cristulate a. [L. dim. crista, crest] Having a small crescent-like ridge or crest.
critical group A taxonomic group of organisms that cannot be subdivided into smaller groups.
croceous a. [Gr. krokotos, saffron-yellow] Of the saffron-yellow color.
crochet, crotchet n. [F. crochet, small hook] 1. (ARTHRO: In-
secta) In Lepidoptera and on other insect larvae, one of a series of sclerotized hooklike cuticular structures, in rows or circles on the prolegs; also on cremaster of chrysalides; frequently called hooks. 2. (ANN) see crotchet.
crook n. [ON. krokr, crook] A hook; recurved tip; bend or curve.
crop n. [A.S. crop, craw] An enlarged portion in the alimentary canal in certain invertebrates functioning in storage or transporting and passing on to the digestive tract; the ingluvies; esophageal bulb.
crop caeca (ANN: Hirudinoidea) Segmental pouches or diverticula of the crop.
cross n. [OF. crois, cross] An organism produced by two differing forms; hybrid.
crossed-lamellar shell (MOLL: Bivalvia) A shell structure with secondary lamellae inclined in alternate directions within the primary lamellae.
cross-fertilization The union of gametes from different individuals; allogamy; allomixis; xenogamy. see self-fertilization.
crossing over The exchange of corresponding portions of homologous chromosomes during synapsis.
cross-reflex The reaction of an effector on one side of the body to stimulation of a receptor on the opposite side.
cross section A cut of an organism or structure at right angles to the longitudinal axis; a transverse cut.
cross-striation In striped and cardiac muscle fibers, dark bands running across a fiber perpendicular to the myofibrils and representing lines of A-bands.
cross veins Any vein connecting adjacent longitudinal veins.
crotchet n. [F. crochet, small hook] 1. A hooked or forklike process. 2. (ANN) A curved seta (chaeta), notched at the distal ends. 3. (ARTHRO: Insecta) see crochet.
crown n. [L. corona, crown] 1. A circular structure at or near the summit of an organ or part. 2. A corona. 3. (ECHINOD: Crinoidea) The whole crinoid without stem; corona. 4. (nemata) see corona radiata.
cruciate a. [L. crux, cross] Crossing; shaped like a cross.
cruciform a. [L. crux, cross; forma, shape] Resembling a cross; cross-shaped.
cruciform muscles (MOLL: Bivalvia) Two bundles of muscle fibers joining valves and intersecting to form a cross.
crumena n. [L. crumena, purse] (ARTHRO: Insecta) An internal pouch in the head for retraction of mandibular and maxillary bristles.
crura n.pl.; sing. crus [L. crus, leg] 1. Any leg-like part. 2. (BRACHIO) A pair of prongs (brachidium) extending from the cardinalia or septum to support the lophophore. 3. (MOLL) A stalk or peduncle. 4. (NEMATA) Lateral extensions of the cuneus of the gubernaculum. 5. (PLATY: Turbellaria) Branches of the intestine of a flatworm. crural a.
crura cerebri (ARTHRO: Insecta) The two large nerve cords connecting the supra- and subesophageal ganglia.
cruralium n. [L. crus, leg] (BRACHIO) A U-shaped ridge of the brachial valve that bears adductor muscles.
crural plates (BRACHIO) Vertical plates that attach the crura to the dorsal valve.
crural process (BRACHIO) The pointed portion of the crus, directed obliquely inwardly and ventrally.
crus sing. of crura
Crustacea, crustaceans n.; n.pl. [L. crusta, shell] One of the divisions of arthropods, having chitin-encased bodies that may or may not be impregnated with calcium salts; contains the shrimp, crabs, lobsters, barnacles, water fleas, sand hoppers, fish lice, wood lice, sow bugs, pill bugs, scuds and slaters. crustaceous a.
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