Tetractine see tetraxon

tetrad n. [Gr. tetra, four; -ad, collective noun] Any set of four.

tetradelphic a. [Gr. tetra, four; delphys, womb] (NEMATA) Having four uteri.

tetramerous a. [Gr. tetra, four; meros, part] 1. Having a four jointed tarsus. 2. Having body parts arranged in fours.

tetramorphic a. [Gr. tetra, four; morphe, form] (CNID: Hydro-zoa) Having four distinct forms in one individual.

tetraploid n. [Gr. tetraple, fourfold; eidos, like] A polyploid with four haploid chromosome sets.

tetrapod n. [Gr. tetra, four; pous, foot] Having 2 pair of legs. see bipod.

tetrapterous a. [Gr. tetra, four; pteron, wing] Having 4 wings.

tetrasomic a. [Gr. tetra, four; soma, body] Polysomic cells with one chromosome represented 4 times in a normal diploid; 2n+2.

tetrathyridium n. [Gr. tetra, four; thyridion, window] (PLATY: Cestoda) A cysticercoid of Mesocestoides which has a solid body and a scolex not surrounded by special membranes. tetrathyridial a.

tetraxon n. [Gr. tetra, four; axon, axis] (PORIF) A spicule of 4 equal and similar rays meeting at equal angles; tetractine; quadriradiate. tetraxonid a.

thalassophilous a. [Gr. thalassa, sea; philos, loving] Inhabiting or dwelling in the sea; pelagic; thalassic.

thallus n. [Gr. thallos, young shoot] The body or colony of a compound animal.

thamnophilous a. [Gr. thamnos, shrub; philos, loving] Inhabiting thickets or dense shrubbery.

thanatocoenosis n. [Gr. thanatos, death; koinos, common] An assemblage of fossils comprised of the remains of organisms brought together after death. see biocenosis.

thanatosis n. [Gr. thanatos, death] Feigning death; letisimu-lation.

theca n.; pl. thecae [Gr. theke, case] 1. A sheath or sac-like covering or structure for an organ or organisms, as proboscis, tubes, shells, pupa or larvae. 2. (ANN: Oligochaeta) Spermatheca. 3. (ARTHRO: Insecta) A fold or sheath from phallobase enclosing the aedeagus. 4. (echinod: Cri-noidea) The skeleton. thecal, thecate a.

thelycum n. [Gr. thelykos, feminine] (ARTHRO: Crustacea) In some female Decapoda, an external pocket on the ventral side of the thorax, functioning as a seminal receptacle.

thelygenous a. [Gr. thelys, female; genes, producing] Producing mostly or only female offspring; arrhenogenous. thelygenesis n.

thelyotoky n. [Gr. thelys, female; tokos, offspring] A type of parthenogenesis in which unfertilized eggs develop into females; thelytoica. thelyotokous a. see arrenotoky, deuterotoky, amphitoky.

theory of probabilities A mathematical theory used by tax-onomists, whereby they assume that no two individuals will simultaneously have the same combination of characters as those of a given species; in mathematics, the theory of chance.

thermocline n. [Gr. therme, heat; klinein, to slope] In the strata of rapidly changing temperatures in lakes, the narrow dividing stratum between the epilimnion and hypolimnion.

thermophile n. [Gr. therme, heat; philos, loving] Living at high temperatures; hot springs fauna.

thermophobe n. [Gr. therme, heat; phobos, hate] An organism that lives at low tempertures.

thermoreceptor n. [Gr. therme, heat; L. recipere, to receive] A sensory receptor that reacts to temperature stimuli.

thermotaxis n. [Gr. therme, heat; taxis, arrangement] A taxis in which heat is the response initiating stimulus; regulation of body temperature.

thesocytes n.pl. [Gr. thesis, deposit; kytos container] (PORIF) In hibernating fresh water sponge gemmules, binucleate, highly vitelline archaeocytes.

thickener cells (PORIF) Cells influencing ray thickness during secretion of calcareous spicules.

thickness n. [A.S. thicce, thick] (MOLL: Bivalvia) 1. See inflation. 2. Measurement from the inner to outer shell surface.

thigmotaxis n.; pl. taxes [Gr. thigma, touch; taxis, arrangement] The taxis of contact; stereotaxis. a. Positive thigmotaxis: toward the contact. b. Negative thigmotaxis: away from the contact. thigmotactic a.

thigmotropism n. [Gr. thigma, touch; tropos, turn] Tropism in which direction is determined by contact with a solid body; stereotropism.

third axillary (ARTHRO: Insecta) A Y-shaped sclerite of the wing, with a flexor muscle inserted into the crotch of the Y and usually articulating with the posterior notal process and a group of anal veins.

third-form reproductive (ARTHRO: Insecta) In Isoptera, an ergatoid reproductive; a tertiary reproductive.

thoracic a. [Gr. thorax, chest] Associated with the thorax.

thoracic ganglia (ARTHRO: Insecta) The first three ganglia of the ventral nerve cord, one in each thoracic segment, controlling the locomotory organs.

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