Online Dictionary of Invertebrate Zoology: Complete Work - Best Text

98Maggenti and Gardnerspiracular atrium.atrial sac (ANN: Oligochaeta) In primitive moniligastrid earthworms,the spermathecal diverticulum.atrichosy n. [Gr. a, without; trichos, hair] The absence of setaedue to evolutionary regession.atrichous a. [Gr. a, without; trichos, hair] 1. Lacking flagellaor cilia. 2. (CNID) Lacking spines or barbs, i.e., isorhizas,etc.atrichous isorhiza (CNID: Hydrozoa) A small nematocyst witha smooth tubule. see holotrichous isorhiza, basitrichousisorhiza.atriobursal orifice (ARTHRO: Chelicerata) The opening of theseminal 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 capsularprostate. b. Male reproductive organ in leeches, consistingof a thin-walled bursa, a thick-walled glandular and muscularchamber and a pair of atrial cornua opening into themuscular median chamber. 3. (ARTHRO: Insecta) A specializedarea of the trachea; a. A spiracular atrium. b. The preoralcavity in certain larvae. 4. (PORIF) A cavity into whichmany exhalant systems empty and conduct the contents toone 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. atrochala.atrophy n. [Gr. a, without; trophein, to feed] Decrease in sizeof a tissue, organ, or part after full development has beenobtained; a condition induced from lack of use, pathologicalcondition or lack of nourishment. see hypertrophy.atrous a. [L. ater, black] Black in color.attachment disk (ARTHRO: Chelicerata) The series of tiny zigzaglines or spots of silk that serve to anchor the draglinesof spiders.attenuate a. [L. ad, toward; tenuis, thin] To become thin,