Rhizocaul rhizocaulome see hydrocaulus

rhizoclad n. [Gr. rhiza, root; klados, branch] (PORIF) A megas-clere desma with rootlike processes; rhizoclone rhizoid n. [Gr. rhiza, root; eidos, like] (BRYO) A rootlike structure composed of one or more kenozooids.

rhizoid spines (BRACHIO) Spines that serve to attach the animal, either by entanglement or by cementing themselves to a foreign surface.

rhizome n. [Gr. rhiza, root] (CNID: Hydrozoa) The stolon; the hydrorhiza.

rhizomorphous a. [Gr. rhiza, root; morphos, form] Root-like.

rhizophagous a. [Gr. rhiza, root; phagein, to eat] Root-eating.

rhodopsin n. [Gr. rhodon, rose; ops, eye] (ARTHRO: Insecta) A visual pigment of the rhabdomeric microvilli, on which the primary photoreceptor process depends.

rhombogen n. [Gr. rhombos, revolve; gennaein, to produce] (MESO: Rhombozoa) A stage in the life cycle in the adult in a sexually mature host; stage follows the nematogen phase and produces infusorigens.

Rhombozoa, rhombozoans n.; n.pl. [Gr. rhombos, revolve; zoon, animal] A class of Mesozoa; minute parasitic animals in the renal organs of Cephalopoda.

rhombus n. [Gr. rhombos, revolve] A parallelogram with oblique angles. rhomboidal a.

rhopalium n.; pl. -lia [Gr. rhopalon, club] (CNID) A hollow tentacle or sense organ with endodermal statoliths and rarely ocelli, that lay in each notch between the lappets at the end of a pedalium; lithostyle; statorhabd; tentaculo-cyst; statocyst; colletocystophore.

rhopalocercous cercaria (PLATY: Trematoda) Cercaria possessing a tail as wide as, or wider than, the body.

rhopaloneme n. [Gr. rhopalon, club; nema, thread] (CNID: Anthozoa) A nematocyst with the tube consisting of an elongate sac and a club-shaped thread with an adhesive nature.

rhopalostyle n. [Gr. rhopalon, club; stylos, pillar] (PORIF) A lumpy megasclere spicule with a bifurcate head.

rhynchocoel n. [Gr. rhynchos, snout; koilos, hollow] (NEMER) A dorsal fluid-filled tubular chamber that houses the ever-sible muscular proboscis.

Rhynchocoela n. [Gr. rhynchos, snout; koilos, hollow] Formerly used in place of Nemertea.

rhynchocoel villus (NEMER) A blood vessel running in the mid-ventral line of the rhynchocoel.

rhynchodaeum n. [Gr. rhynchos, snout; demas, body] 1.

(ANN: Hirudinoidea) A cavity at the anterior end of the digestive tract. 2. (NEMER) A tubular chamber anterior to the proboscis, opening anteriorly by means of the proboscis pore.

rhynchostome n. [Gr. rhynchos, snout; stoma, mouth] (NEMER) The proboscis pore.

rhynchoteuthis stage (MOLL: Cephalopoda) In Ommastrephi-dae, a juvenile form with tentacles fused into a rostrum or trunklike proboscis; the tentacles separate later.

rhypophagous a. [Gr. rhypos, dirt; phagein, to eat] Eating dirt or filth.

rhythm n. [Gr. rhythmos, measured motion] Regular periodic changes. see circadian, diurnal.

rib n. [A.S. ribb, a rib] 1. In Gastropoda and Brachiopoda shells, a long and narrow ridge; a costa. 2. (MOLL: Bivalvia) A broad and prominent elevation of the shell surface; usually directed radially; costa.

Ribaga's organ (ARTHRO: Insecta) In some female Hemiptera, pouches on various places of the nongenital abdomen; hemocoelic fecundation instead of by means of the customary ducts; ectospermalege; Berlese's organ. see mesospermalege.

ribbon n. [OF. ribon] (MOLL: Gastropoda) A flat spiral surface elevation.

riblet n. [A.S. dim. ribb, rib] A small or rudimentary rib; costella.

riboflavin n. [L. alteration of arabinose; flavus, yellow] 6,7-dimethyl-9-D-ribitylisoallozazine, a water-soluble yellow pigment, generally occurring in animal tissues in a form in which it is metabolically active.

ribonucleic acid (RNA) Long chain polymers of ribose and certain organic bases; differing from DNA in using the base uracil and usually single stranded.

ribose n. [L. alteration of arabinose] Pentose sugar which with certain organic bases makes up RNA and DNA polymers.

ribosome n. [L. alteration of arabinose; Gr. soma, body] Aggregations of RNA and proteins that act in synthesis of proteins.

ridge n. [A.S. hrycg] Any raised line or strip on a surface.

right valve (MOLL: Bivalvia) When holding the bivalve shell with the hinge up and the apex or umbo pointed away from and pallial sinus toward the holder, then the right valve is on the right.

rimate a. [L. rima, fissure] 1. Provided with a very narrow cavity; a very small hole or crack. 2. (MOLL: Gastropoda) Referring usually to the umbilicus.

rimose a. [L. rima, fissure] Having many clefts or excavations.

rind cells The layer of nerve cell bodies on the surface of invertebrate ganglia, consisting of perikaryon, glial and neuron cells; not nerve endings or synapses.

ring n. [A.S. hring, ring] 1. A circle or annulus; circinate. 2. (ARTHRO: Diplopoda) A non-systematic and colloquial term for the trunk segments; avoids the need to differentiate between single segments and diplosegments.

ring canal 1. (CNID: Hydrozoa) A circular canal around the margin of the umbrella into which the radial canal join as part of the gastrovascular system. 2. (ECHINOD) A circular part of the water-vascular system encircling the esophagus ringed gland (ARTHRO: Insecta) In Hemiptera, a gland, sometimes paired, situated dorsally or ventrally on the vagina, or on the vaginal pouch; sometimes ringed by annual sclerotizations known as ring sclerites.

ringent a. [L. ringens, gaping] (MOLL: Bivalvia) Gaping, as some valves.

Ringer's solution Used as a physiological saline for vertebrates and invertebrates.

ring gland 1. (ARTHRO: Insecta) In higher Diptera, a glandular organ surrounding the aorta just above the brain, formed by the combining of the corpora cardiaca and the corpora allata and the thoracic glands; Weismann's ring. 2. (PLATY: Trematoda) A ring of glands opening with the aperture above to secrete a substance to digest the epidermal cells of the host.

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