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

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T cell

A type of lymphocyte important in cellular immune response and in regulation of most immune responses.

T-cell receptors

Receptors borne on surfaces of T cells. The variable region of a T-cell receptor binds with a specific antigen.


(L. tactilis, able to be touched, from tangere, to touch). Pertaining to touch.


, pl. tagmata (Gr. tagma, arrangement, order, row). A compound body section of an arthropod resulting from embryonic fusion of two or more segments; for example, head, thorax, abdomen.

tagmatization, tagmosis

Organization of the arthropod body into tagmata.


(Russ.). Habitat zone characterized by large tracts of coniferous forests, long, cold winters, and short summers; most typical in Canada and Siberia.


(Gr. tantulus, so small). Larva of a tantulocaridan (subphylum Crustacea).


pl. taxes (Gr. taxis, arrangement). An orientation movement by a (usually) simple organism in response to an environmental stimulus.


pl. taxa (Gr. taxis, arrangement). Any taxonomic group or entity.


(Gr. taxis, arrangement, + nomos, law). Study of the principles of scientific classification; systematic ordering and naming of organisms.


(L. roof). A rooflike structure, for example, dorsal part of capitulum in ticks and mites.


(L. tegmen, a cover). External epithelium of crinoids (phylum Echinodermata).


(L. tegumentum, from tegere, to cover). An integument: specifically external covering in cestodes and trematodes, formerly believed to be a cuticle.


(Gr. telos, end, + encephalon, brain). The most anterior vesicle of the brain; the anteriormost subdivision of the prosencephalon that becomes the cerebrum and associated structures.


(Gr. telos, end, + L. logia, study of, from Gr. logos, word). The philosophical view that natural events are goal directed and are preordained, as opposed to the scientific view of mechanical determinism.


(Gr. telos, end, + kentron, center). Chromosome with centromere at the end.


(Gr. telos, end, + lekithos, yolk, + al). Having the yolk concentrated at one end of an egg.


(Gr. telson, extremity). Posterior projection of the last body segment in many crustaceans.


(Gr. temno, to cut, + spondylos, vertebra). A large lineage of amphibians that extended from the Carboniferous to the Triassic.


A pattern or mold guiding the formation of a duplicate; often used with reference to gene duplication.


(L. tendo, tendon). Fibrous band connecting muscle to bone or other movable structure.


(L. tentaculum, feeler, + kystis, pouch). One of the sense organs along the margin of medusae; a rhopalium.


(L. back). Dorsal part of an arthropod body segment.


(L. territorium, from terra, earth). A restricted area preempted by an animal or pair of animals, usually for breeding purposes, and guarded from other individuals of the same species.


(L. testa, shell). A shell or hardened outer covering.


(Gr. tetras, four). Group of two pairs of chromatids at synapsis and resulting from the replication of paired homologous chromosomes; the bivalent.


(Gr. tetras, four, + pous, podos, foot). Four-footed vertebrates; the group includes amphibians, reptiles, birds, and mammals.


(Gr. theke, box, + odontos, tooth). A large assemblage of Triassic archosaurian diapsids of the order Thecodontia and characterized by having teeth set in sockets.


(Gr. theraps, an attendant). Extinct Mesozoic mammal-like reptiles from which true mammals evolved.


(Gr. therme, heat, + klinein, to swerve). Layer of water separating upper warmer and lighter water from lower colder and heavier water in a lake or sea; a stratum of abrupt change in water temperature.


(L. thorax, chest). Pertaining to the thorax or chest.


Enzyme catalyzing fibrinogen transformation into fibrin. Percursor is prothrombin

Tiedemann's bodies

(from F. Tiedemann, German anatomist). Four or five pairs of pouchlike bodies attached to the ring canal of sea stars, apparently functioning in production of coelomocytes.

tight junction

Region of actual fusion of cell membranes between two adjacent cells.


(M.E. tissu, tissue). An aggregation of cells, usually of the same kind, organized to perform a common function.


(Fr. titrer, to titrate). Concentration of a substance in a solution as determined by titration.


(L. tornare, to turn). A free-swimming larva of enteropneusts that rotates as it swims; resembles somewhat the bipinnaria larva of echinoderms.


(L. torquere, to twist). A twisting phenomenon in gastropod development that alters the position of the visceral and pallial organs by 180 degrees.


(Gr. toxikon, poison, + kystis, bladder). Structures possessed by predatory ciliate protozoa, which on stimulation expel a poison to subdue the prey.

trabecular net

(L. trabecula, a small beam). Network of living tissue formed by pseudopodia of amebocytes in Hexactinellida (phylum Porifera).


(M.L. windpipe). The windpipe. Also, any of the air tubes of insects.


Formation of messenger RNA from the coded DNA.


Condition in which bacterial DNA (and the genetic characteristics it bears) is transferred from one bacterium to another by the agent of viral infection.

transfer RNA (tRNA)

A form of RNA of about 70 or 80 nucleotides, which are adapter molecules in the synthesis of proteins. A specific amino acid molecule is carried by transfer RNA to a ribosome-messenger RNA complex for incorporation into a polypeptide.


Condition in which DNA in the environment of bacteria somehow penetrates them and is incorporated into their genetic complement, so that their progeny inherit the genetic characters so acquired.


(L. a transferring). The process in which the genetic information present in messenger RNA is used to direct the order of specific amino acids during protein synthesis.


See permease

transverse plane

(L. transversus, across). A plane or section that lies or passes across a body or structure.


Disease caused by infection with the nematode Trichinella spiralis.


(Gr. thrix, hair, + kystis, bladder). Sac-like protrusible organelle in the ectoplasm of ciliates, which discharges as a threadlike weapon of defense.


(Gr. tria, three, + glykys, sweet, + ide, suffix denoting compound). A triester of glycerol with one, two, or three acids.


(Gr. treis, three, + meros, a part). Body in three main divisions, as in lophophorates and some deuterostomes.


See trimerous.


(Gr. triploos, triple, + blastos, germ). Pertaining to metazoa in which the embryo has three primary germ layers - ectoderm, mesoderm, and endoderm.

trisomy 21

See Down syndrome.


(Gr. trochos, wheel, + pherein, to bear). A free-swimming ciliated marine larva characteristic of most molluscs and certain ectoprocts, brachiopods, and marine worms; an ovoid or pyriform body with preoral circlet of cilia and sometimes a secondary circlet behind the mouth.


(Gr. trophe, food, + allaxis, barter, exchange). Exchange of food between young and adults, especially certain social insects.


(Gr. trophos, one who feeds). Jaw-like structures in the mastax of rotifers.


(Gr. trophe, food). Pertaining to feeding and nutrition.


(Gr. trephein, to nourish, + blastos, germ). Outer ectodermal nutritive layer of blastodermic vesicle; in mammals it is part of the chorion and attaches to the uterine wall.


(Gr. trophe, food, + soma, body). Organ in poganophorans bearing mutualistic bacteria, derived from midgut.


(Gr. trophe, food, + zoon, animal). Adult stage in the life cycle of a protozoan in which it is actively absorbing nourishment.


(Gr. trope, to turn toward). Related to the tropics (tropical); in endocrinology, a hormone that influences the action of another hormone or endocrine gland (usually pronounced tro´pic).


(Gr. tropos, turn, + mys, muscle). Low-molecular weight protein surrounding the actin filaments of striated muscle.


Complex of globular proteins positioned at intervals along the actin filament of skeletal muscle; thought to serve as a calcium-dependent switch in muscle contraction.

tube feet (podia)

Numerous small, muscular, fluid-filled tubes projecting from body of echinoderms; part of water-vascular system; used in locomotion, clinging, food handling, and respiration.


(L. tuberculum, small hump). Small protuberance, knob, or swelling.


(L. tubulus, small tube, + in, belonging to). Globular protein forming the hollow cylinder of microtubules.

tumor necrosis factor

A cytokine, the most important source of which is macrophages, that is a major mediator of inflammation.

tumor suppressor gene

A gene whose products act as restraints on cell division by triggering apoptosis, controlling transcription of other genes, restraining progression in phases of the cell cycle, or by other means.


(Russ. from Lapp, tundar, hill). Terrestrial habitat zone, located between taiga and polar regions; characterized by absence of trees, short growing season, and mostly frozen soil during much of the year.


(L. tunica, tunic, coat). In tunicates, a cuticular, cellulose-containing covering of the body secreted by the underlying body wall.


(Gr. tympanon, drum). Relating to the tympanum that separates the outer and middle ear (eardrum).

type specimen

A specimen deposited in a museum that formally defines the name of the species that it represents.


(Gr. typhlos, blind, + solen, channel, pipe). A longitudinal fold projecting into the intestine in certain invertebrates such as the earthworm.


(L. typus, image). A classification of organisms in which members of a taxon are perceived to share intrinsic, essential properties, and variation among organisms is regarded as uninteresting and unimportant.

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