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Online Dictionary of Invertebrate Zoology: Complete Work - Best Text

Online Dictionary of Invertebrate Zoology: Complete Work - Best Text

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<strong>Online</strong> <strong>Dictionary</strong> <strong>of</strong> <strong>Invertebrate</strong> <strong>Zoology</strong> 815segmental blood vessel (ANN) A blood vessel in the bodywall, connecting anteriorly from dorsal to ventral arteries,and posteriorly by plexes around the gut.segmental spines (ARTHRO: Insecta) In Diptera, 12 majorbristles occurring in transverse rows on each segment <strong>of</strong>syrphid fly larvae.segmentation n. [L. segmentum, piece] 1. The division <strong>of</strong> ajointed appendage or limb. 2. Cleavage.segmentation cavity see blastocoelsegmentation nucleus Nucleus formed by union <strong>of</strong> male andfemale pronuclei during fertilization.segregate n. [L. segregare, to separate] An individual thatdiffers in some genetic characters from the parental stockdue to segregation <strong>of</strong> genes.segregation n. [L. segregare, to separate] 1. The act <strong>of</strong> placingapart; separation. 2. The separation <strong>of</strong> the two genes <strong>of</strong>an allelomorphic pair during meiosis.seizing jaws see grasping spinessejugal a. [L. se, apart; jugare, to join] Indicating the furrowor interval separating divisions or segments <strong>of</strong> an invertebratebody.selection see natural selectionselection pressure The effect <strong>of</strong> the environment in selectingindividuals best suited for survival and reproduction. seenatural selection.selenaster n. [Gr. selene, moon; aster, star] (PORIF) A microscleresimilar to a stellaster, but based on a spiraster.seleniform a. [Gr. selene, moon; L. forma, shape] In theshape <strong>of</strong> a full moon.seleniform cell see plasmatocytesselenizone n. [Gr. selene, moon; zone, girdle] (MOLL: Gastropoda)In dibranchiates, a spiral band <strong>of</strong> crescentric growthlines or threads (lunulae) on the shell surface due to thesemicircular end <strong>of</strong> a notch or slit on the outer lip; a slitband; corresponds to the anal fasciole <strong>of</strong> some othergroups.

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