athermobiosis n. [Gr. a, without; thermos, hot; biosis, manner of life] 1. Dormancy induced by low temperatures in relation to an organism. 2. The process of waste elimination during a resting stage at low temperature.
athrocyte n. [Gr. athroos, collected; kytos, container] A sessile type of coelomocyte, phagocytic in function.
athrocytosis n. [Gr. athroos, collected; kytos, container] The ability of cells to absorb and retain particles in suspension.
atmosphere n. [Gr. atmos, vapor; sphaira, ball] 1. The outer circle of an ocellate spot. 2. The envelope of air around earth that supports life.
atoke n. [Gr. a, without; tokos, birth] (ANN: Polychaeta) The anterior sexless portion of certain marine worms. atokous a. see epitoke.
atoll n. [Mal. atoll] A circular coral reef surrounding a central lagoon.
atom n. [L. atomus, a small particle] 1. Any extremely small particle, dot or point. 2. An elementary particle which enters into a chemical reaction.
ATP adenosine triphosphate atracheate a. [Gr. a, without; trachia, windpipe] Without tracheae, or visible constriction between head and prothorax.
atractoid a. [Gr. atraktos, spindle; eidos, form] Pertaining to spindle-shaped; fusiform.
atrial a. [L. atrium, vestibule] 1. Of or pertaining to an atrium. 2. (ANN) Referring to glandular tissue associated with a cleft or coelomic invagination containing the male pore.
atrial bag (bryo) That part of a polypidian vesicle attached to the frontal wall of a developing zooid, from which the tentacle sheath is formed.
atrial cavity In procordates, a cavity located between the pharynx and the body wall.
atrial cornua (ANN: Hirudinoidea) Horns or hornlike prolongations of the atrium.
atrial gland (ANN) Prostates without stalks.
atrial orifice (ARTHRO: Insecta) The exterior opening of the spiracular atrium.
atrial sac (ANN: Oligochaeta) In primitive moniligastrid earthworms, the spermathecal diverticulum.
atrichosy n. [Gr. a, without; trichos, hair] The absence of setae due to evolutionary regession.
atrichous a. [Gr. a, without; trichos, hair] 1. Lacking flagella or cilia. 2. (CNID) Lacking spines or barbs, i.e., isorhizas, etc.
atrichous isorhiza (CNID: Hydrozoa) A small nematocyst with a smooth tubule. see holotrichous isorhiza, basitrich-ous isorhiza.
atriobursal orifice (ARTHRO: Chelicerata) The opening of the seminal receptacle of female spiders.
atrium n.; pl. atria [L. atrium, vestibule] 1. A cavity, division, entrance or passageway of various invertebrates. 2. (Ann) a. A diverticulum of the spermatheca; a tubular or capsular prostate. b. Male reproductive organ in leeches, consisting of a thin-walled bursa, a thick-walled glandular and muscular chamber and a pair of atrial cornua opening into the muscular median chamber. 3. (ARTHRO: Insecta) A specialized area of the trachea; a. A spiracular atrium. b. The pre-oral cavity in certain larvae. 4. (PORIF) A cavity into which many exhalant systems empty and conduct the contents to one or more usually terminal ocules. atriate a.
atrium oris (ARTHRO: Crustacea) The preoral cavity.
atrocha n. [Gr. a, without; trochos, wheel] (ANN: Polychaeta) A uniformly ciliated larva, lacking the preoral band. atro-chal a.
atrophy n. [Gr. a, without; trophein, to feed] Decrease in size of a tissue, organ, or part after full development has been obtained; a condition induced from lack of use, pathological condition or lack of nourishment. see hypertrophy.
attachment disk (ARTHRO: Chelicerata) The series of tiny zigzag lines or spots of silk that serve to anchor the draglines of spiders.
attenuate a. [L. ad, toward; tenuis, thin] To become thin, slender, fine, extended, growing narrower, tapering.
attingent a. [L. attignus, touching] Touching, making contact.
attitude n. [L. aptus, suited] The posture or expression assumed by an organism.
attractant n. [L. ad, toward; tractus, draw] A chemical substance causing positive behavorial responses. see phero-mone.
attractor epimeralis muscle (ARTHRO: Crustacea) In Deca-poda, a prominent muscle inserting along the line of the brachiocardiac groove.
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