Dithra see Bivalvia

ditrochous a. [Gr. dis, twice; trochis, runner] (ARTHRO: Insecta) Pertaining to Hymenoptera having a two-segmented trochanter.

diuresis a. [Gr. dia, through; ouron, urine] Pertaining to urine excretion in excess of the usual amount, directly referable to drinking, eating or certain metabolites.

diurnal a. [L. diurnus, of the day] Pertaining to animals active only during the daytime. see nocturnal, crepuscular.

diurnal eyes (ARTHRO: Chelicerata) In spiders, eyes that are dark in color.

diurnal rhythm Having a 24 hour periodic cycle. see cir-cadian.

divaricate a. [L. divaricatus, spread apart] 1. Forked or divided into branches; diverging. 2. (MOLL: Bivalvia) Pertains to ornamentation consisting of widely divergent costulae or other shell ornamentation.

divaricator n. [L. divaricatus, spread apart] 1. A muscle which causes parts to open. 2. (brachio) A muscle from the ventral valve to the cardinal process which opens the shell. 3. (BRYO) One of a pair of muscles which open the mandible for an avicularium or an operculum.

divergent a. [L. diversus, different] Becoming more separated distally; extending in different directions from the same origin.

divergent adaptation Adaptation to different kinds of environmental influence that results in a change from a common ancestral form.

diverse a. [L. diversus, different] Being distinct; differing in size or shape; dissimilar; separate.

diverticulum n.; pl. -ula [L. devertere, to turn away] An outgrowth or pouch of some sort from the main axis of an organ.

divided a. [L. dividere, to separate] Parted or disunited.

divided eyes (ARTHRO: Insecta) 1. One in which the ommatidia in one area are different in size and often in pigmentation. 2. In many Odonata, the dorsal facets are nearly twice the diameter of the ventral ones. 3. In certain Hemiptera, the ventral facets are larger. 4. In some coleopteran water beetles, the eye is divided transversely. 5. In certain Ephemeroptera, the lateral pair are apposition eyes and the dorsal pair are superposition eyes.

dixenic a. [Gr. dis, two; xenos, guest] Rearing of one or more individuals of a single species in association with two known species of organisms. see axenic, monoxenic, polyxenic, synxenic, trixenic, xenic.

dixenous a. [Gr. dis, two; xenos, guest] Parasitizing two host species. see monoxenous.

DNA Deoxyribonucleic acid docoglossate a. [Gr. dokos, main beam; glossa, tongue] (MOLL: Gastropoda) Pertaining to the long radula containing a few strong teeth (up to 12) per transverse row; median radular tooth may be lacking or fused with lateral teeth to form a strong median tooth; marginal and lateral teeth, when present, are uncinate.

dolabriform a. [L. dolabra, ax; forma, shape] Hatchet-shaped.

dolichasters n.pl. [Gr. dolichos, long; aster, star] (ARTHRO: Insecta) In Neuroptera larvae, modified setae on the lateral segmented processes of the dentate mandibles.

dolioform, doliioform a. [L. dolium, wine-cask; forma, shape] Barrel-shaped; globose; capacious.

doliolaria larva (ECHINOD: Crinoidea) A free-swimming bilaterally symmetrical larva of the crinoids and a post auricu-laria holothurian larva; characterized by possessing a large apical tuft and several (4 or 5) ciliated bands around the body; dipluerula. see pentacrinoid.

Dollo's rule The principle that evolution is irreversible, i.e., structures or functions once lost cannot be regained.

dome organ A sensillium campaniformia.

dominant allele An allele that determines the phenotype of a heterozygote. see recessive allele.

dominant character A character from one parent that manifests itself in offspring to the exclusion of a contrasted (recessive) character from the other parent. see recessive character.

dormancy n. [L. dormire, to sleep] A period of inactivity or suspended animation usually referable to adverse environmental conditions, but can be genetically controlled.

dormant a. [L. dormire, to sleep] Being in a state of torpor or sleep, hibernating, quiescent or aestivating.

dorsad adv. [L. dorsum, back; ad, to] Toward the back or top.

dorsal a. [L. dorsum, back] 1. Pertaining to the upper surface or back of the body. 2. (ARTHRO: Crustacea) In Ostracods in normal position, the upper part comprising the area that contains hinge, eyes, antennules, antennae and stomach. 3. (BRACHIO) From the pedicle valve toward the brachial valve. 4. (ECHINOD) see aboral. 5. (MOLL) a. In Bivalvia, the back edge in the region of the hinge. b. In Gastropoda, the back remote from the aperture; the conical top surface of a limpet. 6. (POGON) see adneural.

dorsal area 1. (G.T.) 2. (ARTHRO: Crustacea) In Ostracoda, that part of the valve surface adjacent to the dorsal border, comprised of anterodorsal, mid-dorsal and posterodorsal areas. 2. (MOLL) For chitins, see jugal area.

dorsal arms of the tentorium (ARTHRO: Insecta) A pair of dorsal arms arising from the anterior arms; may be attached to the dorsal wall of the head by short muscles.

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