Radii see rays

radiobiology n. [L. radius, ray; Gr. bios, life; logos, discourse] The study of the effects of radioactivity on living organisms.

radiocarbon n. [L. radius, ray; carbo, coal] A radioactive isotope of carbon found naturally in the air and in organisms that is used to date fossil and subfossil remains; also used in physiological studies.

radioecology n. [L. radius, ray; Gr. oikos, house; logos, discourse] Radiation ecology; study of effect and trophic pathways of radioisotopes in communities.

radioisotopes n.pl. [L. radius, ray; Gr. isos, equal; topos, place] Unstable forms of elements that show radioactivity.

radiole n. [L. dim. radius, ray] 1. (ANN: Polychaeta) Featherlike head structures forming a crown, or modified into a long stalked knob (operculum); functioning in filtering particles for food. 2. (echinod: Echinoidea) The spine of sea urchins.

radiomimetic a. [L. radius, ray; Gr. mimos, mime] Chemical agents causing effects similar to ionizing radiation in living systems.

radioresistant a. [L. radius, ray; re-, back; stare, to stand] Organisms or tissues resistant to damage by radiation.

radiosensitive a. [L. radius, ray; sentire, to feel] Sensitive to radiation effects.

radius n.; pl. radii [L. radius, ray] 1. In radially symmetrical animals, the primary axis of symmetry. 2. (ECHINOD: Cri-noidea) One of 5 reference planes passing through the polar or central axis and median line. 3. (ARTHRO) a. In Crustacea (sessile barnacles), the lateral part of a com-partmental plate when marked off from the median triangular area by change in direction of growth lines. b. In In-secta, the third longitudinal wing vein.

radix n. [L. radix, root] 1. A primary source. 2. (ARTHRO: Cheli-cerata) In Arachnida, apophysis of male copulatory organ. 3. (ECHINOD: Crinoidea) The rootlike distal anchorage of the stem; holdfast.

radula n.; pl. radulae [L. radula, scrape] 1. (ARTHRO: Insecta) The raster. 2. (MOLL) A uniquely molluscan feeding rasplike organ, odontophore or lingual ribbon, armed with chitinous denticles, found in nearly all mollusks, except clams.

radula sac (MOLL) An evaginated pocket in the posterior wall of the buccal cavity containing on it's floor the radula. see raster.

radulifer n. [L. radula, scrape; fero, to bear] (BRACHIO) A hook-shaped or rodlike crura on the ventral side of the hinge plate, projecting toward the pedicle valve.

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