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Glossary - R





5R and 5L are alternate lineage patterns of the hermaphrodite which are related by twofold rotational symmetry.

VU, Z1.ppa (Ventral Uterine precursor; generates uterus, spermatheca and spermatheca-uterine valve cells)
AC, Z1.ppp (Anchor Cell)
VU, Z4.aaa
(Ventral Uterine precursor; generates uterus, spermatheca and spermatheca-uterine valve cells)
VU, Z4.aap
(Ventral Uterine precursor; generates uterus, spermatheca and spermatheca-uterine valve cells)

See 5L
See Somatic primordium



Evolutionary survival strategy which is typically found in unstable environments where the ability to reproduce quickly is critical for successful survival. r is the growth rate term in the logistic equation (Verhulst model) of population dynamics. Traits that correspond to species that follow an r-selected behavioral strategy usually include: small size, rapid development, high rates of fertility, short generation time and relatively brief life span.

Free-living C. elegans adopts this strategy to make best use of its uncertain environmental conditions. K-selection strategy, by contrast, favors slow development, long life span, and a prolonged period of fertility, with greater parental investment in a few progeny.

See K-selection


A large syncytial compartment of germline cytoplasm which is produced by the fusion of all mitotic and meiotic germ cells at their basal pole to join a common lengthwise tube running centrally through the distal arm of the gonad. The rachis contains no nuclei, but many mitochondria and ribosomes. Each germ cell retains its own nucleus and plasma membranes, so as to remain separate from surrounding germ cells. A thin version of the rachis may extend into the loop, or possibly into the proximal gonad arm. It has also been called the “core” of the gonad (Wolf et al., 1978). The rachis occurs in both the hermaphrodite and male gonad arms, and links germ cells which can go on to become either sperm or oocytes.

Radial muscle  

The form of the pharyngeal muscles, whose myofilament lattice is oriented in radial fashion with respect to the central lumen. Contraction of radial muscles is expected to cause the pharyngeal tissue to thin, dilating the lumen and probably enlarging the outer diameter of the pharynx. Thus the lumen probably closes during muscle relaxation. Most pharyngeal muscles form a two cell syncytium, in which each parent cell contains just one radial sarcomere; therefore these can be included in the single sarcomere class. One pharyngeal muscle, m8, appears to have smooth muscle properties rather than radial properties.

See Single sarcomere muscle
See Smooth muscle
See Striated muscle


See Lipid raft


Specialized bristle-like sensory structure extending into the fan of the male tail, containing two neuronal processes, a structural cell process and a thin hypodermal coat facing the fan cuticle.

A second (archaic) definition of the same word can refer to each of the three thin extensions of the pharyngeal lumen; one ray of the lumen always points to the ventral side of the head, while the others point dorsolaterally.

See Fan
See Genital papilla

Ray cell


The constituents of the sensory rays of the male tail; this attribution generally refers to the two sensory cells, RnA or RnB, but can also refer to the structural cell, Rnst but is rarely to refer to the sister hypodermal cell.

Ray cell group   The cluster of daughter cells from the lineage of any of the tail seam cells, consisting of two neurons, a structural cell and a hypodermal cell, that are needed to form a sensory ray in the male tail. Not every ray cell group successfully forms a normal ray, even in wild type animals; occasional cell groups may spontaneously produce a fused ray with a neighboring cell group or just a small papilla that fails to elongate.
Ray extension     The morphogenetic process by which each ray cell group of the male tail changes in shape from an early papilla to its final finger-like shape within the fan.
Ray precursor cell Rn cell (S)  

Nine pairs of blast cells derived from the three most posterior pairs of seam cells (V5, V6, T) in the male animal that give rise to the ray cell groups by divisions occurring in late L3 and L4 larval stages (Emmons, 2005). These cells then differentiate to produce the nine pairs of sensory rays in the adult male tail, plus a set of hypodermal cells that fuse into the tail's hypodermal syncytium.


This term has multiple uses and can refer to a molecule, to a specialized cell extension such as a cilium, or to a whole cell involved in the transduction of a signal. The signal may represent communication between two cells within the animal, or an external feature in the environment of the animal such as a chemical, pheromone, temperature gradient, etc.

See Neurotransmitter

Reciprocal synapse  

A category of synaptic connection in which the synapse is independently specified in each direction (neuron A connects to neuron B and there is a reverse synapse from B to A). Often reciprocal pairs are adjacent.

See Feedback

Reconstitution of pronuclei

See Pronuclear reformation

Rectal commissure Dorso-rectal commissure (S)

A bilateral pair of minor commissures in the tail between the dorso-rectal ganglion and the preanal ganglion, traveling alongside the left and right sides of the rectum in close apposition to rectal hypodermis and the anal sphincter muscle. These commissures are formed by processes of three neurons; DVA, DVB and DVC. DVA neuron's process travels from the right side whereas those of DVB and DVC travel from the left side.

Rectal cuticle

A specialized cuticle lining the rectal passage which is continuous with the bodywall cuticle in the tail, formed principally by the rectal epithelial cells. The apical specialization of the rectal gland cells also produces cuticle in discrete patches (Hall, unpublished data).

Rectal epithelium


These cells include: B, F, Y, U, K' and K. All rectal epithelial cells contain secretory membrane stacks along this region facing the lumenal cuticle and produce some portion of the cuticular lining of the rectum. These are interfacial cells that connect the alimentary system to the main body syncytium, analogous to the function of the arcade cells of the lips.

Rectal gland

A set of three large cells (rectD, rectVL and rectVR) that lie next to the intestine and connect to the intestinal lumen just posterior to the rectal valve. These cells form both microvilli and some cuticle along the posterior border of the intestinal lumen and the near portion of the rectal lumen and are presumed to secrete materials into these lumenal spaces, perhaps to aid digestion and/or molting, or as a source of pheromones to signal neighboring animals.

See Caudal glands

Rectal muscle

Anal sphincter (S)
Anal dilator (S)
Anal depressor (S)


This term can refer to either of the two enteric muscles, the sphincter (also known as the dialator) or the depressor, which reside in the posterior region and function in the defecation cycle. The sphincter muscle is thought to open and close the rectal valve while the depressor muscle acts to open the rectal passageway.

Rectal opening Anus (S)  

The caudal opening of the rectum in the tail of the hermaphrodite. In mature males this is called the cloacal opening. The opening is covered by specialized hypodermal cells whose apical surfaces are bound by cuticle and whose basal surfaces are covered by the basal lamina.

Rectal valve Intestinal-rectal valve (S)   Two small epithelial cells (virL and virR) form the valve by blocking the lumen of the posterior intestine. Narrow channels perforate the occlusion to allow digested material to leak into the rectum and then the anus. It is not clear that this functions as a true valve as the cells do not appear to have any contractile elements.
Rectum Proctodeum (S)

A cuticle-lined sinus opening on the posterior ventral surface of the animal, from which the alimentary system excretes waste products. It lies just behind the rectal valve and may receive secretions from the rectal gland cells. It is formed by a tube of large rectal epithelial cells, some of which can also act as blast cells for late larval cell divisions. The rectum may be opened by contractions of the anal sphincter muscle, which is firmly secured to the roof of the rectal cuticle. In males, the rectum (called the proctodeum) provides an outflow for the genital tract as well as the alimentary tract. It also houses the copulatory structures.

See Proctodeum



Typically this refers to the recycling of receptors to the plasma membrane as a step in the endocytic pathway. This usually occurs via recycling endosomes.

See Endocytosis
Recycling endosome    

An endosome that recycles receptors to the plasma membrane.

Reflexed/ Reflexion


Bending of an organ to become doubled back upon itself; generally used with respect to describe the “reflexed” gonad arm, a very long tubular organ which stretches out lengthwise within the body cavity and reverses (reflexes) once to extend for an additional distance next to itself. The amphidelphic gonad of C. elegans produces two equivalent “proximal” arms projecting away from the vulva, and each arm reflexes once (near the head or tail) before projecting a “distal arm” in the opposite direction and terminating again in the region of the vulva.

Refractile/ Refractility


A property (of a cell or cell part) of being highly visible by light microscopy due to the noticeable refraction of light compared to the surrounding area, whether under normal illumination, or under specialized optics such as DIC or polarized light. In C. elegans structures such as the intestine or apoptotic cells are particularly noticeable due to their refractile properties.

See DIC microscopy



Unresponsive to a given signal or stimulus.

Regulation/ Regulative potential  

The ability of the cells within the organism to detect changes in cell fates of neighboring cells and to reprogram their own cell fates to adopt a fate that best suits the needs of the entire organism. Such regulatory re-programming is common in higher animals, but rather uncommon in nematode cell lineages. In C. elegans, the fates of most adult cells are strictly ruled by internal programming decisions governed by their specific cell lineage, and not by signaling from neighboring cells (Sulston and Horvitz, 1977). Limited examples of regulation have been detected in the later differentiation of somatic gonad structures and other secondary sexual features (Sulston and White, 1980; Sternberg and Horvitz, 1984).

Reiterated cell lineages  

A repeated pattern of cell lineage produced by the patterned expression of specific genes.

See Reiterative

Reiterative Reiterated neurons (S)

A lineage pattern in which certain progeny cells repeat a pattern of cell divisions previously displayed by either the parent cell or the grandparent cell  (Sulston and Horvitz, 1981; Chalfie et al., 1981). Some mutants, such as lin-4 and unc-86, can cause defects in the control of reiterative lineages, leading to either the loss of certain postembryonic structures, or to gross proliferations and the creation of many extra (small) cells in place of normal blast cells, or to the creation of supernumerary structures.

See Proliferative

Rennette cell


A modified form of excretory cell found in some nematode species that may replace the functions of the excretory canal and gland cells (Narang, 1972).

Repellant/ Repulsion


A moiety that causes an animal (cell, tissue or cell part) to move away from that moiety.
Repulsion of C. elegans individuals can be elicited by various environmental stimuli, including acid pH (H+), D-tryptophan and high osmolarity (Dusenbery, 1975; Culotti and Russell, 1978). Repulsive guidance of a migrating cell process will stimulate the process to grow away from the source of the repellant (Wadsworth et al., 1996).

See Attractant

Reproductive tract Genital tract (S)

The portion of the body that is devoted to production, storage and fertilization of germ cells and the incubation of fertilized eggs. In the adult hermaphrodite this term would encompass the distal gonad arms, the proximal gonad, spermatheca, uterus and vulva. In the adult male, it would refer to the gonad, vas deferens and cloaca.

RER Rough endoplasmic reticulum See Endoplasmic reticulum

Residual body


A cytoplast which forms in the germline during the late stage of meiotic cell division of a spermatocyte. Initially it is connected to several secondary spermatocytes and receives some cytoplasmic elements by transfer across the syncytial bridge, but these products are discarded into the cytoplast as the individual spermatocytes mature to become spermatids.




Analogous to the metamorphic changes in some higher animals, C. elegans can resorb some structures when reshaping its body, particularly in dauer formation and in male tail formation. To become thinner and less voluminous, the predauer larva resorbs some epithelial tissues (esp seam cell) via autophagy (Melendez et al., 2003). During male tail morphogenesis, the larval tail spike is resorbed during a phase called retraction, during which many cells crawl anteriorly.

See Retraction






The physiological rate of oxygen consumption per individual. C. elegans and C. briggsae are not adapted to anaerobic conditions and require oxygen to develop and thrive. However, they can temporarily survive in complete anoxic conditions by entering a quiescent (cryptobiotic) state (Nicholas, 1975; Padilla et al., 2002).




Has several meanings, including a special meaning as step in male mating behavior called "response to contact" (Liu and Sternberg, 1995; Peden and Barr, 2005) .

See Male mating behavior

Reticular membrane


A conformation of the rough endoplasmic reticulum in which it dilates somewhat to form a series of inflated balloon-like spaces that can show as alternating light and dark stripes within the cell body, either by light microscopy (in muscle, see Rolls et al., 2002) or by TEM (in some ray neuron cells, see Sulston et al., 1980).


This term has several uses in C. elegans:

1) A feature in male tail development where the shape of the male tail is created by the retraction of surrounding tissues which leads to the formation of the fan and the rays. The retraction is a property of the hypodermal cells of the tail (Emmons, 2006).

2) A feature in axon remodeling or growth cone guidance.

3) A feature of sperm movement which occurs by extension of the leading edge of the pseudopod, followed by attachment to the substrate and then retraction of the cell body.

See Fan formation
See Resorption

Retractor cell  

SM2R.paa SM1R.ppp
SM2R.apa SM2L.apa

Dorsal right spicule retractor
Ventral right spicule retractor
Dorsal left spicule retractor
Ventral left spicule retractor
Right gubernacular retractor
Left gubernacular retractor

See Retractor muscle

Retractor muscle

retr (abbrev)




Male specific muscles that come from two groups: the spicule retractors (dsrL/R and vsrL/R) and the gubernacular retractors (grtL/R). The spicule retractor muscles attach to the base of each spicule and the sublateral body wall where contraction of these muscles pulls the spicules up inside the body of the animal. The gubernacular retractor muscles attach at their ventral edges to the gubernaculum and overlying proctodeal epithelium while their dorsal edges attach to the sublateral dorsal body wall and control the positioning of the gubernaculum during copulation.

See Retractor cell
See Spicule
See Gubernaculum

Retrovesicular ganglion RVG

The retrovesicular ganglion lies at the anterior limit of the ventral nerve cord, near the ventral ganglion and nerve ring in the head posterior to the excretory pore. It is open and continuous with the region containing the motoneurons of the ventral cord. In the early L1 this ganglion holds 12 neuron cell bodies plus one neuroblast (Sulston and Horvitz, 1977; White et al., 1986). In the adult animal, the ganglion holds 20 neuron cell bodies.


A characteristic behavior of normal animals after sensory input to the head (touch, heat, aversive stimuli), in which the animal stops forward motion and immediately begins to move backwards for one or more body lengths, after which the animal usually resumes forward motion (Croll, 1975). The are other distinctive types of reversals, including the omega turn, and in the male mating behavior, a deep ventral bend beginning near its tail while moving backwards.

See Deep ventral bend
See Male mating behavior
See Omega turn
See Pirouette




A group of nematode species that includes a large number of ecologically and genetically diverse species, including C. elegans. It is a subset of the Phasmidia (Secernentea), categorized on the basis of their mouthparts, which have given rise to many parasitic species, including many plant parasites, as well as many free-living soil nematodes (Kiontke and Fitch, 2005; Sommer, 2005).

Rhabdion/ Rhabdia    

Specialized types of cuticle lining individual zones within the buccal passage; thus the cheilostom is lined by the cheilorhabdion, the prostom lined by the prorhabdion, etc. (Bird and Bird, 1991, after Goodey, 1963; Van de Velde and Coomans, 1991).

See Cheilorhabdion
See Mesorhabdion
See Metarhabdion
See Prorhabdion
See Telorhabdion



Birefringent crystals which collect in the gut 4-6 hours after the first cleavage and are an early marker for gut differentiation and are thought to be products of tryptophan catabolism (Goldstein, 1993).

See Gut granule


Large macromolecular complexes that function to translate mRNAs into protein. Free ribosomes lie within the cytoplasm in loose clusters, whereas other ribosomes are firmly attached on rough endoplasmic reticulum.  These two classes of ribosomes generally produce protein for different destinations. Free ribosomes generally produce soluble proteins meant to lie within the cytoplasm, whereas RER ribosomes produce proteins that are first sequestered inside the RER, or in the RER membrane, prior to export from the cell or packaging in a cell membrane or an organelle lumen.

Rich media



A culture medium that contains nutrients in excess of the minimum necessary to sustain life, normal development and reproduction. Such additional additives might be included to promote faster growth, longer life, or healthier activity.

See Defined medium

Right roller

Right-hand roller (S)


Rolling movement is caused by disruption of the normal function of collagen genes that form the cuticle such that the animals roll around a right handed helix pattern.

Ring and dot


A staining pattern observed by light microscopy at the tips of the rays in the developing male tail, apparently caused by the robust adherens junctions which secure the distal structural process to the hyp and/or cuticle (the ring) and the distal end of the RnB cilium to the cuticle opening (the dot). Ray 6 does not show this pattern since it is the only one not open at its tip. The feature was originally noted by DIC optics, but is also congruent with the pattern of MH27 [JAM-1] staining, and with serial thin section data.

Ring cell  

Vulval epithelial cells (A, B1, B2, C, D, E, F) undergo morphological changes generating a seven stacked ring formation. Specific cells migrate towards the center forming half toroid. These half toroids fuse together in a stereotyped sequence for form the vulval rings (Shemer et al., 2000).

See Vulva

Rn cells    

Nine bilateral pairs of rays (numbered n, 1-9). Each ray consists of the endings of two sensory neurons (RnA and RnB) surrounded by a ray structural cell (Rnst).

See Ray cell group

RNAi RNA-mediated interference  

This refers both to a common technique with which one can produce “mutant” phenotypes in wild type animals (Fire et al., 1998), and to the normal developmental process by which an animal cell can protect itself against invading viruses (Schott et al., 2005; Wilkins et al., 2005) and transposable elements (Sijen and Plasterk, 2003). In worms, individual cells can use this process to detect invading (foreign) dsRNAs and to destroy them. As a laboratory method, the RNAi response is utilized to trick cells into blocking the normal expression and function of the gene of choice.

See Immune response

Roaming behavior Dwelling (A)

A behavioral state in which the nematode tends to move forward actively at relatively high speed, with a reduced rate of turning (Bargmann, 2006). This behavior is equivalent to the “rover” behavior in Drosophila (Cheung et al., 2005). Some wild strains, including the Bristol lab strain, use this strategy when they find food to disperse themselves from their neighbors to forage alone (de Bono and Bargmann, 1998).

Rod-like lethality



A common phenotype in certain types of mutants (for instance in the Ras pathway) in which the animals adopt a rigid shrunken appearance at the late L1 stage before dying. This is visibly different from “scrawny” L1s in some other lethal phenotypes in which the dying animal is also quite thin but much more mobile.

Roller Rol  

A genetic mutation affecting the cuticle structure that causes a helical twist in the shape of the body, forcing the animal to move in a characteristic rolling or circular motion, dominated by the shape and handedness of the helical twist (it can be either left- or right-handed in nature). As the animal slowly progresses forward, it tends to rotate around its long axis, and over time the animal may be confined to a small circle on the bacterial lawn.

See Left roller
See Right roller
See Fiber layers
See Locomotion
See Squat phenotype


See Striated rootlet


A  briefly observed structure which appears by DIC optics. About 10 minutes before cell division, just prior to dissolution of the nuclear membrane and the formation of the metaphase plate, the nucleoplasm surrounding the nucleolus becomes coarsely granular and can produce a rosette pattern around the nucleolus (Sulston and Horvitz, 1977).


1) Can refer to a specific step during prophase of the one cell embryo, when the centrosomes and pronuclei rotate 90° in synchrony to a new orientation at the exact center of the embryo (Oegema and Hyman, 2006).

2) Can also refer to the early two cell stage, after the centrosomes migrate onto a transverse plane, the P1 nucleus rotates 90°to align the centrosomes on the AP axis (Gönczy and Rose, 2005).

See Centration

Rough endoplasmic reticulum

Rough ER

A subset of the endoplasmic reticulum that is studded with ribosomes (giving it the rough appearance) and is generally in continuity with the nuclear envelope. In neurons, most RER lie in the cell body, but some may also extend into cell processes and even this distant domain remains in continuity with that in the cell body (Rolls et al., 2002).

Rubberband phenotype  

A characteristic body-shortening behavior seen in some mutations affecting neuromuscular signaling where the entire body undergoes coordinate contraction of all bodywall muscles in synchrony to shorten the animal, and then coordinate relaxation to restore the animal to full length (Levin and Horvitz, 1992; de la Cruz et al., 2003).

See Convulsion


A period of forward motion that is not interrupted by a reversal. Different behavioral states tend to produce either short runs, or mostly long runs (Pierce-Shimomura et al., 1999; Lockery in Hart, 2006)

Edited for the web by Laura A. Herndon. Last revision: September 20, 2011. This section should be cited as: Herndon, L.A. and Hall, D.H. 2010. Glossary R. In WormAtlas.  doi:10.3908/wormatlas.6.18