A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 

Glossary - T




T cell

Tail precursor cell (S)


Tail lateral ectoblasts that give rise to neurons, hypodermis and glial lineages. While initially identical, after the L2 lethargus the T cell lineages become markedly different between males and hermaphrodites helping to provide the sexually dimorphic tail structures found in males.

T tubule Transverse tubule (S)

A tubular compartment found in vertebrate muscle cells, extending inward from the plasma membrane in the region near the sarcomeres, probably separate from the SER compartment. These tubules are thought to form a network of membranes that penetrate and span the cross section of each muscle promoting the propagation of contractile (electrical) signals from the surface membrane directly to the region of the muscle filaments. Identical structures have not been identified in C. elegans, but there is a component of sarcoplasmic reticulum in bodywall muscle which may serve parallel functions, running as thin tubules near the sarcomeres and the dense bodies.

See Sarcoplasmic reticulum

Tadpole stage 1.5 fold stage (S)

A "tadpole" looking embryonic stage in which the late gastrula consists of an enlarged anterior end (stomodeum) with a narrower, and more opaque, bit of tail lying just behind it within the eggshell. The elongation phase (and continued cellular morphogenesis) gradually converts the tadpole-like gastrula into a larval shape and the buccal cavity becomes apparent.


The most posterior region of the body. The anterior bound of the tail is ill defined though it might be marked as far forward as the position of the post-deirids, or as far posterior as the opening of the anus.

Tail bleb  

Any irregular swelling of the extreme tail tip, usually caused by a local defect in the normal smooth tapering of the hypodermis and/or cuticle.

Tail curling    

See Curl

Tail knob  

A common mutant phenotype in which the thin tapering of the tail whip is interrupted by a bulbous growth, often near the extreme tip (Rio-Albrectsen et al., 2006).

Tail seam


The more posterior members of the seam cells along the lateral bodywall which do not fuse with the hypodermal syncytium. In the adult male seam, the 3 most posterior members on each side (V5, V6 and T) follow a different cell fate from the other seam cells, acting as stem cells to create the sensory rays. In late L4 the posterior daughters of the ray precursor cells (R1.p-R5.p) fuse together, appear seam-like and are called the tail seam SET (Sulston et al., 1980). The tail seam does not produce alae.


Tail spike   ABplppppppa

A pair of short-lived hyp cells in the tail tip which fuse to form a syncytium and then form a slender bundle of filaments over which the tail tip cuticle forms. These cells undergo cell death after 6 hours, leaving behind a narrow spike of cuticle (Sulston et al., 1983). This thin cuticle specialization is often called the tail spike, while the cells may be called the tail spike cells. The posterior process of the tail spike has the appearance of a cilium filled with microtubules and wrapped by hyp10.

See Tail tip
See Scaffold cell

Tail tip Tail spike (S)  

The most posterior portion of the tail, usually referring to that portion lying posterior to the phasmid openings. In all hermaphrodites and in younger males the tail tip adopts a very long tapered shape ending in a thin spike that may represent some 10-15% of the total body length (proportionately longer in hermaphrodites than in young males). The tail whip is the finest, thinnest part of the tail tip, more flexible than that portion near the phasmids.

The tail tip is initially shaped by the tail spike cells which undergo programmed cell death late in embryogenesis and leave a narrow spike of cuticle.

During the maturation of the male, the tail tip undergoes retraction in late L4 stage and then hypodermal remodeling to form the fan, rays, bursa, and copulatory apparatus of the adult male tail. Sensory endings of the immature male tail (such as those of PHC and PLM) also become retracted and no longer extend into the posterior fan in the adult.

See Retraction
See Tail whip

Tail waving  

See Nictation

Tail whip  

The thinnest part of the tail tip of the hermaphrodite, at the extreme posterior end, which is so narrow that it easily bends and flexes upon itself as the animal moves. The tail whip contains a few putative sensory endings (PHC, nonciliated) surrounded only by a thin coating of hypodermis and the cuticle. These neuronal endings probably bend by 180° when the animal reverses direction, and may be activated by this bending.

See Tail tip

Tap response Tap reflex (S)  

A form of touch response that is elicited by repetitively hitting the culture plate to stimulate a behavioral response involving the touch dendrites. One can see this response by tapping the plate by hand, or hitting it against the microscope stage, but mechanical devices have been built to generate very reproducible repetitive taps (Rankin et al., 1990). It is an excellent means to study behavioral habituation and dishabituation (Rankin, 2005).


A form of chemosensation by which C. elegans can detect food and other environmental cues (Hilliard et al., 2004). Taste and olfaction have been used to learning and habituation assays (Jansen, 2005; Law and van der Kooy, 2005) .


An action that results in the animal orienting in response to a stimulus. This can be to move towards it (positive taxis) or away from it (negative taxis). Positive chemotaxis usually results in the animal traveling towards a higher concentration of a chemical signal. C. elegans has been shown to exhibit chemotaxis, phototaxis and thermotaxis. The regular motions of C. elegans on a culture plate may be a rather complex mixture of taxes and kineses (Dusenbery, 1980).

See Approach behavior
See Avoidance behavior
See Chemotaxis
See Galvanotaxis
See Kinesis
See Phototaxis
See Switched response
See Thermotaxis
See Tropotaxis


See Tooth


Archaic term for a lateral portion of the cloacal cuticle enclosing the spicule channels. It is sclerotized to reinforce the channel, and together with the gubernaculum, it helps to direct the spicule extension outward. Not clear how the telamon is separated from the gubernaculum, except that the gubernaculum proper lies more dorsal and medial.




The distal end of a linear chromosome arm. The two endpoints of each chromosome are characterized by distinctive repetitive DNA sequences (TTAGGC) of 4-9 kb which may act to cap each chromosome and protect them from fusion and degradation (Wicky et al., 1996). trt-1 has been identified as the C. elegans telomerase reverse transcriptase and is required to maintain telomere ends through successive generations (Meier et al., 2006). While it appears that organismal adult life span is independent of telomere length (Raices et al., 2005), maintenance of telomere length is required to preserve germ line immortality through successive generations (Ahmed and Hodgkin, 2000).



  A subdivision of M phase, during mitosis, during which separated daughter chromosomes concentrate at the two mitotic spindle poles and become surrounded by the reformed nuclear envelope.

A specialized cuticle formed by the telostom, covering the lumen of the pharynx at its junction with the buccal cavity, probably formed by the pm2 muscles of the pharynx. This zone forms a prominent constriction where the pharyngeal lumen is much narrower than the buccal cavity.

Telostom End cavity (S)

Previously known as the glottoid apparatus (archaic), it is the caudal portion of the buccal cavity, in register with the pharyngeal muscle cells pm2.

See Cheilostom
See Prostom

Temperature shift analysis


An experiment in which the developing nematode or mature animal is transferred from one environmental temperature to another in order to induce or prevent a temperature sensitive event, usually due to changes in gene expression or protein folding caused by the altered temperature. Such temperature shifts are often used sequentially on parallel populations to determine a “critical period” during which the event can be induced or repressed by the temperature shift.


An extended flexible extracellular matrix component that interconnects the basal laminae of two different nematode tissues.  Such tendons (sometimes called “flexible tracks”) have been observed connecting the pharyngeal lamina to the lamina of the outer bodywall muscles (Bumbarger et al., 2006; Axäng et al, 2007), and contain hemicentin and fibulin molecules (Vogel and Hedgecock, 2001; Muriel et al., 2005; 2006).

Terminal bar    

Archaic term for a prominent form of adherens junction, more commonly called a belt desmosome or zonula adherens.

See Adherens junction

Terminal bulb Postcorpus (S)
Posterior bulb (S)
Second bulb (S)

A major subdivision of the pharynx, lying between the isthmus and the pharyngeal valve. The bulb contains several large radial pharyngeal muscles, some neurons, and three large gland cells (Albertson and Thomson, 1976).

Terminal differentiation


A cell’s exit from the cell cycle and final steps in differentiation into a mature member of a given tissue. Dividing blast cells generally show little or no cell specializations and remain capable of further cell divisions. In contrast, cells following a “terminal differentiation" path seem to lose the capability to divide further, while adopting a final, specialized fate such as a neuron, muscle or intestinal cell.

Terminal duct

Excretory duct (S)


The secretions from the excretory system empty through this cuticle lined duct and pore located on the ventral side of the head.

Terminal phenotype Arrest stage (S)

Physical characteristics of an animal or tissue at its ultimate stage of development (for normal, wild type animals) or at the latest stage of aberrant development (for a mutant animal). In developmental mutants, the terminal phenotype is often characteristic of a particular subset of mutations and analysis may reveal an underlying developmental step that has been interrupted by those mutations.

See Embryonic arrest
See Monster

Terminal web  

A dense matrix of cytoskeletal proteins lying in the apical cytoplasm of intestinal cells, bounding the base of the microvilli. The terminal web forms a strong continuous sheet covering the entire apical zone, connected via adherens junctions to the terminal web in adjacent intestinal cells. Also found surrounding the lumen of the excretory canals.

See Brush border



That portion of the reproductive tract in the male animal in which the germline is mitotic or meiotic, also known as the germinal zone. This usually also encompasses the portion which is distal to the vas deferens: the zone touching the DTC, the bare zone and the zone covered by the seminal vesicle.

Some authors do not include the mitotic region as part of the testis, but define the spermatogonial region separately as the earliest structure, then the meiotic testis (seminal vesicle), followed by the vas deferens and cloaca (after Achanzar and Ward, 1997).

See Spermatogonial testis



A physical linkage of an organelle to the surroundings by a string-like molecule (cytoskeletal element), much as a balloon is said to be tethered to a fixed point by a piece of string. A “tethered” organelle may thus be fixed in place by this cytoskeletal linkage, or it may be dragged through the cytoplasm to a new locale via a tether to a cytoskeletal motor protein, such as a kinesin. Where multiple tethers are present, an organelle’s overall shape may also be controlled or deformed.


A distinct category of touch sensation. While it has been noted that C. elegans exhibits a basal slowing response to the presence of bacteria, they were also found to slow their rate of locomotion in response to the presence of a matrix of sterile beads indicating a mechanosensory rather than chemosensory response to their presence (Sawin et al., 2000). Additionally, this response requires serotonin and functioning dopaminergic neurons (Sawin et al., 2000).


Parthenogenesis (S)

Describing the asexual production of a population consisting only of females. Parthenogenesis is a common condition in some nematode species, but not in C. elegans except as a mutant phenotype.

See Parthenogenesis

Thermal avoidance

Heat avoidance (S)


A form of negative thermotaxis in which the animal backs up when encountering a point source of high temperature (such as a hot scalpel or laser to heat the substrate) (Wittenburg and Baumeister, 1999).




A temperature-induced change in the rate of body motion that does not involve a reorientation of the body to the temperature gradient.

See Kinesis
See Thermotaxis

Thermoreceptor Thermosensory ending (S)  

The highly branched microvilli of the left and right AFD dendrites are believed to be used in temperature sensation (Cassata et al., 2000; Inada et al., 2006).


The ability to detect changes in temperature. C. elegans migrate along thermal climes and this behavior appears to be regulated by a single pair of sensory neurons (AFD). Nematodes tend to prefer temperatures where they find food. This behavior is so strong, that it can be used as a learning paradigm since, if deprived of food at a given temperature, C. elegans will then avoid this temperature when placed upon a thermal gradient (Mohri et al., 2005).

For more information see review by McKemy, 2007.

See Thermotaxis



A behavior in which the animal orients to a temperature gradient and chooses to either move towards warmer conditions (positive thermotaxis, or “up" the temperature gradient), towards colder conditions (negative thermotaxis, or “down" the gradient), or chooses to move along a course that avoids warmer or colder conditions (isothermal tracking) (Hedgecock and Russell, 1975; Mohri et al., 2005; Mori, 2005) .

See Avoidance behavior
See Taxis

Thermotaxis circuit    

The set of synaptic connections that modulate the animal’s response to temperature gradients, involving the thermosensory cell AFD. Temperature activation of AFD stimulates the interneuron AIY which activates the interneuron RIA. AIZ interneuron is also involved, but acts to inhibit RIA (Mori and Oshima, 1995).


A reduced susceptibility to heat shock. As an individual's thermotolerance typically declines with age, an increase in thermotolerance is often correlated with increased longevity (Lithgow et al., 1995) and has even been used as a way to screen for long-lived mutants (Sampayo et al., 2000). A greater level of thermotolerance can also be induced as a pretreatment with a mild heat shock provides a level of heat shock resistance in the animals upon later exposure (Yashin et al., 2001).

Thick filament



A robust elongated cytoplasmic filament composed principally of myosin protein. In C. elegans, thick filaments also contain paramyosin (unc-15) and twitchin (unc-22). These filaments assemble with actin to form the actomyosin filament lattice within muscle cells which is anchored to dense body structures (at actin filament endpoints) to form the basis of the “sarcomere” which provides force generation due to the sliding of thick filaments vs thin filaments within the lattice.

When cytoskeletal proteins are compared in cross section, thin filaments <  intermediate filaments < thick filaments < microtubules.

See Actin
See Myosin
See Paramyosin
See Twitchin


Movement, inhibition of movement, or change in movement (velocity or direction) in response to contact.

Thin filament Actin (S) Microfilament (S)  

An extremely thin elongated cytoplasmic filament, usually composed principally of actin protein, which can assemble into any of several distinct forms, including a gel-like meshwork (g-actin), a tight bundle of parallel fibers (larger bundles are often called stress fibers, smaller bundles are often called f-actin), or can be interspersed with other filamentous proteins (e.g. myosin) to form a myofilament lattice, as in muscle cells. These forms of filament are each an important member of the “cytoskeletal proteins” which physically hold the cell’s organelles to one another internally, and which connect via plasma membrane attachment plaques (intercellular junctions) to hold cells together into a coherent tissue. The actomyosin (actin + myosin) lattice is especially important in force generation in all muscles.

When cytoskeletal proteins are compared in cross section, thin filaments <  intermediate filaments < thick filaments < microtubules.

See Actin 


Swimming (S)


A typical form of locomotion seen in nematodes when placed into an aqueous environment. The whole body makes large repetitive body bends, ventral, then dorsal, causing whole body flexions that leave the animal almost in place rather than swimming quickly forward or backward. Thrashing motions may be under similar motor control as crawling behavior on a solid substrate, but the pattern of muscle contractions underlying the behavior is different, since the rate of thrashing motion is about 5 times faster and the waveform has a different shape (Crofton, 1971; Faumont et al., 2005).

See Crawling
See Locomotion
See Swimming

Three-fold stage Loop stage (S)  

A late stage in embryogenesis during which the elongating embryo has begun to adopt a worm-like shape within the eggshell, and many events in tissue morphogenesis are proceeding. This stage immediately precedes the early pretzel stage.

Tight junction


Although no intercellular junctions have yet been shown morphologically to correspond well to a mammalian tight junction (TJ) at high resolution, some forms of adherens junction (AJ) make very close contacts, and molecular data suggest that C. elegans AJs share some components with TJs, perhaps serving purposes in C. elegans that would be divided between two distinct cell appositions in higher animals.

Some early workers have identified AJs to be tight junctions (for instance, Nelson et al., 1983), and this terminology remains in use by some workers (Shaye and Greenwald, 2002).

In older literature, this term was occasionally used erroneously to refer to gap junctions. High magnification TEM is required to properly distinguish them.

See Adherens junction
See Sealing junction
See Secretory-excretory junction

Titin Connectin (former name in vertebrates)

A giant polypeptide found in bodywall muscles in C. elegans that extends along the full length of a sarcomere. It is subject to high degrees of stretch without breakage, and is proposed to regulate the maximum length of the sarcomere during relaxation (Benian et al., 1996). A member of the family of “cytoskeletal elements”

Tonofilament Tonofibril (S)

An aggregation of intermediate filament proteins in parallel that forms a broader, stronger filament, common in various cell types including muscles. Tonofilaments have been identified in some marginal cells in C. elegans pharynx (Albertson and Thomson, 1976; Bartnik et al., 1986).

See Stress fiber

Tooth/ Teeth



This term can have several meanings:

1) A set of cuticular projections which meet within the second bulb of the pharynx (the grinder) and which must be used to break apart food particles.

2) A trio of cuticular flaps (buccal teeth or onchia) that project into the lumen at the posterior end of the buccal cavity to govern intake and outtake from the pharynx, but do not seem suited for tearing food in this species. They can be substantially larger and more functional in some other nematodes.

3) In some nematode species, there are “teeth” projecting from the vulva, appearing during at a late stage of gonad development, which help the female to grab onto a sexual partner.

See Odontostyle

Toroidal cells



Several cell types form elaborate concentric or consecutive toroidal cell groups, usually as cell fusions to form elongated tubular structures. The uterus is an elongated thin tube formed by consecutive toroidal ut cells groups which create four consecutive epithelial rings, ut1-ut4; similarly the vulval epithelium consists of seven toroidal cell groups, vulA-vulF, which begin as concentric rings on a flat epithelium and later telescope inward (evert) to produce a tube of seven consecutive toroidal rings lining the vulval passageway.

See Arcade cell


Sluggish in motion or functioning.

See Lethargus


The animal can sense several distinct classes of mechanical stimulus (touching) that are likely defined by the several classes of mechanoreceptor neurons spread over the body. Chalfie has defined several categories of touch: gentle touch to body, harsh touch to midbody, harsh touch to head or tail, nose touch and texture (see Hart, 2006 and Goodman, 2006) .

Gentle touch seems to be transduced by the “touch dendrites” ALM, PLM, AVM, and PVM. Reversal of body motion is achieved by stimulating receptors in the head or tail.

Harsh touch (such as by poking with a wire) is sensed by other receptors (PVD and perhaps FLP) in the head, along the midbody and in the tail (Chalfie and Wolinsky, 1990; Hart, 2006).

Nose touch is sensed by ASH, FLP and OLQ neurons (Kaplan and Horvitz, 1993).

Texture is sensed by CEP, ADE and PDE dopaminergic neurons and the serotonergic NSM neurons (Sawin et al., 2000).

The male tail also has sensory receptors that respond to touch. There are nine pairs of sensory rays, and several more post-cloacal receptors that help the male to sense the physical presence of the vulva during mating.

See Habituation
See Harsh touch
See Light touch
See Nose touch
See Tap response
See Texture

Touch cell

Mechanosensory neuron (S)
Touch neuron (S)

Refers to six neurons  (ALML/R, PLML/R, AVM, and PVM) that transduce light touch to the body by their distinctive microtubule-filled processes, or touch dendrites.

See Touch dendrite
Touch circuit    

The synaptic interconnections that link the mechanoreceptor neurons to local interneurons and motorneurons which drive forward and backward body motions of the whole animal (White et al., 1986; Chalfie et al., 1985; Goodman, 2006).

Touch dendrite Mechanosensory process (S)
Touch process (S)
Touch receptor (S)

The extended neurites of six neurons (ALML/R, PLML/R, AVM, and PVM) that transduce light touch to the body by their distinctive microtubule-filled processes that lie very close to the external cuticle, and that are linked periodically by dense deposits of mantle protein to the cuticle. Shearing forces upon these linkages are likely transduced by the nerve cell membrane as light touch (O'Hagan et al., 2005).

See Touch cell

Touch receptor Touch receptor neuron (S)

See Touch dendrite

Touch response Body touch response (S)

The behavioral change in body motion that occurs when one or more of the touch dendrites receive stimulation, for instance by stroking the animal with an eyelash (e.g. “light touch”) (Chalfie and Thomson, 1982). Light touch to the anterior body results in active reversal of body motion or backing behavior, while light touch to the posterior body results in an increased rate of forward motion.

See Harsh touch




A linear (or convoluted) route of outgrowth, restricted flow, or guided sequential processing. For instance, a nerve or fascicle may be called a process tract, the alimentary system is often called the digestive tract (pharynx, intestine, rectum), and the reproductive system is called the reproductive tract (germarium, sheath, spermatheca, uterus, vulva).




The detailed path followed by a moving object. Changes in direction along this path are often termed decision points (Hedgecock et al., 1987).


The set of all messenger RNAs (transcripts) produced in a cell or population of cells. Often this term is used to refer to the total set of transcripts from an entire organism. DNA microarray technology has helped develop transcriptome profiles of C. elegans at different developmental times, under different environmental conditions and in different tissues (Shin et al., 2008).

See Genome
See ORFeome
See Proteome


A mechanism for the transport of materials across an epithelial layer by:

1) endocytosis at one cell border (engulfment)

2) directed migration of the materials through the cytoplasm

3) exocytosis of the materials at the opposite border

Trans-Golgi network TGN

The final portion of the Golgi stacks through which vesicles progress and where they are packaged and sent to their proper destination.

Transition zone  

A portion of a dendrite cilium in which the cell process generally becomes surrounded by an accessory cell’s wrapping process, and where the internal cytoskeleton undergoes significant changes in organization.

1) The term may refer to the proximal base of the axoneme where it is anchored to the plasma membrane by Y links. This portion of the cilium has sometimes been loosely referred to as a basal body (Wright, 1980).

2) Alternately, a segment of the distal arm of the germline where germ cells progress from continued mitosis (in the more distal portion) and enter into the pachytene phase (in the more proximal portion under sheath cell 1) (Crittenden et al., 1994; Hubbard and Greenstein, 2000). It remains unclear whether the filapodial extensions of sheath cell pair 1 (Hall et al., 1999) touch the transition zone, or only the pachytene zone.

See Basal body

Transporter protein  

A membrane-associated macromolecule that serves to move certain categories of solutes across the membrane, from inside to the outside, or vice versa. Some transporters may constitute a patent channel in the membrane while others may enfold the solute molecules and carry them across the membrane.

Transport vesicle



A category of membrane-bound small vesicle that is specialized for moving components to the cell periphery (especially down the axon) in a cell, but which may require further maturation to become functional (for instance, before being competent as a synaptic vesicle).

See Vesicle

Transverse Transverse aspect (S)  

A plane of section (or angle of view) perpendicular to the longitudinal body axis. It is also called "cross section".


An inferred mechanism for amoeboid motion, in which the components at the leading edge of the pseudopod become attached to the substrate and then are translocated backwards along the bottom edge of the pseudopod, pulling the cell (or growth cone) forward, and then being released from the substrate to be internalized and recycled back to the leading edge (Roberts and Ward, 1982).

See Pseudopod elongation
See Sperm motility

Triadic synapse




A chemical synapse in which the presynaptic profile appears to have access to three postsynaptic profiles simultaneously; thus A --> B+C+D.

See Dyadic synapse
See Monadic synapse


A large rod-shaped protein closely associated with the actin thin filament in muscle cells (Miller et al., 1983).

See Thin filament




A protein complex associated with tropomyosin within the actin thin filament. It consists of three gene products, troponin T, troponin I and troponin C (TnT, TnI, TnC). Troponins are expressed with bodywall muscles and pharyngeal muscles in C. elegans, and may play a key role in actin/myosin interactions within the muscle sarcomere.

See Thin filament


Any locomotory behavior in which the animal orients its direction by comparing the signal strength at two paired sense organs simultaneously. Since nematode sensilla pairs tend to be left/right pairs, and the animal lies on its side (bringing both sensilla into virtually the same point in any gradient within the plane of body motion), tropotaxis seems an unlikely means to recognize any signal gradient, unless the animal compares signals between head and tail receptors (amphid vs phasmid).

See Klinotaxis
See Taxis

Tubular body  

Dendritic specialization within the CEP mechanosensillum.

Tubular radii Pharyngeal channels (S)

See Pharyngeal channels


Dark thin structures, “tubules”, form tight networks in several categories of pharyngeal muscle cells at regions of apparent neuromuscular synaptic contact. One pharyngeal neuron soma (M2) contains similar material. It is not clear whether these objects are solid or membranous (Albertson and Thomson, 1976). Dark vesicular structures are also found near these networks. These tubules were also called “striations” or “reticulations” by the same authors.

Tubule-associated material TAM

Electron dense material which lies in the cytoplasm of sensory cilia in close apposition to a microtubule bundle in several sensory neurons, including CEP, OLL and OLQ.



Tumorous germline  

A mutant phenotype in which germline proliferation continues unabated (through endless mitotic divisions) to produce an excess of immature germ cells, enlarging the gonad into a swollen tumorous organ which can distort the whole body of the nematode, or spill across the basal lamina to invade neighboring tissues (Wilson Berry et al., 1997; Kadyk and Kimble, 1998; Huang et al., 2003).

Turgor pressure Hydrostatic pressure (S)

The internal pressure of body fluids that is transmitted outward to the body cuticle in all directions to fully inflate the animal. In the nematode, the action of body muscle contractions utilizes turgor pressure to help spread their forces over the whole body length to produce a general undulatory motion. The excretory system may act to regulate salt balances in a manner that modifies turgor pressure which, when defective, can lead to animals with flaccid paralysis or rigid rod-like paralysis. High turgor pressure may generally lead to narrowing of all tubular organs, so that egg-laying and defecation require the action of dilator muscles to open the related passageways, and the use of spicules in male mating to open the hermaphrodite vulva (Nicholas, 1975).


C. elegans forward locomotion involves episodes of turning that are termed "pirouettes". These are "sharp" turns with the intervals of forward movement between them termed "runs" (Ringstad and Horvitz in Hart, 2006).

Turning is also a distinctive event during male mating behavior when the male reaches the edge of the hermaphrodite’s body and must continue backing along the other side of the hermaphrodite, in the opposite net direction in search of the vulva (Loer and Kenyon, 1993). Each turn can be scored as “good”, “sloppy” or “missed” according to how well the male remains in contact with the body of the hermaphrodite during the turning event (Loer in Hart , 2006). Some missed turns can be further subdivided into “swim off”, “wide turns”, or “stutter turns” (Emmons in Hart, 2006).

Twitcher phenotype  

A defect in some unc mutants (ie. unc-22) in which individual muscles or local portions of one muscle quadrant show rapid, independent contractions, superimposed on the well coordinated smooth motor contractions pass along the length of the body, that characterize normal body motion.


See Titin

Two-fold stage

Plum stage (S)

A late stage in embryogenesis, by which time the embryo has lengthened to two almost equal lengths within the eggshell. At this stage the lengthening embryo is moving continuously within the eggshell.

Type A motoneuron Class A motoneuron (S)

DA, VA, & DAS (AS)

Type B motoneuron Class B motoneuron (S)

DB and VB

Type C motoneuron Class C motoneuron (S)


Type D motoneuron Class D motoneuron (S)

DD and VD

Edited for the web by Laura A. Herndon. Last revision: September 21, 2011. This section should be cited as: Herndon, L.A. and Hall, D.H. 2010. Glossary T. In WormAtlas.  doi:10.3908/wormatlas.6.20