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.
Was this article helpful?