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Glossary - A




A band  

The bundle of thick (myosin) and thin (actin) filaments running lengthwise within the sarcomere of bodywall muscles, best viewed by polarized light, or by phalloidin or antibody staining. Runs in parallel with I bands to form a series of alternating bright and dark bands (Waterston, 1988; Miller et al., 1983). The A band is brighter by polarized light, with a thin darker central stripe, the H zone; the A band contains interdigitating thick and thin filaments.

See H zone
See I band
See M line

A fiber A subfiber (S) A specialized microtubule within the ciliary axoneme (Chalfie and Thomson, 1982; Perkins et al., 1986).
A motor neurons  

Class A motor neurons are a subset of the ventral cord motor neurons which drive the bodywall muscles and execute backward movement. This class of neuron includes VA and DA cells.

See DA neurons
See VA neurons

"a" neuron


AWA cell (S)

Amphid wing "a" cells, neurons having ciliated sheet-like sensory endings closely associated with amphid sheath.
AB blastomere AB P0a

An early blast cell (embryonic founder cell) in the developing embryo which gives rise to many ectodermal cells, principally hypodermis, neurons and accessory cells. The daughters of the cell divisions of such a blast cell are named according to the orientation of the subsequent cell division planes, for instance: ABa and ABp are the anterior and posterior daughters of AB.
In early studies of other nematode species this blast cell was also called the S1, or “somatic” blastomere.

Ablation   The physical removal of a cell, organelle or tissue (for instance by surgery, laser or genetic means).

Anterior body contraction. A motor step in defecation behavior in which anterior body wall muscles contract to concentrate the intestinal contents before the posterior body wall muscles contract.

See Defecation motor program
See pBoc

AC   See Anchor cell
AC/VU decision   A cell fate choice which occurs in the somatic germline between two cells (Z1.ppp and Z4.aaa) with equal chances to adopt the AC fate. After one cell adopts the AC fate, signaling between these cells then causes the remaining cell to adopt the VU fate (Greenwald, 1997).
Accessory cell(s)   A subset of interfacial cell group. It can refer to socket cells, sheath cells and structural cells or their processes. All of these cells extend long processes which serve a supporting role, rather like glia, by forming a protective environment around sensory neuron endings. In addition, some of these cells extend broad thin processes from their somata which wrap around neuropil, similarly in a glia-like fashion.
Accessory structures   This term has been used with regard to the muscle sarcomere to encompass those proteins and physical elements which attach the visible myofilament lattice to the cell membrane and bodywall. These structures include the dense body, the M-line, intermediate filaments inside the muscle cell, perhaps hemidesmosomes or even basal lamina components on the outside of the cell (Waterston, 1988).
Acentriolar   Refers to a condition of the meiotic spindle apparatus during oogenesis in which the condensing chromosomes begin to line up, surrounded by diffuse, unaligned microtubules to form a barrel-shaped structure (when viewed by light microscopy) which lacks organizing centrioles (Albertson et al., 1997). During spermatogenesis, the meiotic spindle apparatus is organized differently than in oogenesis, and always involves centrioles.
Achiasmate chromosomes Noncrossover chromosomes (S)

Condensed chromosomes that lack visible points of crossover (attachment) during meiosis, a condition that is increased in some mutants which interfere with crossovers.

Actin Thin filament (S)

An abundant cytoskeletal protein in most cells, often linked to the plasma membrane and concentrated at cell junctions. Can assemble in different forms to create a mesh-like web or gel (g actin) underneath the plasma membrane, or long parallel fibers (f actin; as in muscle sarcomeres or stress fibers) stretching between distant portions of the cell. Through interactions with myosin motors and with anchoring proteins on organelles and the plasma membrane, these thin filaments help to provide the basis for cell shape changes, tissue rigidity, morphogenetic movements, and muscle contraction.

See Myosin
See Thin filament

Active zone Release zone (S)
(Pre)synaptic bar (S)
Presynaptic density (S)
Presynaptic darkening (S)
The portion of a neuron’s pre-synaptic membrane that is specialized for the directed release of synaptic vesicles into the synaptic cleft. It is recognized morphologically as an electron dense thickening or tuft lying on the cytoplasmic side of the plasma membrane, at which several small round vesicles may be “docked”, ready for release. There is generally no visible post-synaptic specialization seen in thin sections in C. elegans synapses.
Actomyosin   The combined macromolecular structure of actin + myosin; these two filamentous structures slide past each other in muscles to produce muscle contraction (the powerstroke) or relaxation (by sliding in the opposite direction).
Ring interneurons
Adaptation   This term has several very different definitions, depending upon the context:
Evolution: The general ability of a species to undergo (evolutionary) change in order to accommodate changing environmental conditions.
Genetics / Development: A specific change in structure, developmental pattern, or behavior that results from a genetic alteration in response to changing environmental conditions and improves the animal’s chance of survival.
Behavior: Any change in behavior that is prompted by changing environmental conditions.
Neurological / Sensory: A reduction in neuronal sensitivity (reduction in firing rate or size of evoked potentials) to repeated stimuli of constant intensity. Sensory adaptation is likely to play a role in some normal mechanisms of body movement in C. elegans (Dusenbery, 1980) and has been shown to change responses to volatile odorants (Bettinger and McIntire, 2004).
Anterior deirids, sensory receptors in lateral alae, contain dopamine.
ADE sheath cell ADEshL

Anterior deirid sheath cells.

See Anterior and Posterior Deirid Sensilla

ADE socket cell ADEsoL

H2 aaL
H2 aaR

Anterior deirid socket cells.

See Anterior and Posterior Deirid Sensilla

Adenophora   See Aphasmidia
Amphid chemosensory neurons, dual ciliated sensory endings, enter ring via commissure from ventral ganglion, take up FITC.
Adherens junction


Belt junction (S)
Belt desmosome (S)
Zonula adherens (S)

The most common form of intercellular junction between epithelial cells in C. elegans. At high resolution these junctions display many cell specific differences in size and cell-cell spacing. This suggests that some tissues utilize AJ's in order to provide cell-cell adherence at their apical borders, while other AJ's also create a severe restriction or sealing of the extracellular space (tight junction-like) between cells. This is seen in tissues which undergo stronger forces and tend to form larger, more robust adherens junctions.

In most instances, these junctions form belt desmosomes, also known as zonula adherens, stretching along a continuous narrow border near the apical side of epithelial cells to link two neighboring cells tightly together. Spot desmosomes, also called macula adherens, are rare in C. elegans, though they have been seen in somatic sheath (Hall et al., 1999; Hall, unpublished).

Very similar structures, hemi-adherens junctions or hemidesmosomes, form as one-sided membrane appositions in epithelial cells to the cuticle.

See Hemidesmosome
See Ring and dot
See Sealing junction
See Secretory membrane
See Self-junction
See Tight junction

Aerotaxis Aerokinetic response (S) The guided behavior of an animal to approach or avoid a source of oxygen. In C. elegans, “body cavity” receptors sense oxygen levels and the animal can choose between “social behavior” and solitary feeding depending on several factors including oxygen tension in the environment (Gray et al., 2004; Cheung et al., 2005). C. elegans prefers oxygen levels between 2-12%, and can navigate via aerotaxis to find such an environment, avoiding both hypoxia and hyperoxia.
Amphid chemosensory neurons, dual ciliated sensory endings, project directly to ring, take up FITC.
Adhesion plaque Focal Adhesion (S) A specialization of the plasma membrane, occurring in early cell development, which can act to anchor cytoskeletal elements to the membrane in preparation for a cell shape change or the provisional binding between two adjacent cells prior to formation of a full-fledged intercellular junction. This term is used in describing the anchorage of the developing sarcomere apparatus in muscle assembly, prior to development of the dense body structure.
AFD cell


Finger cell (S)

Amphid finger cells, associated with amphid sheath. AFD dendrites terminate anteriorly in small fingers, or villi, that project from the basal body into a series of narrow extracellular channels within the amphid sheath cell. The fingers are believed to be involved in temperature transduction for thermosensory behaviors (Perkins et al., 1986; Cassata et al., 2000).
Age pigments   Endogenous fluorescent compounds that accumulate with increasing age. These compounds include lipofuscin, a heterogeneous mix of oxidized and cross-linked molecules, such as proteins, lipids and carbohydrates that accumulated in lysosomes (Yin, 1996), and advanced glycation end-products. Studies using in vivo spectrofluorimetry have correlated the accumulation of age pigments in C. elegans to the physiological age (rather than chronological age) of the animal and suggest that age pigments can be used as a biomarker for nematode healthspan (Gerstbrein et al., 2005).
AGE products Advanced glycation end-products

Age-related fluorophores formed by non-enzymatic sugar addition to free amino groups of proteins followed by autocatalyzed cross-linking (Ulrich and Cerami, 2001).

See Age pigments

Aggregation Dispersal (A)

A social behavior in which nematodes choose to move together into a tight grouping, often to feed (De Bono et al., 2002), or perhaps as a preliminary step in sexual behavior. This is the opposite behavior from dispersal, and generally only occurs in the presence of food.

See Bordering
See Dispersal
See Pheromone
See Social feeding

Agonist Antagonist (A) Chemical compound producing a ligand-like effect when binding to a receptor.
Amphid interneurons
Amphid interneurons
Ring interneurons
Ring interneurons
Amphid interneurons
Amphid interneurons

Ala/e (/pl)



Small linear ridges running along the lateral lines of the cuticle, lengthwise along the body; these thickenings lie in register with the seam cells which likely produce them and are present in the cuticle of the L1, dauer and adult stages, but not in other larval stages. The alae are suspected to provide better traction when the animal generates a bodywave. Since the animal usually lies on its side, the alae are in perfect position to catch against the substrate.

ALA cell ALA ABalapppaaa Neuron, sends processes laterally adjacent to excretory canal and also along dorsal cord.
Alar   Referring to the ala/e.
Alimentary tract

Digestive tract (S)
Gastrointestinal system (S)

A series of related tissues lying within the body cavity and devoted to feeding and digestion; they form a continuous single tube that includes the pharynx, intestine, rectum and anus and related valves, glands and muscles.

A chemical that affects the growth, health or behavior of a different species. Chemicals that mediate interactions within a species are called pheromones.

See Allomone
See Pheromone


A type of allelochemical that is produced and released by one individual that affects the behavior of another (Huettel, 1986). Usually this is used as a defensive mechanism by plants against insects.

See Allelochemical

Anterior lateral microtubule cells, touch receptor neurons.
Neurons associated with ALM, send processes into tailspike.
Amphid Amphid sensillum (S) Bilaterally symmetric chemosensory specializations located on the two lateral lips in the head involving a large hole in the anterior cuticle. Each amphid contains 11 chemo and odorsensory endings and an apparent thermosensory ending. The cilia of the 8 of the chemosensory neurons extend out to the amphid pore whereas the endings of the three odorsensory neurons as well as the ending of the thermosensory neuron are enclosed by the amphid sheath cell.
Amphid cap cell Amphid socket cell (S)

Older name for amphid socket cell.

See Amphid socket cell

Amphid channel

Amphid lining (S)
Amphid pouch (S)

A narrow enclosed space formed by the amphid sheath and socket cells. The ciliated dendrites of the amphid chemosensory neurons are bathed in the fluid in this space that is continuous with the exterior environment via the amphid pore. The space is filled with an electron dense matrix material that surrounds the cilia. A similar (narrower) phasmid channel is formed in the tail by homologous cell types. A longer, more open canal, the spicule channel, encloses the spicule in the male tail, and is again formed by a sheath and socket cell. Unlike the amphid and phasmid channels, the spicule channel is lined with cuticle.

See Phasmid channel
See Spicule channel
See Accessory cells

Amphid commissure Hemizonid (S)

A large bundle of nerve processes which exit ventrolaterally from the amphid neuron cell bodies and then travel circumferentially under the ventral body muscles to reach the ventral nerve cord, where each amphid axon turns anteriorly to enter the nerve ring and deliver synaptic outputs to interneurons. The term can refer to the course of any one axon within the bundle, or to the bundle as a whole.

Because the commissure is so large and close to the cuticle, it can apparently be seen by light microscopy in larger nematodes, where it is known as the “hemizonid” (Bird and Bird, 1991).

Amphid gland Amphid sheath (S)
Amphidial gland (S)
Sensillar gland cell (S)
See Amphid sheath cell
Amphid nerve   A prominent fascicle of dendrites extending from the amphid sensilla to the cell bodies of the amphid neurons, containing single unbranched processes from the amphid neurons and also those of the related sheath and socket cells. There are virtually no synaptic contacts within this nerve.
Amphid neuron   Each of the 12 neurons that make up the amphid sensillum along with the support cells. These neurons are: ADF, ADL, ASE, ASG, ASH, ASI, ASJ, ASK (chemosensory neurons); AWA, AWB, AWC (odorsensory neurons); AFD (thermosensory neuron).
Amphid pocket cell Amphid sheath cell (S)

Older name for amphid sheath cell.

See Amphid sheath cell

Amphid pore Amphid opening (S)

The tips of the sensory dendrites of the amphid cilia are exposed to the outside environment via a narrow opening in the cuticle at the lateral lips, the amphid pore. Each pore is formed by one of the amphid socket cells. The pore may be obstructed or closed in certain mutants.

Amphid pouch Amphid channel (S)
Amphid lining (S)

See Amphid channel

Amphid sheath cell


Amphid gland (S)
Amphid pocket cell (S)


Accessory cells of the amphid sensillum. The sheath cell of the amphid is very large and contains distinctive secretory vesicles that are released into the amphid channel. This secretion may also spill out of the amphid pore to coat the nose of the animal (Bird and Bird, 1991).

Amphid socket cell


Amphid cap cell (S)


Accessory cells of the amphid sensillum. The anterior process of this interfacial epidermal cell encircles the amphid opening on the left or right lip of the snout, binding tightly to the hypodermal cells (hyp2 and hyp3) and to the amphid sheath cell by adherens junctions.

Amphidelphic   This term describes the reproductive tract of C. elegans, in which two equivalent ovarian arms extend anteriorly and posteriorly from a single vulval opening. Some other nematode species have a single ovary and are termed “monodelphic” and “prodelphic” since their single gonad is positioned anterior of the vulva. Other species may have two completely separate ovarian systems (didelphic), and yet some others have more than two ovaries extending from the same vulval region. There are species within Strongylida with both ovaries anterior of the vulva (didelphic and prodelphic) and there are also nematodes with the vulva near the mouth which consequently is didelphic and opisthodelphic.
Amphimictic / Amphimixis  

Describes a species in which sexual reproduction involves the mixing of eggs and sperm from different individuals. This trait is not always true in C. elegans, since the hermaphrodite can fertilize itself by mixing germ cells produced internally.

See Automictic
See Dioecious

Ampulla   An enlarged extracellular space through which the dorsal g1 gland cell duct opens into the pharyngeal lumen.
Anal depressor muscle

mu anal

Depressor ani (S)
Dorso-rectal muscle (S)


A single muscle cell lying above the anal ridge of the hermaphrodite tail that is in position to widen the anal opening for defecation. In the male tail this muscle cell becomes reorganized in the adult to open the cloaca.

See Defecation motor program

Anal papillae  

This term is a carryover from the older nematode literature, but it has rarely been used with regard to C. elegans. It refers to sensory receptors in the tail other than the phasmids, but it is not clear how broadly it applies in this species. In the hermaphrodite, the postdeirids lie somewhat too far anterior, and don’t seem to form a visible papilla when viewed by SEM so far (Hall, unpublished).

There are definitely papillae present in the developing male tail; the hook and postcloacal sensillum possibly qualify and are retained in the adult male tail, while the developing rays have an intermediate stage during late L4 in which they form papillae (Hall, unpublished).

Anal ridge   A robust chain of hypodermal cells, such as hyp10, hyp9, hyp8 and K’, extending from the tail whip forward into a ventral position and projecting centrally in the region above the anus and rectum, where it terminates in contact with the dorsorectal ganglion.
Anal sphincter muscle

mu sph

Rectal valve muscle (S)
Rectal sphincter muscle (S)


A smooth muscle formed by a single cell (mu sph) which encircles the rectal valve and whose contractions likely close the valve.

See Sphincter muscle
See Defecation motor program


The subdivision of M phase during mitosis or meiosis during which the chromatids separate from one another and move to the two ends of the spindle.

Anchor cell


gon herm anch

Z1.ppp or Z4.aaa


A cell in the somatic gonad that plays a key role in organizing vulval patterning and morphogenesis in the hermaphrodite; the preAC cell is the source for a secreted signal, LAG-2, which drives the AC/VU decision, which in turn determines the patterns of cell divisions among vulval precursors (reviewed by Greenwald, 1997). Through a feedback mechanism, the mature AC becomes the highest source of LAG-2 secretion, inhibiting LAG-2 production in VU.

In the male gonad, the anchor cell plays a much different role, as the gonadal leader cell during outgrowth, much as the DTC guides the outgrowth of the hermaphrodite gonad.

See AC/VU decision
See Distal tip cell
See Linker cell
See Somatic primordium

Andric index / Andric ratio   A measure of the rate of spontaneous males in a wild species of nematode. Bisexual species tend to support nearly equal numbers (Andric index near 50%), whereas hermaphroditic species (or races) tend to support very low rates of males. In C. elegans, the andric index is roughly 0.2% but can be considerably higher in some him mutants or after heat shock.
Androdiocey/ Androdioecious  

A breeding population in which males and hermaphrodites coexist (Stewart and Phillips, 2002).

See Dioecious

Aneuploid / Aneuploidy   Refers to any condition in which cells contain an abnormal number of chromosomes compared to the normal status for that time in development (euploid status). Thus, it can refer to multiple copies of chromosomes (e.g. trisomy, tetrasomy), free duplications, or loss of full chromosomes.
Annulus / Annuli (/pl) Annulation (S) Regular periodic specialization of the cuticle, forming shallow and deep transverse indentations of the outer surface of the cuticle. The deep indentation is known as an annulation or annulus. The thicker region of cuticle between two annuli is known as the “annule”. Other nematode species have similar deep indentations running lengthwise in the cuticle, called stria (Chitwood and Chitwood, 1950).
Anoxia Anaerobiosis (S)

A complete absence of oxygen in the culture medium (0% O2), under which C. elegans enters a reversible state of “suspended animation” or cryptobiosis (Van Voorhies and Ward, 2000; Padilla et al., 2002).  Under anoxic conditions the animals cease all movement, cell division and cell development.

See Cryptobiosis
See Hypoxia

Antagonist Agonist (A)

1) A chemical compound that inhibits the effect of a ligand, hormone or drug.

2) A muscle whose contraction counteracts the contraction of another muscle.

Anterior ganglion   A cluster of neuron somata located close to the nerve ring. Several other similar ganglia are associated with the ring, including the left and right lateral ganglia, the retrovesicular and ventral ganglion. Each of these ganglia contributes their axonal processes into the nerve ring, but maintain no zone of neuropil outside of the ring.
Anterior intestine   Portion of the intestine that is closest to the pharynx. The anterior intestine is connected to the pharynx via the pharyngeal-intestinal valve.
Anterior/posterior axis A/P axis The longitudinal axis of the extended body of the worm, or the major axis of the early embryo.
Anthelminthic   A drug used to expel or kill parasitic worms from the host organism.
Anus   The caudal opening of the rectum in the hermaphrodite tail.
Apary   This is technical term for the naturally occurring egl phenotype. In quite a number of species it is frequently observed that under certain conditions females don't lay all eggs and the hatching juveniles eventually eat their mother.
Aphasmidia Adenophora (S) A major classification of nematode species, grouped on the basis of their lack of caudal phasmids. Most of these species have caudal or epidermal glands, a single cell secretory/excretory system with a duct which lacks a cuticular lining, well developed amphids behind the labia, cephalic and somatic setae, and occur commonly in aquatic environments (Bird and Bird, 1991). Few species among the Aphasmidia are parasitic.
Apical constriction  

A distinctive shape change noted in some embryonic cells just prior to ingression during gastrulation, where the apical cell cortex shortens due to actomyosin contractions (Nance et al., 2005).

Apical ring Central cylinder (S) A cytoskeletal specialization within the proximal segment (basal body) of the cilium of many sensory dendrites where a narrow cylinder confines seven singlet microtubules which attach to its inner surface and nine (or fewer) doublet microtubules which attach to its outer surface; this cylinder of cytoskeletal material appears as a thin ring in cross-section (Perkins et al., 1986).

The first step in molting, during which time the old cuticle separates from direct contact with the hypodermis, in order to allow for the deposition of new cuticle underneath it.

See Molt

Apomorphy Plesiomorphy (A)

An evolutionary term describing a derived characteristic arising in the descendents of a species making it different from its ancestors.

Apoptosis Programmed cell death (S)

A common form of cell death which appears to originate as a decision within the nucleus to initiate a cascade of cellular events inside both the nucleoplasm and the cytoplasm resulting in chromatin clumping, nuclear breakdown, cell shrinkage and eventual death. Unlike necrotic cell death, apoptosis does not generally spread to neighboring cells.

See Necrosis
See Phagocytosis

Approach behavior Avoidance behavior (A)

A positive taxis in which the nematode reduces its probability of turning to move towards the stimulus (Miller et al., 2005).

AQR cell AQR QR ap Neuron, rudimentary cilium, projects into ring.
Arcade cell(s) arc ant
arc post
Interfacial cells between the pharynx and hypodermis which connect the hypodermal epithelium of the lips to the pharyngeal epithelium, firmly binding the inner tissue (the pharynx) to the outer bodywall (the hypodermis). Form anterior part of buccal cavity.
Area restricted search ARS

A foraging strategy in which the animal varies its turning frequency to maximize the time spent in places where resources (food) are abundant (Hills et al., 2004). When the animal senses the presence of food, it turns often, and tends to dwell in the same region. But as the time since the last food encounter lengthens, the animal turns less often, causing it to move in a straight line towards a new locale where food may be encountered once again. In C. elegans, ARS behavior seems to be evoked by food (chemosensory) signals but not by touch, and requires glutamatergic, octaminergic and dopaminergic signaling among head neurons (Horvitz et al., 1982).

See Basal slowing response


1) Extended lobes of the gonad in both males and hermaphrodites. In hermaphrodites gonad arms include the uterus, spermatheca and gonad sheath (which together constitute the “proximal arm”) and the unsheathed germ cells and distal tip cell (which together constitute the “distal arm”). The distal and proximal arms of the gonad connect via the “loop” region.

2) Distinctive processes (muscle arms) formed by each bodywall muscle in order to reach major nerve cords where they receive all of their synaptic input from motorneurons.

Arrest stage  

The typical developmental endpoint (early zygote, lima bean stage, young L1 larva, sterile adult, etc) that is achieved for a particular mutation or condition that leads to arrested development.

See Embryonic arrest
See Monster

Arrested development   See Dauer
See Diapause
See Quiescence
AS cell(s)


AS motor neurons (S)
DAS motor neurons (S)

P1 apa
P2 apa
P3 apa
P4 apa
P5 apa
P6 apa
P7 apa
P8 apa
P9 apa
P10 apa
P11 apa

Ventral cord motor neurons, innervate dorsal muscles, They have no ventral counterpart, and are cholinergic. Their connectivities are similar to VA neurons but receive additional synaptic input from AVB. AS neuron cell bodies lie within the ventral cord.

AS motor neurons DAS motor neurons (S) See AS cells

A family of very large parasitic nematode species, commonly studied by physiologists and pharmacologists due to the accessibility of its nerves and muscles by simple dissection.  Adult animals may range in length from 12-30 inches.


Nemathelminthes (S)
Pseudocoelomata (S)

A heterogeneous and large cluster of animals that have traditionally been classified together as a single group but later have been divided into about ten separate phyla, one of which is the Nematoda.

See Introduction to the Aschelminth Phyla

Amphid neurons, single ciliated endings, probably chemosensory; project into ring via commissure from ventral ganglion, make diverse synaptic connections in ring neuropil.
Amphid neurons, single ciliated endings, probably chemosensory; project into ring via commissure from ventral ganglion, make diverse synaptic connections in ring neuropil.
Amphid neurons, single ciliated endings, probably chemosensory; project into ring via commissure from ventral ganglion, make diverse synaptic connections in ring neuropil. Also take up FITC.
Amphid neurons, single ciliated endings, probably chemosensory; project into ring via commissure from ventral ganglion, make diverse synaptic connections in ring neuropil. Also take up FITC.
Amphid neurons, single ciliated endings, probably chemosensory; project into ring via commissure from ventral ganglion, make diverse synaptic connections in ring neuropil. Also take up FITC.
Amphid neurons, single ciliated endings, probably chemosensory; project into ring via commissure from ventral ganglion, make diverse synaptic connections in ring neuropil. Also take up FITC.
Associative learning  

A type of learning in which two stimuli that were previously experienced simultaneously become linked in the memory, such that encountering one of these stimuli provokes the animal to react as if it has now encountered the second, associated stimulus.

Asymmetrical cell division  

Asymmetric cell divisions play an important role in establishing the three main axes of the body and for separating various cellular components that help specific cell fate (for more detail see Gönczy and Rose, 2005).

See Symmetrical cell division

Asymmetry   A condition in which an object or parts of an object fail to show symmetrical configuration on the opposite sides of the central plane. Examples of asymmetry is noted in C. elegans in: 1) the overall layout of cell positions in the early embryo, 2) the portions of cell cytoplasm allocated to two daughter cells during mitosis, 3) the patterns of cell divisions (lineage) stemming from a blast cell, and 4) positions of certain tissues in larval and adult anatomy, such as nerve cords, mesodermal organs, etc.
Attachment plaque   The ends of the terminal (half) I bands where microfilaments are attached to the cytoplasmic surface of the plasma membrane of the muscle cell. Through these attachments each of the somatic muscle cells adheres tightly to adjacent muscle cells (Waterston, 1988). These electron dense plaques are also found in gonadal sheath cells where microfilaments attach to the plasma membrane (Hall et al., 1999). In vertebrates, attachment plaques are found in smooth muscle where they serve a similar function.
Attractant Repellant (A) A chemical moiety that causes an animal, a cell or a tissue to move towards that moiety.
Neurons, processes run with amphid neuron dendrites but lack ciliated ending.
Autofluorescent granule   A cytoplasmic structure that accumulates within certain cells, especially the intestine, as C. elegans ages. The content of these granules may include protein, lipid and/or carbohydrates, such as lipofuscin or rhabditin. They are often strongly fluorescent and not associated with particular organelles.
Automictic/ Automixis  

Describes a species in which reproduction involves the mixing of eggs and sperm generated from the same individual. This trait is true in C. elegans hermaphrodites, which can self-fertilize by mixing germ cells produced internally.

See Amphimictic

Autophagosome   A large membrane bound structure in intestine and some other cell types that may be involved in catabolic destruction of organelles. Material likely passes between the autophagosome and other endosomal structures, such as vacuoles or multivesicular bodies, as the contents of the autophagosome are consumed.

A process occurring within certain cells by which organelles or other cytoplasmic materials are degraded, using enzymes produced within that cell (for review see Kovacs et al., 2003). Molecular pathways controlling this process have been elucidated (Melendez and Levine, 2009; Kovacs and Zhang, 2010).

See Melendez and Levine, 2009 for more detail


In C. elegans, refers to any chromosome other than the X sex chromosome.


Refers to any animal that cannot supply a natural substance (such as an amino acid) necessary for its own growth, and therefore requires a nutritional supplement in order to survive and reproduce. Culture plates for C. elegans are usually made with a bacterial lawn of uracil-dependent E. coli; adding a limited amount of uracil within the medium of the culture plate forces a limit to the thickness of the lawn, since the auxotrophic bacteria fail to thrive once uracil is exhausted from the medium.

See Bacterial lawn

Ventral cord interneurons, synapse onto VA, DA and AS motorneurons; formerly called alpha.
Ventral cord interneurons, synapse onto VB, DB and AS motorneurons; formerly called beta.
Ventral cord interneurons, synapse onto VA, DA and AS motorneurons; formerly called delta.
Ventral cord interneurons, same post- synaptic targets as AVD, but processes restricted to anterior cord.
Aversion Avoidance (S)

A behavioral term, referring to the animal’s withdrawal or retreat from the neighborhood of a repellant or negative stimulus.

See Avoidance behavior

P1 aaaa
W aaa
Interneurons, processes in ventral cord and ring, few synapses.
AVG cell AVG ABprpapppap Ventral cord interneuron, few synapses, sends process into tailspike.
Neurons, mainly presynaptic in ring and postsynaptic in ventral cord.
Neurons, mainly postsynaptic in ventral cord and presynaptic in ring. Ring and ventral cord interneuron.
Neurons, mainly postsynaptic in ventral cord and presynaptic in ring. Ring and ventral cord interneuron.
AVL cell AVL ABprpappaap

Ring and ventral cord interneuron and an excitatory GABAergic motor neuron for rectal muscles. Makes few synapses. Functions in defecation; together with DVB, activates expulsion muscle contraction (E.p or EMC), also required for anterior body contraction (aBoc) step in defecation motor program.

See Defecation motor program

AVM cell AVM QR paa Anterior ventral microtubule cell, touch receptor.
Avoidance behavior Approach behavior (A) A negative taxis in which the nematode increases its probability of turning to move away from the stimulus (Miller et al., 2005).

See Thermal avoidance

AW (Amphid Wing) cells




Amphid wing cells, neurons having ciliated sheet-like sensory endings closely associated with amphid sheath.
Axenic medium  

A sterile medium on which one can grow nematodes without the presence of whole (live) bacteria, or any other living material.

See Defined medium
See Liquid culture
See Monoxenic medium

Axial core  

General region where homologous chromosomes pair with one another. This region includes the axial element and proteins associated with its pairing.

See Axial element

Axial element Chromosome cores (S)

Single proteinaceous axes of sister chromatids which polymerize in the assembly of the mature synaptonemal complex during meiotic prophase (Moses, 1968). The axial elements of homologous chromosomes become aligned and equidistantly separated by the proteins that constitute the central region of the synaptonemal complex (Zetka et al., 1999). It has been suggested that one role for the axial element is to hold the chromosome in a position so that preferred sites of exchange are exposed (Zetka et al., 1999).

See Central element
See Synaptonemal complex


A long thin process of a neuron, sometimes having distal branches, that forms synaptic outputs onto other neurons or muscles. Since many neuronal processes in C. elegans have mixed functions, not solely dendritic or axonal, these processes are more properly termed neurites.

See Dendrite
See Neurite

Axon guidance  

The mechanism by which a neuron process is stimulated to grow outward towards a particular signal or target cell, usually along the surface of a pre-existing cell or substrate. Axon outgrowth is typically led by a specialized structure, the growth cone. Dendrite outgrowth may occur by passive stretching as the animal enlarges (if the dendrite tip is well fixed to the cuticle) or by active outgrowth and guidance.

See Growth cone
See Pioneer axon

Axon Ring   An unusual structure formed by some individual pharyngeal axons in C. elegans to create a complete loop with itself; sort of a local self-syncytium (Albertson and Thomson, 1976).
Axonal transport   The mechanism by which vesicles and other organelles are translocated along the axon (neurite) towards or away from the cell soma. Active transport involves a microtubule based motor (kinesin or dynein family members) attaching to the organelle (the cargo) and the microtubule, and utilizing energy to move stepwise along the microtubule.
Axoneme   A distinctive bundle of microtubules and accessory proteins found within a cilium, often adopting a “9+2” organization in which 9 microtubular structures form a cylinder around 2 central microtubules. In a motile cilium, sliding of microtubules in relation to their neighbors can directly lead to bending of the entire structure. The axoneme is organized by a distal centriole in the dendrite. Axonemal microtubules often occur as doublets, with accessory proteins forming periodic arms extending between neighboring doublets.

The mechanism by which a neuron produces a new axon or axon branch, usually as a new outgrowth from the cell body led by the active outgrowth of the growth cone.

See Growth cone

Axoplasm   The cytoplasmic contents lying within a neurite process.

This section should be cited as: Herndon, L.A., Altun, Z.F. and Hall, D.H. 2009. Glossary A. In WormAtlas.  doi:10.3908/wormatlas.6.1
Edited for the web by Laura A. Herndon. Last revision: October 2, 2013.