Online Dictionary of Invertebrate Zoology: Complete Work - Best Text

Online Dictionary of Invertebrate Zoology 73sinus.anucleate a. [Gr. an, without; L. nucleus, kernel] Lacking anucleus.anural a. [Gr. an, without; oura, tail] Lacking a tail.anuria n. [Gr. an, without; ouron, urine] Absence of or inabilityto excrete urine.anus n. [L. anus] The terminal orifice of the alimentary canal,through which unabsorbed food and waste products arevoided; in some groups it is associated with the cloaca. seeuropore.aorta n. [Gr. aorte, the great artery] The main vessel carryingblood from the heart; the dorsal blood vessel.aortal chamber The thoracic expansion of the aorta.aortic valve The closure mechanism of the dorsal vessel,separating the aorta and the heart proper.apatetic color Those colors that enable an organism to mimiceither its environment or another species.apertum n. [L. aperire, to open] (ARTHRO: Insecta) In Coleoptera,a basal cell opening on the hind wing.apertural a. [L. aperire, to open] Pertaining to or on the sameside as the aperture.apertural muscle (BRYO: Gymnolaemata) One of either twopairs of muscles of cheilostomate autozooids, the occlusormuscle of the operculum or the diaphragmatic dilator muscle.aperture n. [L. aperire, to open] 1. An opening or hole, cleft,or gap. 2. (ARTHRO: Crustacea) The postero-ventral openinginto the mantle cavity of barnacles. see orifice. 3.(BRYO: Stenolaemata) The terminal skeletal opening of azooid. 4. (MOLL) An opening at the last-formed margin of ashell, providing the outlet for the head-foot mass.apex n.; pl. apexes, apices [L. apex, tip] 1. That portion ofany structure opposite the base of attachment; the tip. 2.(ARTHRO: Crustacea) The upper angle of the scutum or tergumof certain barnacles. 3. (ARTHRO: Insecta) Wing tip. 4.(MOLL) a. In Polyplacophora, the beak or umbo of a valve.b. In Gastropoda, the first-formed end of a shell.