammals, amphioxus, and many aquatic invertebrates that have eggs with a small amount of yolk.


(Gr. holo, complete, + metabole, change). Complete metamorphosis during development.

holophytic nutrition

(Gr. holo, whole, + phyt, plant). Occurs in green plants and certain protozoa and involves synthesis of carbohydrates from carbon dioxide and water in the presence of light, chlorophyll, and certain enzymes.

holozoic nutrition

(Gr. holo, whole, + zoikos, of animals). Type of nutrition involving ingestion of liquid or solid organic food particles.

home range

The area over which an animal ranges in its activities. Unlike territories, home ranges are not defended.


(Gr. homoios, like, resembling, + L. buxus, boxtree [used in the sense of enclosed, contained]). A highly conserved 180-base pair sequence found in regulatory sequences of protein-coding genes that regulate development.


(Gr. homeo, alike, + stasis, state or standing). Maintenance of an internal steady state by means of self-regulation.


(Gr. homeo, alike, + therme, heat). Having a nearly uniform body temperature, regulated independent of the environmental temperature; “warm blooded.”

homeotic genes

(Gr. homoios, like, resembling). Genes, identified through mutations, that give developmental identity to specific body segments.


(L. homo, hominis, man). A member of the family Hominidae, now represented by one living species, Homo sapiens.


Relating to the Hominoidea, a superfamily of primates to which the great apes and humans are assigned.


(Gr. homos, same, common, + kerkos, tail). A tail with the upper and lower lobes symmetrical and the vertebral column ending near the middle of the base, as in most telost fishes.


(Gr. homos, same, + odous, tooth). Having all teeth similar in form.


See allograft


(Gr. homologos, agreeing). Similarity of parts or organs of different organisms caused by evolutionary derivation from a corresponding part or organ in a remote ancestor, and usually having a similar embryonic origin. May also refer to a matching pair of chromosomes. Serial homology is the correspondence in the same individual of repeated structures having the same origin and development, such as the appendages of arthropods. Adj., homologous


Phenotypic similarity among characteristics of different species or populations (including molecular, morphological, behavioral or other features) that does not accurately represent patterns of common evolutionary descent (= nonhomologous similarity); it is produced by evolutionary parallelism, convergence and/or reversal, and is revealed by incongruence among different characters on a cladogram or phylogenetic tree.


(Gr. homos, same, + zygotos, yoked). An organism having identical alleles at one or more genetic loci. Adj., homozygous.


(L. humor, a fluid). Pertaining to an endocrine secretion.

humoral immune response

Immune response involving production of antibodies, specifically the TH2 arm of the immune response. Contrast cell-mediated immune response


(Gr. hyalos, glass). Adj., glassy, translucent. Noun, a clear, glassy, structureless material occurring, for example, in cartilage, vitreous body, mucin, and glycogen.


(contraction of hybrid + myeloma). Fused product of a normal and a myeloma (cancer) cell, which has some of the characteristics of the normal cell.

hydatid cyst

(Gr. hydatis, watery vesicle). A type of cyst formed by juveniles of certain tapeworms (Echinococcus) in their vertebrate hosts.


(Gr. hydor, water, + anthos, flower). Nutritive zooid of hydroid colony.


(Gr. hydor, water, + kaulos, stem of a plant). Stalks or “stems” of a hydroid colony, the parts between the hydrorhiza and the hydranths.


(Gr. hydor, water, + koilos, hollow). Second or middle coelomic compartment in echinoderms; left hydrocoel gives rise to water vascular system.


Members of phylum Cnidaria, class Hydrozoa, with massive calcareous skeletons.

hydrogen bond

A relatively weak chemical bond resulting from unequal charge distribution within molecules, in which a hydrogen atom covalently bonded to another atom is attracted to the electronegative portion of another molecule.


The polyp form of a cnidarian as distinguished from the medusa form. Any cnidarian of the class Hydrozoa, order Hydroida.


(Gr. hydor, water, + lysis, a loosening). The decomposition of a chemical compound by the addition of water; the splitting of a molecule into its groupings so that the split products acquire hydrogen and hydroxyl groups.


(Gr. hydor, water, + rhiza, a root). Rootlike stolon that attaches a hydroid to its substrate.


(Gr. hydor, water, + sphaira, ball, sphere). Aqueous envelope of the earth.

hydrostatic pressure

The pressure exerted by a fluid (gas or liquid), defined as force per unit area. For example, the hydrostatic pressure of one atmosphere (1 atm) is 14.7 lb/in2.

hydrostatic skeleton

A mass of fluid or plastic parenchyma enclosed within a muscular wall to provide the support necessary for antagonistic muscle action; for example, parenchyma in acoelomates and perivisceral fluids in pseudocoelomates serve as hydrostatic skeletons.

hydrothermal vent

A submarine hot spring; seawater seeping through the sea bottom is heated by magma and expelled back into the sea through the hydrothermal vent.


(hydrogen + oxygen, + yl). Containing an OH group, a negatively charged ion formed by alkalies in water.


(Gr. hyoeides [shaped like the Gr. letter upsilon Y, + eidos, form], + L. mandere, to chew). Bone derived from the hyoid gill arch, forming part of articulation of the lower jaw of fishes, and forming the stapes of the ear of amniotic vertebrates.


(Gr. hyper, over, + osmos, impulse). Refers to a solution whose osmotic pressure is greater than that of another solution to which it is compared; contains a greater concentration of dissolved particles and gains water through a selectively permeable membrane from a solution containing fewer particles; contrasts with hypoosmotic


(Gr. hyper, over, + para, beside, + sitos, food). Parasitism of a parasite by another parasite.


(Gr. hyper, over, + trophe, nourishment). Abnormal increase in size of a part or organ.


(Gr. hypo, under, + L. dermis, skin). The cellular layer lying beneath and secreting the cuticle of annelids, arthropods, and certain other invertebrates.


(Gr. hypo, under, + osmos, impulse). Refers to a solution whose osmotic pressure is less than that of another solution with which it is compared or taken as a standard, contains a lesser concentration of dissolved particles and loses water during osmosis; contrasts with hyperosmotic.


(Gr. hypo, under, + physis, growth). Pituitary body.


(Gr. hypo, under, + stoma, mouth). Name applied to structure in various invertebrates (such as mites and ticks), located at posterior or ventral area of mouth.


(Gr. hypo, under, + thalamos, inner chamber). A ventral part of the forebrain beneath the thalamus; one of the centers of the autonomic nervous system.


(Gr. hypothesis, foundation, supposition). A statement or proposition that can be tested by experiment. hypothetico-deductive (Gr. hypotithenai, to suppose, + L. deducere, to lead). Scientific process of making a conjecture and then seeking empirical tests that potentially lead to its rejection.

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