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Glossary - S




S blastomeres

Somatic blastomeres

The original nomenclature of Boveri (1899) for the early cell divisions of the nematode embryo. S1 is now called AB, S2 is now EMS, S3 is C, and S4 is D.

Sagittal view  

Sagittal sections run from one side of the body to the other (left to right or vice versa) following the sagittal plane (Y-Z axis) that divides the body into right and left portions and is parallel to the median plane.


A characteristic jerky motion involving abrupt transitions between motion and immobility. Motions of a certain speed continue for short duration, alternating with periods of immobility. Such dynamics are typical of some objects under the control of molecular motors, whose activity may rapidly switch between ON and OFF states as is during axonal transport of dense core vesicles (Zhan et al., 2004).

Also can be used to describe the evolutionary theory that reveals discontinuous, large jumps in the evolution of a species (Sternberg and Horvitz, 1984).


Plasma membrane of a muscle cell, covering the outisde of myofilament network, the muscle belly and the muscle arms.


Spindle (archaic)  

A single functional unit in the contractile portion of a muscle cell. Body muscle is obliquely striated with multiple sarcomeres in repeating fashion. Pharyngeal muscle is radial but not striated, with only a few sarcomeres per cell. There are many specialized muscles in male tail and in the vulva which are diagonal but not striated, and often consist of only a single sarcomere. There are several muscle sarcomeres that are organized circumferentially, in particular, the sphincter and one of the uterine muscles.

Striations consist of oriented members of the myofilament lattice, which are anchored to dense bodies on the plasma membrane. The orientation of the lattice elements (oblique to the body axis, or diagonal, or radial) determine the angle of the striations and of the whole muscle. Some smooth muscles in the nematode appear to be organized without recognizable sarcomeres, such as the gonadal sheath and the sphincter muscles.

See Dense body
See Myofilament lattice
See Smooth muscle
See Z band

Sarcoplasm Muscle belly (S)  

Cytoplasm of any muscle cell, especially referring to that portion of the cell body near the nucleus.

See Muscle arm

Sarcoplasmic reticulum SR

A subset of the smooth endoplasmic reticulum which runs as thin membrane-bound tubules along the dense bodies of muscles. These tubules may sequester calcium ions for release during muscle contraction in response to nerve impulses. These structures are quite thin and appear discontinuous in thin section due to their tortuosity in C. elegans.

See Endoplasmic reticulum
SC knob


See Synaptonemal complex


This term can apply to similar structures at a variety of different levels, from tissues, to cells, to cell parts, to molecules.

Provided by sheath cell processes for axonal outgrowth (Antebi et al., 1997) and by GLRs for muscle arm outgrowth.

Alternately, the same term can refer to subcellular features. Some plasma membranes are reinforced by “scaffolds” either on the outside by 1) basement membrane on the basal surface, or by 2) glycocalyx on the apical surface, or 3) reinforced on the cytoplasmic side by surface coats made from cortical cytoskeleton, spectrin and cytoplasmic linkers, as well as a variety of uncharacterized molecules, many of which add visible electron density to the inner leaflet when viewed by TEM.

Cytoskeletal elements such as microtubules or intermediate filaments or PSD-containing subsynaptic proteins may be “decorated” by specific proteins over their length, thus acting as a scaffold onto which are positioned microtubule-associated proteins (MAPs), junctional proteins, synaptic receptors, etc.

See Basal lamina
See Glycocalyx
See Spectrin
See Undercoat

Scaffold cell    

A cell whose cell body and/or extended processes provide the substrate which acts to shape the differentiation of another tissue. Several different cell types fit this general description:

1) The GLR cell bodies mark the position at which head muscles project their arms inward and the GLRs’ extended processes act as the substrate over which these muscle arms form a thin cylindrical plexus or motor plate onto which the nerve ring motor neurons form neuromuscular junctions.

2) The spike cells of the tail tip, and their epithelial covering by hyp10, also fit this definition. The spike cell syncytium acts as a scaffold for a posterior extension of hyp10, while the hyp10 extension acts as a scaffold for the secreted spike of cuticle at the extreme tail tip.

3) The XXX cells of the lateral lips and their extended anterior processes seem to provide a scaffold for the early elongation of the ventral bodywall muscles, and for the separate paths of the amphid nerve and the mechanosensory nerves. They may also organize the relative positions of the various socket cells of the lateral lips.

4) The anchor cell (AC) of the vulva acts as a scaffold for the formation of the uterine seam (utse) in order to connect the vulval passageway to the two lobes of the uterus.

Sclerotic/ Sclerotized  

A local hardening of the cuticle, usually accompanied by distinctively darker, more electron dense specialization, sometimes running uniformly across the layers, or sometimes showing parallel striations across the layers. Such specialization is most dramatic at the hook and spicules of the male tail, which are used as physical anchorages during male mating behavior. They are also found in many other portions of cuticle that are subject to high stress, such as along the buccal and pharyngeal passageways and the grinder, or at the excretory pore.

SDS Sodium dodecyl sulfate  

A commonly used detergent which can kill all stages except dauers and some eggs. It is often used to clean contaminated cultures or to produce staged cultures.

Sealing junction

A subtype of adherens junction between neighboring sheath and socket cells whose apposing plasma membranes are exceptional tight, effectively sealing the internal pocket from contact with the pseudocoelom.

See Adherens junction

Seam cell  

This term most often refers to the hypodermal seam cells, which lie along the lateral bodywall to form longitudinal stripes of epithelial cells underlying the alae, and are apparently responsible for formation of the alae themselves (Singh and Sulston, 1978). These differentiated cells also act as blast cells that can later give rise to specialized sensory structures such as the male tail rays. In late larval development, the seam cells mature and fuse to form a continuous syncytium along the bodywall, separate from the hyp 7 syncytium.

The term can also refer to the uterine seam (utse), another epithelium that acts to bind the vulval epithelium to the uterine epithelium, forming a three-way junction linking the single vulval passageway to the anterior and posterior lobes of the reproductive tract. This structure is created by the fusion of several precursor cells, and initially forms over the anchor cell, which acts as a scaffold.

Searching behavior

See Foraging
See Leaving behavior
See Mate-finding



See Phasmidia

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

The most posterior portion of the pharynx which has an enlarged round shape. This is 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).

Secondary ectoderm    

Cells and tissues that form from the C lineage, principally comprised of posterior hypodermis and some neurons.

See Primary ectoderm

Secondary interneuron



A type of interneuron that lies downstream from primary interneurons, and which directs its own synaptic output to command interneurons, rather than motor neurons.

See Command interneuron
See Primary interneuron

Secondary mesoderm



The cells and tissues that form from the D lineage, consisting solely of some bodywall muscles.

See Primary mesoderm

Secondary oocyte    

The second most mature oocyte within the gonad, lying next to the primary oocyte.

See Primary oocyte

Secondary spermatocyte


The daughter cells that result from the meiotic division of the primary spermatocyte, which maintain a syncytial relationship via a common residual body. Secondary spermatocytes mature by transferring some materials to the residual body, after which they detach to form spermatids.

See Primary spermatocyte

Secretory cell    

See Excretory cell
See Excretory duct cell
See Excretory gland cell
See Excretory pore cell
See Gland cell
See Seminal vesicle
See Vas deferens

Secretory-excretory junction


Elaborate, highly specialized junctions where the excretory gland, excretory canal and excretory duct come together and join up to allow outflow of gland granules and canal urine into the duct. Perhaps a specialized form of adherens junction.

See Secretory membrane

Secretory-excretory system Excretory system (S)

Four cell types (1 pore cell, 1 duct cell, 1 canal cell and a fused pair of gland cells) make up the excretory system. The secretions of this system empty through the excretory duct and pore on the ventral side of the head. This system allows the animal to secrete saline fluid and maintain a proper salt balance. Other secretions, some postulated to play a role in molting, are also secreted.

Secretory granule


Secretory body (S)

A membrane-bound vesicle found in the cell cytoplasm containing stored material bound for export from the cell. The secreted material could be, among other possibilities, a hormone or signaling molecule, an enzyme or kinase, an energy store (yolk), or a glycoprotein destined for the glycocalyx or cuticle. Secretory granules are generally larger in dimensions than the secretory vesicles found in neurons. Granule contents may be delivered into the pseudocoelom, into the lumen of an epithelium, into a secretory duct or channel, into the external environment or the underside of the cuticle. Granule secretion is more often apical than basal.

See Granule
Secretory membrane

Excretory junction (S)


A specialized portion of the plasma membrane of the excretory gland cell to the excretory duct through which the gland releases the contents of its secretory vesicles, through a region in which the apposed membranes are also heavily reinforced by adhesive specializations on their cytoplasmic surfaces.

See Secretory-excretory junction

Secretory stack Lamellar membrane (S)

A specialized organelle on plasma membrane of apical hypodermis, possibly involved in cuticle deposition. It is almost always closely associated with a mitochondrion.

Secretory vesicle  

See Secretory granule


C. elegans does not show clear regional segmentation across tissues; however, there is a repeating pattern to the organization of many body systems that is reminiscent of segmental organization. The clearest regional demarcations are in the head and tail, where many tissues show local specializations that are unlike the body region. Some authors have further recognized “developmental regions” along the length of the body that are somewhat like segmental organization (von Ehrenstein and Schierenberg, 1980).



A category of adherens junction in which a cell forms a junction onto itself, usually in order to form a complete ring around another structure. This is a common feature in socket cells where they form a complete seal at the opening of a sensillum.

See Adherens junction

Self progeny Cross progeny (A)

Progeny that derive from self-fertilization of a spermatozoon and an oocyte from within the hermaphrodite gonad, not involving a mating event with a male animal.

Self propagation Selfing (S)

The act of internal fertilization of sperm and oocyte deriving from a single parent animal to produce self-progeny. Thus a single C. elegans hermaphrodite, living apart from any fertile partners, can produce over 200 self-progeny who derive all genetic material from the one parent.

Self sperm


Spermatozoa derived from the hermaphrodite germline and not from the male. These are typically smaller and less motile than sperm from a male.

See Sperm competition


Self-fertilization (S)

Most C. elegans are hermaphrodites and have this capability to produce “self-progeny” by internal fertilization, combining male and female gametes produced by the germline of the parent animal. This process is different from parthenogenesis, in which a new animal is produced from the fission of a single gamete by asexual means.

See Cross-progeny
See Inbred / Inbreeding
See Outcross

Seminal fluid



Fluid ejaculated by the male’s seminal vesicle along with the spermatozoa. It may contain soluble factors which activate sperm motility or sperm’s competence to fuse with the oocyte (L’Hernault, 1997; but see LaMunyon and Ward, 1995).

Seminal vesicle Proximal testis (S)  

Structure (in the male gonad only) which houses the maturing sperm cells prior to mating. It is a tube-like structure formed from 20 secretory cells that are surrounded by a sheet of cytoplasmic processes formed from 3 large cells. These somatic cells derived principally from Z1.pp or Z4.ap (Kimble and Hirsh, 1979).




Chemicals that mediate interactions between organisms. They are subdivided into allelochemicals (signaling to members of other species) and pheromones (signaling within the same species).

See Allelochemical
See Pheromone


An aberrant condition in which one “half vulva” (anterior or posterior) develops independently from the other due to loss of precursor cells for the other half (due to laser ablation or mutation).

See Pseudovulva
See Vulva

Sensillum/ Sensilla    

A sensory organ, generally made up of one or more sensory neurons whose dendritic endings are protected by one or two accessory cells, and a thin wrapping of hypodermis.

See Amphid
See Cephalic sensilla
See Deirid
See Labial
See Phasmid
See Hook sensillum
See Postcloacal sensillum
See Ray
See Spicule


A non-associative learning response where there is an increase in the magnitude of response following repeated administrations of a stimulus.

See Learning and memory

Sensorimotor neuron Polymodal neuron (S)

Neuron having a mixed modality of cell functions, including both sensory transduction (by its dendrite) and motor output (via its neuromuscular junctions).

See Mixed modality

Sensory adaptation  

The animal’s responsiveness to the prolonged or repeated exposure to a sensory stimulus (chemical taste, olfaction, osmotic barrier, temperature, touch) which usually shows a decrease. In most cases, upon removal of the stimulus, the sensory response will later recover (Jorgensen and Rankin, 1997). Olfactory adaptation is more complex, and some odorant responses do not adapt (Bargmann and Mori, 1997). These short term adaptations could be governed by changes in receptor responsiveness in the dendrite, or by changes in synaptic efficacy between sense cells and interneurons or motorneurons.

See Adaptation
See Habituation

Sensory cilia



The only ciliated cell type in C. elegans is the sensory neuron. Of the 302 neurons in the adult hermaphrodite, 60 of them are ciliated. Males have an additional 52 ciliated neurons, most of which are found in the tail (for detail see Inglis et al., 2007).

See Sensillum
See Sensory neuron

Sensory neuron    

Neuron that is involved in responding to external stimuli such as chemosensation (Bargmann, 2006), thermosensation, osmosensation or mechanosensation (Goodman, 2005).

Most sensory neurons are ciliated in structure (Inglis et al., 2007), except the touch neurons (ALM etc), the PVD neurons and perhaps a few others.

See Sensillum
See Sensory cilia

Sensory ray

Ray (S)


A long thin bristle-like specialization embedded in the fan cuticle of the male tail, consisting of extended processes of three cells (RnA, RnB, Rnst) - two ray neurons and a support (structural) cell, all wrapped within a thin layer of hypodermis. At the distal end the structural cell expands to form a pocket enclosing the ciliated endings of the two sensory neurons. At the tip there is a narrow pore which opens this pocket to the exterior to expose the cilia to the outside environment.

See Ray

Sensory receptor  

Each sense receptor organ, or sensillum, contains one or more ciliated nerve endings and two non-neuronal cells, a sheath and socket cell. Most receptors are located in the head, which is where most sensory functions take place. Some sensory “receptors” exist as diffusely localized membrane channels in one or more neuronal processes that do not involve a cilium (such as PVD’s highly branched arbor along the bodywall, or the diffuse sensory channels in an ALM dendrite).

See Sensillum

Sensory receptor ending  

Most ciliated nerve endings are either exposed to the environment via openings in the cuticle or they terminate or embed within the cuticle. Two unusual sensory neurons, AQR and PQR are exposed to the pseudocoelomic cavity of the worm. For detailed list see Table in Inglis et al., 2007.

See Sensillum
See Sensory receptor

Septate junction Pleated septate junction (S)
Pleated junction (S)
Continuous junction (S)

Usually refers to an intercellular junction found in the spermatheca and perhaps in the vulval epithelium. Here the two plasma membranes are separated by a distance to each other (the septum), and electron dense specializations mark the cytoplasmic borders in a “pleated” (ladder-like) pattern. The term can refer to both the pleated septate junction and to the continuous (smooth) septate junction, which displays a wide intermembrane spacing (is septated) but shows no visible pleating.

See Continuous junction


The division of a cavity into parts by a septum. Used to refer to a mutant phenotype of excretory canal cells where neighboring cystic portions of the lumen become partially septated (Buechner et al., 1999). Inside the uterus, the egg chamber may also have temporary septations separating one embryo from the next.


See Smooth endoplasmic reticulum



Seam cell syncytium (S)


SET refers to the five most posterior seam cells in the male, which fuse to form a syncytial compartment in the male tail, after the generation of the ray cell groups. Unlike the most anterior seam cells in the male which make alae, the SET cells do not make this cuticular structure.

See Tail seam
See Ala / Alae

Seta/ Setae Bristle (S)

Stiff bristle-like sensory features that occur in some nematode species, as opposed to shorter nipple-like sensory structures, known as papillae. In C. elegans, very few sensilla form true bristles (except for the spicules and perhaps the rays), but some shorter papillae are common (including the inner labials, cephalics, post-cloacal sensilla, and the hook sensillum).

See Papilla/ Papillae

Sex determination



C. elegans has two sexes. Hermaphrodites are diploid with five pairs of autosomes and two X chromosomes. Males have the same number of autosomes, but only have one X chromosome. Gametes produced by hermaphrodites are all haplo X so they give rise to nearly all XX hermaphrodite self progeny except for the rare male formed from X-chromosome loss. Males produce haplo-X and nullo-X sperm so cross progeny with a hermaphrodite will produce half male progeny.

Most differences between the sexes develop postembryonically by different cell-specific patterns of gene expression. In somatic cells, the sex-specific fate of different cells is controlled by the master regulator tra-1 which acts as a transcriptional repressor in hermaphrodites. In the germ line, regulatory interactions of additional genes are required to specify sexual fate.

For more information see chapters in Wormbook (Herman, 2005; Ellis and Schedl, 2007; Zarkower, 2006).

Sex muscle  

The muscles of the adult reproductive system. In hermaphrodites, these include the vulval and uterine muscles, located near the vulva in the midbody, which all derive from the M myoblast.

In adult males, the M myoblast gives rise to a much larger set of specialized muscles for male mating which differentiate within the tail region (See Male Muscles - Overview and Male-specific muscles).

Sex myoblast


Sex mesoblast (S) M cell (S)

In the hermaphrodite, the postembryonic blast cell, M, begins dividing during the L1 larval stage to produce bodywall muscles plus two daughter myoblasts. These two daughter myoblasts migrate within the body and divide during the L3 and L4 larval stages to produce the sex muscles of the vulva and uterus.

In the male, the same sex myoblast again gives rise to many bodywall muscles plus six myoblasts in the L1 stage. These six myoblasts migrate posteriorly and divide during L3 and L4 stages to produce the specialized mating muscles of the adult male tail.

Sex pheromone  

See Pheromone

Sexual dimorphism



Property by which different sexual forms of a species assume different body size and/or shape. C. elegans is moderately dimorphic in size, since males are slimmer than the hermaphrodites. They also have distinct anatomical differences. Externally, the adult hermaphrodite has visible vulva, while the adult male tail becomes reorganized in order to form a distinctive mating structure. The internal reproductive organs also differ between male and hermaphrodite and there are substantial changes in musculature and nervous system. Some other nematode species are much more dimorphic in size and shape.

The term can also be used to refer to alterations in the cell fate for a specific cell between the two sexes (such as the M myoblast). A specific cell may live and differentiate in one sex, but undergo cell death, serve as a blast cell or merely change shape in the other sex. These differences in cell fate (large or small) are also considered individual sexual dimorphisms.

Sheath Lining (S)  

This term has several distinct meanings.

An enclosed channel formed by the sheath and socket cells to house the distal components of sensory dendrites of a sensillum, or of an external structure such as the spicule.

A layer of epithelial cells that enclose another tissue, such as the gonadal (ovarian) sheath which encloses the germ line.

More commonly known as the embryonic sheath, a lipid layer covers the embryo before elongation and is thought to serve as a template for cuticle annulations. The first cuticle is made at L1 and replaces the sheath (Priess and Hirsh, 1986).

Additionally, the term has been used in nematode literature to refer to a shed cuticle [post-molting] that has been retained over a portion of the body, especially in the case of dauer formation (Yarwood and Hansen, 1969).

See Embryonic sheath
See Sheath cell
See Sheathed

Sheath cell Pocket cell (S)
Papillary gland (archaic)

An interfacial epithelial cell which forms a specialized environment surrounding the ciliated sensory ending(s) of one or more neurons and is often accompanied by a more distal socket cell. Some sheath cells also extend thin wrapping processes around bundles of axons in the nerve ring. In early development of the sensory nerves and of the nerve ring, some sheath cells (cephalics and labials) may also provide a substrate for axon guidance.

Another category of sheath cells (SPsh) encloses the spicule channel in the male tail and apparently secretes cuticle which lines the channel.

See Glia table
See Gonad sheath
See Ovarian sheath
See Socket cell
See Spicule
See Structural cell

Sheath channel Sensillar Pouch (S)  

The external space or cavity created by the sensory accessory cells (sheath and socket cells, or structural cell) that enclose the sensory cilia of most specialized sensory receptors. In chemosensory sensilla (such as in amphids), this space is open to the exterior environment via a pore created by the socket or structural cell, but in other cases the space is usually sealed closed beneath the cuticle (as in outer labial and cephalic sensilla).

See Amphid channel

Sheath lamellae  

A prominent feature in the amphid sheath cells, lying in the sheath process near the amphid pocket. This large flattened multilamellar structure is likely to be an enlarged Golgi apparatus, and appears to shuttle material to the pocket in small vesicles (Perkins et al., 1986). Smaller sheath lamellae are found in the sheath cells of other sensilla, including the cephalics and the phasmids.

Sheath receptors  

A term used to refer to those amphid cilia that end within the sheath or in cryptic locales (those of AFD, AWA, AWB and AWC), as opposed to those cilia that are directly exposed to the environment through the amphid pore (the amphid chemoreceptors).


The property of being confined within an extra cuticle layer. In some nematodes, early larval cuticle layers may be retained as outer sheaths, providing an added layer of protection from the external environment. Sheathed animals often cannot feed due to interference of the excess cuticle. “Exsheathment” defines the process by which the animal finally loses this layer or layers. Although wild type C. elegans is rarely, if ever, sheathed, some molting mutants can cause full or partial cuticle retention.

See Exsheathment


A typical nematode behavior in which the body becomes locally foreshortened without any bending motion. This is typically seen as a head withdrawal from an aversive stimulus to the nose, or as a shortening of the posterior body as part of the defecation motor program, but is seen in exaggerated form in the mutant shrinker phenotype.

See Shrinker phenotype

Shrinker phenotype  

A rather rare mutant behavior in which the whole body undergoes longitudinal shortening in response to head touch or tail touch. These animals are generally unable to generate normal body waves, and apparently lack reciprocal inhibition of the dorsal and ventral body muscles.


Cuticle projections (finger-like) into the pharyngeal lumen that form a meshwork which may act to filter or retain contents of the lumen. They lie within the metacorpus (1st bulb).

See Buccal filter

Single sarcomere muscle  

A category of specialized muscle cells in which all muscle filaments are organized into a single well ordered motor unit, with all thin filaments lying in close register to a single band of dense bodies on each end of the cell.  In C. elegans, this category includes many of the muscles of the male tail and the radial muscles of the pharynx.

See Radial muscle
See Smooth muscle
See Striated muscle

Sinus Excretory sinus (S)

An extracellular cavity or tube formed by an epithelium or within a single cell. While the term is usually used with regard to tissues involved in excretory or secretory functions, it can also refer to the lumena of the pharynx or digestive tract.

Sinusoidal wave  

The pattern of body motion produced as the whole animal crawls forward. The muscles on one side contract while the muscles directly opposite relax in synchrony such that a smooth wave of contraction passes along one side of the body to cause a smooth deep bend in the body.

See Locomotion


See Paternity

60o fibers GLR cell (S)

Archaic name for the cell extension of the GLR cells whose projections run just under the nerve ring. These 6-fold cells each run about 60° around the ring and thus encircle the whole isthmus (6 x 60 degrees = 360) (Ware et al., 1975).


Hypodermal system (S)

This term is rarely used in C. elegans literature (See Podbilewicz, 2006).

Sloppy turn  

See Turning

Slow killing  

A mode of toxic interaction in which a bacterium invading the host nematode does not quickly poison or kill the host, but chooses to colonize the animal and reproduce itself for an extended period prior to toxin production (Darby, 2006).

Small phenotype


Produces a “miniature” adult worm, as opposed to a “dumpy” phenotype, in which a more normal sized adult worm seems to be squished into a very tight, constricting cuticle that is foreshortened and rather bulging (Zimmerman and Padgett, 2000).

Earlier workers had found similar spontaneous mutants in C. briggsae (the “micro” mutant of Nigon and Dougherty, 1950) and in C. elegans (the “dwarf” race of Dion and Brun, 1971), and after mutagenesis in C. elegans (the “pygmy” race of Nigon and Dougherty, 1954 which may have been lost).

Smooth endoplasmic reticulum

Smooth ER

A subdivision of the endoplasmic reticulum (ER) that is prominent in certain cell types in C. elegans, including muscle, neurons, and intestine, but is reduced or absent in others (Rolls et al., 2002).

See Rough endoplasmic reticulum

Smooth muscle Nonstriated muscle (S)

A muscle cell in which the endpoints of thin and thick filaments are not highly ordered, and do not show periodic striations as in striated muscles. In smooth muscles, some thin filaments are perhaps not well anchored to dense bodies or hemidesmosomes on the plasma membrane, but float freely among the thick filaments to produce thinner wispy muscle elements rather than well defined sarcomeres. Smooth muscles are common in certain locales within the nematode where they act to squeeze diffusely over valves or strictures in the digestive system and reproductive system.

See Striated muscle

Smooth septate junction  

See Continuous junction

Snout Nose (S)

The anterior end of the head, including the lips and buccal opening and the related anterior sensilla.

Social feeding

Aggregation behavior (S)
Solitary feeding (A)

A distinctive behavior in which individual nematodes choose to move together into large groups to feed together, rather than separately. In C. elegans, the behavior seems to be under the influence of an external pheromone that is received by several amphid neurons (De Bono et al., 2002) and of a second internal chemical signal, acting via the pseudocoelom and received by a separate set of sensory neurons (Coates and De Bono, 2002). When animals choose to feed separately from their neighbors, this is called “solitary feeding”. Some wild strains of C. elegans show social feeding, including the Hawaiian strain CB4856.

See Bordering
See Pheromone

Socket cell Cap cell (S)
Supporting cell (S)
Escort cell (archaic)

An interfacial epithelial cell which forms a distal cap on a sheath cell to bind the sheath of a sensillum to the neighboring hypodermis, via adherens junctions. There is often a narrow opening through the socket from the exterior into the sheath channel, allowing ciliated dendrites to be exposed to the external environment. The socket cell functions similarly to a glial cell.

In some cases the socket cell function is provided by a hypodermal blast cell, but the function segregates to a socket cell during later larval and adult stages after birth of the socket cell proper. In some sensilla (such as the phasmid) which have multiple socket cells, one socket forms the sensillar opening, while the extra socket cell(s) form wrapping processes along the side of the sheath cell ending. For some sensilla the sheath cell can also serve socket cell functions (for instance the structural cell of the sensory rays of the male tail).

See Glial cell
See Glia table
See Sheath cell
See Structural cell

Solitary feeding


See Social feeding


Cell body (S)
Perikaryon (S)

Greek derived word meaning "body" it refers to the bulbous portion of a neuron that contains the cell nucleus as well as other cellular organelles.

Somatic blastomere S1

See AB blastomere

Somatic gonad  

The components of the gonad that are separate from the germline proper. These include five tissues which are all derived from the somatic primordium: the distal tip cells, the gonadal sheath, the spermatheca, the spermatheca-uterine valve (sp-ut) and the uterus.

See Somatic primordium
See Distal tip cell
See Gonad sheath
See Spermatheca
See Spermatheca-uterine valve
See Uterus

Somatic lineage  

The pattern of cell divisions stemming from the one cell fertilized embryo is highly stereotyped in C. elegans. The cell divisions which produce the cells other than the gametes (germ cells) are called the “somatic lineage” are highly reproducible. The latter cells derive from the “germline lineage”, which does not follow a reproducible pattern.

Somatic primordium  

The set of precursor cells that later give rise to the somatic tissues of the gonadal tract. This lineage is comprised of ten cells descended from Z1 and Z4 that reorganize spatially in the L2 larva during a lull in mitotic divisions of the somatic gonad (Kimble and Hirsch, 1979). Final lineage patterns, among four of these ten cells, depend upon a signaling event within the primordium in which one of two cells adopts an anchor cell fate, while the other becomes a stem cell (Pepper et al, 2003). The two alternate lineage patterns are termed “5L” and “5R”, where Z4.aaa or Z1.ppp, respectively, adopt the anchor cell fate, yielding a total of five somatic cells on one side and four cells on the opposite side.

Somatic sheath Gonad sheath (S)
Ovarian sheath (S)
A thin cellular layer which overlies a portion of developing germline tissue. Intercellular interactions between the germline and these overlying somatic cells promote germline development (Greenstein, 2005).
Somatic tissue  

Any tissue forming the body of an organism. This excludes the germline.

Sorting endosome  

The initial recipient of material that is internalized by clathrin-dependent and independent endocytosis.

See Endosome
See Recycling endosome

Special membrane structure  

See Membranous organelle

Special vesicle  

A specialized extension of the Golgi complex on the cis face, seen in the germline (Wolf et al., 1978), where an extension of ER membrane passes through a tight cytoplasmic “collar” to form smaller vesicles on the cis face. The special vesicle may act to shuttle material to the fibrous body, where a very similar fibrous collar organizes the connection of the vesicle to the outer leaflet of the plasma membrane surrounding the fibrous body and form “finger-like projections” (Wolf et al., 1978). Still later, the special vesicle is possibly involved in the dissolution of the fibrous body and the creation of the membranous organelle in the late spermatid.

See Collar
See Finger-like projections
See Membranous organelle


An important cytoskeletal protein which forms a meshwork on the cytoplasmic surface of the plasma membrane, likely functioning to provide structure and reduce flexibility of the lipid bilayer. Spectrin networks give strength to the plasma membrane in all cells, and are essential for the integrity of neuronal processes during body motion (Hammarlund et al., 2007). Spectrin is a tetramer and is composed of two α and two β chains; each β chain has an actin binding domain at its amino terminus. The spectrin meshwork is linked to actin filaments within the cell cortex and they jointly act to control the formation of filopodia, lamellipodia, and the extension of cell processes. These are especially significant in migrating cells and neuronal growth cones. Spectrin is encoded by the sma-1 gene in C. elegans.

Sperm Spermatozoon/ Spermatozoa (S)

The mature male gamete, which merges with an oocyte to create a fertilized embryo inside the uterus. Sperm are produced from primordial germ cells during embryonic development of the hermaphrodite gonad and stored in the spermatheca. They are also produced in the mature gonad of the male animal and there are stored in the vas deferens and seminal vesicle prior to ejaculation during mating.

See Spermatozoon

Sperm aster  

A specialized form of nuclear aster that participates in forming the meiotic spindle in the early one-cell embryo (Srayko et al., 2000). The sperm aster also interacts with the actin cortex of the one-cell embryo to establish the orientation of the A/P axis (Lyczak et al., 2002).

Sperm competition  

The action of the sperm from multiple sexual partners competing to fertilize the oocyte. Since in C. elegans the hermaphrodite also produces her own sperm internallyl, sperm competition also refers to the relative success of internally derived sperm compared to sperm derived from male matings. Male-derived sperm are larger and more motile than hermaphrodite-derived sperm and thus are more successful, predominating over sperm derived from the hermaphrodite such that nearly all the oocytes are fertilized by the male-derived sperm (Ward and Carrel, 1979; LaMunyon and Ward, 1995, 1998, 1999; Singson et al., 1999).

See Sperm precedence

Sperm defective  

A category of mutations in which the animal (hermaphrodite or male) produces defective sperm and/or no sperm, and therefore becomes infertile or displays reduced fertility. The fertility of a “sperm defective” hermaphrodite can often be rescued by mating with a normal male.

Sperm expulsion  

A feature observed in post-copulatory hermaphrodites in which contractions of the uterine sheath cause sperm to leak out from the vulva. This behavior is thought to be associated with mating resistance by the hermaphrodite (Kleeman, 2005).

Sperm motility  

The ability of spermatozoa to move actively when released from the vas deferens (of the male) or from the spermatheca (of the hermaphrodite). Unlike most sperm which move via the action of a flagellum, nematode sperm crawl with a pseudopod where membrane cycles from the tip to the base resulting in a "treadmilling" of the plasma membrane. Motility has been shown to vary with the absolute size of the spermatozoon with larger sperm having an increased fitness in mating competitions within the hermaphrodite gonadal tract (LaMunyon and Ward, 1994, 1995, 1998, 1999).

See Pseudopod
See Sperm competition

Sperm precedence  

The tendency of sperm from one particular parent to predominate in their success in fertilizing the oocytes of a hermaphrodite (or female). Male sperm tend to show strong precedence over sperm derived from the hermaphrodite, thought to be due in part to the larger size of male sperm (LaMunyon and Ward, 1999). When a hermaphrodite is mated with several males, sperm precedence can refer to the success rate of sperm from one male to predominate over sperm from others. First-male precedence indicates that the sperm from the first male to mate with the hermaphrodite lead to the most progeny while second-male precedence refers to cases where sperm from the second male lead to more progeny (LaMunyon and Ward, 1998).

See Sperm competition
See Copulatory plug

Sperm transfer  

A step in the process of male mating, during which the male ejaculates mature sperm from his vas deferens into the vulva and then into the uterus of the hermaphrodite reproductive tract. This process has several steps including the initiation of sperm transfer, the release and continued transfer of sperm and the cessation of sperm transfer (Schindelman et al., 2006). After transfer to the hermaphrodite, the sperm migrate through the uterus to the spermatheca.

Spermatheca/ Spermathecae  

A somatic gonad structure (found only in the hermaphrodite) that connects the distal gonad arm to the uterus. It is composed of 24 cells that form a tube-like structure and acts as a reservoir for maturing spermatids and adult sperm which wait for an opportunity to fertilize a passing oocyte.

See Spermathecal lumen

Spermathecal lumen  

The central passage bounded by the 24 epithelial cells of the spermatheca, through which germ cells pass between the gonad arm and the uterus. The width of the lumen is usually very narrow, but as the basal surface has many longitudinal folds, it can undergo radial expansion to accommodate passage of a primary oocyte. Circumferential dilation of the distal spermatheca during ovulation is triggered by activation of the TRK pathway by the maturing primary oocyte (Clandinin et al., 1998; McCarter et al., 1999; Bui and Sternberg, 2002).

See Spermatheca

Spermatheca uterine valve

Spermathecal uterine junction (S)
sp-ut valve (S)
sujn (S)

A set of four cells (sujn) which act to restrict mature gametes from passing from the spermatheca to the uterus or vice versa. Prior to adulthood, the valve is completely blocked by the presence of two core cells (sujc) in the valve lumen. These are expelled at the beginning of egg-laying to permit the passage of oocytes through the spermatheca and into the uterus. Opening of the valve also permits the passage of sperm acquired from mating with males into the spermatheca, where they will compete with hermaphrodite-derived sperm to fertilize these oocytes.

See sujc cell
See sujn cell


The secondary spermatocytes undergo a second meiotic division to form four haploid spermatids. Initially they are connected via a central structure called the residual body, but once they have rid themselves of unneeded biosynthetic materials, they detach and are then stored within the spermatheca (in the hermaphrodite) or in the seminal vesicle (in the male). Eventually a spermatid matures, via spermiogenesis, into a spermatozoon, either within the gonadal tract or after ejaculation.

See Residual body
See Spermatocyte
See Spermatozoon


There are two different forms of this cell, the primary spermatocyte (diploid) and the secondary spermatocyte (haploid). The primary spermatocyte forms in the male gonad when a spermatogonial stem cell buds off from the rachis to form a single cell that quickly enters metaphase I and divides to form secondary spermatocytes attached to a residual body. Secondary spermatocytes undergo a second meiotic division to complete meiosis, at which time the daughter cells detach from the residual body to become spermatids. The L4 hermaphrodite gonad contains essentially similar primary and secondary spermatocytes prior to switching to produce oocytes during adult life.

See Primary spermatocyte
See Secondary spermatocyte
See Spermatid
See Spermatogenesis


The process by which immature germ cells develop within the gonad from spermatogonial stem cells into spermatocytes, spermatids, and then mature spermatozoa (for more detail see L'Hernault, 2006).

See Spermiogenesis

Spermatogenesis defective  

A class of genetic mutants in which the affected adults produce defective sperm, and are therefore infertile (for more detail see L'Hernault, 2006).

Spermatogonial stem cells  

Mitotically active diploid germ cells which are connected together via a central canal known as the rachis. They proliferate in the neighborhood of the distal tip cell of the proximal gonad, beginning in the early L4 stage and continuing to divide until late L4 stage (in the hermaphrodite) or throughout the fertile lifespan (in the male gonad). When these cells detach from the rachis they each become a primary spermatocyte.

See Rachis

Spermatogonial testis  

The distal region of the male gonad where the mitotic germline cells lie beneath a basal lamina, some in direct contact with two distal tip cells. This can be considered the distal testis, while the proximal testis is called the seminal vesicle.

Spermatozoon/ Spermatozoa/ Sperm  

The fully mature male germ cell. It is haploid and fertilizes a haploid oocyte in order to produce a diploid embryo. In the nematode, the spermatozoon has no flagellum, but moves by amoeboid motion led by a pseudopod. It contains a condensed nucleus, tightly packed mitochondria and several distinctive membranous organelles.

See Pseudopod

Spermiogenesis Sperm cell differentiation (S)

The final steps of sperm maturation where it forms its pseudopod, acquires the ability to crawl and becomes competent to fertilize an oocyte. In hermaphrodites, this stage begins when the spermatids arrive in the spermatheca. In males, mating triggers spermiogenesis. This is a quick process (about 5 minutes) and does not require any new gene expression or protein synthesis.

See Spermatid
See Spermatozoon


Archaic term for dense-staining inclusions in the intestine that are non-birefringent.

See Gut granule
See Rhabditin

Sphincter cell  

See Sphincter muscle

Sphincter muscle  

Several smooth muscle cells may act as sphincters for different organs, including the anal sphincter cell (mu sph), the spermathecal uterine valve (sujn), and possibly the control of the vas deferens and the m8 muscle of the pharynx.

See Anal sphincter muscle
See m8 muscle cell
See sujn

Sphincter valve Rectal valve (S)

See Rectal valve

Spicular pouch  

Archaic term

See Gubernaculum


Two elongated sclerotized structures in the male tail which are actively everted during copulation to fasten the male copulatory fan to the hermaphrodite vulva. They consist of a long narrow tissue extension covered by a hardened layer of cuticle and are housed within bilateral spicule channels. The spicules are controlled by specialized muscles and contain specialized sensilla. Internal spicule tissue includes process extensions from neurons, socket and sheath cells and a thin hypodermal covering, similar to the rays. In some species of nematode (not C. elegans), the spicules open at the tip via a pore to allow the internal sensory cilia to be exposed to the exterior (Clark and Shepherd, 1977).

Spicule channel Spicule pouch (archaic)

A long narrow cuticle lined canal which indents into the gubernaculum in the male tail. The canal is formed by the spicule sheath cells and opens to the exterior. The two spicules are housed within these two parallel canals when at rest, but can be extended out of the canals by action of the spicule protractor and gubernaculum evertor muscles.

See Amphid channel
See Gubernaculum

Spicule insertion  

A step in mating behavior in which the male inserts his spicules into the vulva of the hermaphrodite in order to secure a firm grip on her prior to sperm ejaculation. Spicules are pushed outward from the spicule channels by the action of the spicule protractor muscles of the male tail.

Spicule muscles  

The spicules are associated with three sets of muscles.

See Anal depressor muscle
See Protractor muscle
See Retractor muscle

Spicule withdrawal  

A late step in male mating in which the male retracts his spicules, releasing his grasp on the vulva of the hermaphrodite. Spicules are pulled back into the spicule channels by action of the spicule retractor muscles.

See Male mating behavior
See Spicule
See Spicule channel

Spike cell Tail spike (S) ABplppppppa

Two short-lived hypodermal cells in the early embryo which fuse to form a syncytium by the tadpole stage.Thse cells undergo programmed cell death during late embryogenesis at which time they leave behind a narrow spike of cuticle, often called the tail spike (Sulston et al., 1983).

See Tail spike

Spindle Mitotic spindle (S)

Most often refers to the mitotic or meiotic spindle formed by microtubules for properly alignment and separation of the chromosomes during nuclear division.

Alternately, the same term has been used in older nematode literature to refer to the contractile filament lattice of the muscle sarcomere (Bird and Bird, 1971, 1991).

Spindle force  

The balance of forces, derived from opposing forces produced by many microtubule-based motors operating along the astral microtubules, which collectively pull upon and give shape to the mitotic spindle.

Spindle orientation  

Proper orientation of the spindle is critical during the early divisions of the embryo (one cell, two to six cell) as rotation of the spindle aids results in asymmetric cell division and establishes the principal axes of the nematode body plan (Gönczy and Rose, 2006).


A term sometimes used to refer to a local synaptic branch of a neuron. Such structures can be very prominent in larger nematodes such as Ascaris (Rosenbluth, 1965). In C. elegans the term is rarely used, as most synapses occur en passant, and synaptic branches tend to be small and rather inconspicuous.

Spinneret   A type of caudal gland common in aquatic and marine nematodes whose function is to secrete material from the extreme tail tip that acts to cement the worm to the substrate. A valve-like structure may control secretory output (Lippens, 1974). No structure of this type is found in C. elegans.


A large, multi-component ribonucleoprotein complex which performs the two transesterification reaction steps of pre-mRNA splicing (see Zahler, 2005 for more details).

Spontaneous male  

Male progeny are generated by two mechanisms in the nematode:

1) During sexual reproduction according to the distribution of X chromosomes among progeny. When an XX hermaphrodite mates with an XO male, half of the progeny will receive a nullo-X sperm producing an XO karyotype and become males.

2) The self-progeny of hermaphrodites can also become male by the “spontaneous” loss of one X chromosome during meiosis in the germline. These males are identical to males produced from sexual reproduction in development and behavior and can only reproduce by sexual interaction with another hermaphrodite. Spontaneous males occur at a rate of 1/700 to 1/2000 in wild type C. elegans (Bergerac vs Bristol strains) but are more frequent in him mutant strains in which segregation of the X chromosome is disturbed (Nigon, 1949; Hodgkin et al., 1979; Hodgkin, 1980).

See Male stock
See Nullo-X sperm


A behavior seen in adult hermaphrodites, in which they rapidly move forward when touched by the tail of a male animal, evading copulation (Barker, 1994, Kleemann and Emmons, 2005).


A form of muscle arm, reaching into nerve ring from the muscle plate.

Squat phenotype  

A body morphology defect resulting from defects in the cuticle collagen genes. These animals often have a rolling phenotype and can be dumpy as well.


See Sarcoplasmic reticulum

SS cells  

Primordial stem cells of the somatic gonad that are fated to produce sheath and spermathecal lineages; these include Z1.ap, Z1.paa, Z4.app and Z4.pa.

Stack/ Stacking  

A set of seven organized syncytial epithelial toroids (A-F), or rings, which line the vulval entryway sequentially form a narrow tube that has been called the stack, since each ring of cells sits atop neighboring rings above and below (Podbilewicz, 2000). The process by which the epithelial cell group migrate to surround the vulval channel has been called “stacking”.

See Ring cell
See Toroidal cells
See Vulva

Stacked membrane  

Different types of membranes form parallel stacks in different orientations.

1) In the plasma membrane, specialized secretion units consist of parallel infoldings that form uniformly spaced stacks that enclose specialized extracellular spaces that may be essential for secretion of elongated molecules, such as collagen, for the cuticle. 

2) The cytoplasmic membranes of the Golgi apparatus can form stacks of closely apposed balloons of membrane which enclose specialized environments involved in segregation and maturation of secreted proteins prior to their shipment to the plasma membrane. 

3) The membranes of the endoplasmic reticulum can become closely stacked in parallel within the cytoplasm.

4) Inside the mitochondrion, short membrane elements can be closely apposed to form “cristae”.

See Cristae
See Endoplasmic reticulum
See Golgi
See Secretory stack


Methodology for evaluating a particular developmental time point, or “stage”. A wide variety of physical attributes have been used to characterize these time points, from time of egg-laying, time of hatching, time of molting, time of the onset of egg-laying, or discrete moments in development (particular cell divisions, appearance of a distinctive tissue structure). Some methods involve selecting single animals when that appearance is noted, other methods involve synchronizing masses of animals according to re-feeding a starved population, selecting “hatchees” or new eggs in a time window.

See Egg plate
See Hatch-off
See Lay-off


The anterior portion of pharynx, including the posterior buccal capsule (surrounded by the pharyngeal epithelium), the flaps, and the portions surrounded by pm1 and pm2 muscles (Dolinski et al., 1998; Dolinski and Baldwin, 2003).

Stem cell Blast cell (S)

In higher animals this term usually refers to a cell that remains undifferentiated into juvenile or adult life and which is still capable of further (unlimited) cell divisions to later produce a variety of different cell types (perhaps being totipotent).

In the C. elegans gonad, the undifferentiated cells in the distal gonad (mitotic zone) fit this definition best. Although their immediate daughters only go on to become spermatocytes or oocytes or to undergo programmed cell death, their distant progeny (after mating) are totipotent. They can undergo many divisions and are nearly immortal.

Among C. elegans somatic cells, the term is most often used to refer to (differentiated) cells that are capable of undergoing repeated cell divisions to produce new daughter cells of various types, while at each division, one daughter retains the initial cell fate. Examples include the seam cells, which can repeatedly divide while one daughter retains the seam cell fate after each division. These cells are not truly totipotent, but produce a limited, predictable set of daughters, and unlike in higher animals, these cells have a differentiated phenotype themselves. The P ventral neuroblasts are another example since they also display a stem cell-like division pattern and they remain undifferentiated into larval life at which point they undergo a fixed number of divisions to produce a limited range of progeny.

See Blast cell
See Seam cell   

Stem cell pattern Asymmetric lineage pattern (S)
Asymmetric cell division (S)

A pattern of cell divisions where the precursor cell produces two daughter cells of unequal shape and/or size, which usually go on to adopt different cell fates. Such divisions often occur across the anterior/posterior plane, or the dorsal/ventral plane. These are very common in most C. elegans lineages.

See Symmetrical cell division

Sterile Infertile (S)
Fertile (A)
Gravid (A)

Incapable of producing new progeny or new fertile gametes.

See Infertile
See Gravid
See Post-reproductive

Stoma Buccal cavity (S)

The most anterior region of the digestive tract, anterior to the pharynx.  It is comprised of three subregions, the cheilostom, prostom, and telostom


See Stomodeum

Stomatointestinal muscle  

Formed from two cells, this is the only muscle associated with the intestine and is located at its posterior end. Its myofilaments run principally longitudinally, and their attachments are diffuse: medially to the intestine (smooth muscle-like) and peripherally to several points along the bodywall, dorsal, ventral and lateral (single sarcomere-like). Contraction of these muscles pressurizes the intestinal contents near the posterior end of the intestine, thus promoting defecation. They contract simultaneously with the anal depressor and anal sphincter muscles during the EMC step of the defecation motor program.


A form of hollow stylet found in some parasitic nematodes, used for sucking fluids from the host plant or animal prey. It is often protusible from out of the mouth, controlled by stylet muscles, and may be formed by keratinized buccal cuticle.

See Odontostyle
See Stylet

Stomatous Astomatous (A)

Having a mouth or mouth-like opening.

See Stomodeum


Stomodaeum (S)
Stomatodeum (S)

Refers collectively to the pharynx and buccal cavity, the most anterior portions of the alimentary system. The lips and buccal opening (mouth) may also be considered as part of the stomodeum.

Stress fiber  

A very broad aggregation of parallel sets of intermediate filaments, anchored to the plasma membrane of a cell to provide strength to the cell shape. They are common in epithelia that are normally under severe mechanical stress.

See Intermediate filament

Stretch receptor Stretch activated channel (S)
Stretch sensitive channel (S)

Postulated function of long undifferentiated neurites along the longitudinal nerves, especially those extended processes of motoneurons that have no regional involvement in synapses. They have been postulated to coordinate local motor neuron activity in order to create a smooth sinusoidal body motion (Neibur and Erdos, 1991).

A stretch receptor neuron that regulates sensory-motor integration during locomotion was identified after characterization of the C. elegans homologue to the mechanosensitive TRPN channel, trp-4, revealed that it acts in a single neuron, DVA, to mediate its function. (Li et al., 2006).

See Sinusoidal wave
See Locomotion

Striated muscle

Somatic muscle (S)
Obliquely striated muscle (S)
Non striated muscle (A)
Smooth muscle (A)
Single sarcomere muscle (A)

A multiple sarcomere muscle cell in which the thin and thick filaments adopt highly ordered patterns, with the thin filaments anchored at dense bodies. In C. elegans, there are 95 body wall muscles that have this obliquely striated pattern, with several sarcomeres (motor units) lying next to one another in an orderly array, running at a slight angle to the body axis. This organization produces periodic striations and filament banding patterns, such as the M-line, Z-band, and A-band. More specialized muscles in C. elegans typically consist of single well-ordered sarcomeres, in which the thin filaments are again highly ordered and anchored to well defined dense body structures, but these “single sarcomere” muscle cells are included in the non-striated class. Obliquely striated muscles are common across many nematode species (Rosenbluth, 1965).

See Muscle
See Obliquely striated
See Thick filament
See Thin filament

Striated rootlet Ciliary rootlet (S)

A filamentous specialization within some types of sensory dendrite (eg. cephalic sensillum, inner labial sensillum, male ray), usually extending proximally from the basal body, perhaps consisting of microtubules or intermediate filaments, which shows parallel striations when viewed in lengthwise section along the dendrite. They can vary in length from less than 1 micron to 4-8 microns or more.

Structural cell


Support cell (S)
Structural element (S)

In male sensory rays, a structural cell provides the combined duties of both a sheath cell and socket cell. The distal process of the structural cell is enlarged to form a protective surrounding for the ciliated endings of the two ray neurons, forms a narrow opening to the exterior environment, and is tightly sealed to the overlying hypodermis within the tail fan cuticle by adherens junctions. By analogy one could use this term to refer collectively to the sheath cells or socket cells of other sensilla.


A thick, electron dense connecting element between outer layers in the adult cuticle.

Stutter turn  

See Turning

Stylet Stomatostylet (S) Odontostylet (S)

A specialized form of feeding structure (a specialization of the buccal cavity and cuticle) in some parasitic species of nematodes, but not found in C. elegans, adapted particularly for the food of choice, such as to attach to a plant stem. In some species, the stylet may be extensible or retractable, and these structures can vary widely in form.

See Odontostyle
See Stomatostyle


This term has had multiple conflicting usages:

1) Used (conventionally) as a synonym for hypodermis (Bonner et al., 1970; Lewbart, 2006).

2) Used (uniquely) to define a region between, or spanning, the basal cuticle and the hypodermal membrane, thus being neither cuticle nor hypodermis per se (Perkins et al., 1987).

3) Used (oddly) to define a layer of the cuticle, perhaps equivalent to an outer basal lamina just under the basal cuticle (DeGrisse and Roman, 1974; DeCraemer et al., 2003).

See Basal zone
Sublateral nerve cord Sublateral cord (S)
Submedian nerve cord (S)

A set of four minor longitudinal nerve cords that run most of the length of the body beneath each muscle quadrant (subdorsal or subventral positions), or more posteriorly, just lateral to the muscle quadrant in sublateral positions. These nerves form cryptic synapses onto the bodywall muscles of unknown function (Hall, Rand and Duerr, unpublished).


A characteristic pattern of cell divisions that occurs in many different lineages, usually in order to produce homologous cell groups. Such a pattern is found in the lineage of the male rays.


A proposed mode of cell death in which a decision is made within the cell nucleus to initiate a series of cellular changes in both the nucleoplasm and cytoplasm resulting in eventual death of the cell by apoptosis (Hedgecock et al., 1983; Conradt and Xue, 2005).

The same term might be applied to a whole animal that wanders off of a culture plate in search of different environmental conditions, although it is assumed that such animals are seeking better conditions, and not the termination of their life.

See Apoptosis
See Murder
See Necrosis

sujc cell Spermathecal uterine core cell (S)
Core cell (S)

This binucleate cell forms an early plug which blocks passage through the sujn valve during morphogenesis. Each core cell is presumably displaced and/or undergoes apoptosis prior to the passage of the first germ cells through the spermatheca. The core cells derive as granddaughters of r cells in the uterine lineages.

See Spermatheca uterine valve
See sujn cell

sujn cell Spermathecal uterine junction cell (S)
Spermathecal valve (S)

The valve cells likely act as a sphincter muscle, consisting of four fused cells separating the uterus from the spermatheca; they are granddaughters of r cells in the uterine lineages

See Spermatheca uterine valve
See sujc cell

Supernumerary cell Extra cell (S)

A cell that is exists in excess of the normal number for a given structure or tissue, perhaps in response to a mutation or developmental anomaly; that is to say an “extra cell” of that category or for that position.

Supernumerary microtubules  

A class of singlet microtubules extending in the distal cilia of some sensory neurons which do not extend directly from the cylinder of microtubules forming the transition zone. They are in addition to those which comprise the axoneme itself.

Support cell Sheath cell (S)
Socket cell (S)
Structural cell (S)
Accessory cell (S)

See Neuronal support cells

Surface coat Glycocalyx (S) Envelope (S)

This term has multiple meanings:

1) It can refer to non-collagenous material lying external to the epicuticle. This material often consists of glycoproteins secreted from the sensory orifices, the pharyngeal glands, and/or the excretory system, to cover the outer vitelline membrane in a patchy fashion (for detail, see Page and Johnstone, 2007).

2) This term can refer to the glycocalyx, a set of glycoproteins covering the external surface of lumenal membranes of the various organ systems, including intestine, excretory canal, uterus and spermatheca.

3) This term could refer to the non-membranous outer covering of the young unfertilized embryo, and to the outer vitelline layer of the eggshell after fertilization.

See Glycocalyx

Swimming Thrashing (S)

Nematode body motion when placed into a liquid environment. Some species swim or move effectively in liquid, especially marine species, whereas others are poor swimmers (Nicholas, 1975). C. elegans’ motion in liquid has often been described as thrashing, since the animals generally fail to make rapid forward progress. C. elegans may swim better in liquids of thicker viscosity or in very shallow liquids, where surface tensions may contribute additional traction. The body shape during swimming seems to flex all muscles on one side almost simultaneously, unlike its sinuous body shape during crawling. When this motion starts near the head, it is termed a “forward swim” and when motion initiates near the tail it is termed a “reverse swim” (Faumont et al., 2005).

See Crawling
See Locomotion
See Thrashing

Switched response  

A mechanism for response to a stimulus that involves both klinokinesis and klinotaxis, and adaptation to the stimulus. It has been proposed that C. elegans may use this mechanism in generating its normal sinusoidal motion on a substrate (Dusenbery, 1980).

See Kinesis
See Taxis


A creature (animal, plant, or bacteria) that lives in a permanent or prolonged relationship with another. An endosymbiont lives within the tissues of the host, while an exosymbiont lives on the body surface of the host.

See Symbiosis


A living arrangement in which two animals, usually of different species, which live in close proximity with beneficial consequences for at least one member. Some nematodes are internally parasitized by Wolbachia bacteria in a relationship that seems to actually help the nematode’s fertility and growth rate (Foster et al., 2005; Taylor and Hoerauf, 2001).  

Symmetrical cell division Symmetric lineage pattern (S)

A division in which both daughter cells go on to adopt similar morphology, and parallel or identical cell fates; such divisions usually occur across transverse planes. This type of cell division is fundamentally different from the unequal cell divisions and unequal cell fates seen in “stem cell” lineages. Few lineages within C. elegans adopt symmetric cell divisions, except in the germline and a few mesodermal and endodermal lineages.

See Asymmetrical cell division
See Stem cell pattern

Synapse Chemical synapse (S)
Electrical synapse (S)
Neuromuscular junction (S)
Synaptic contact (S)

This term can refer to several different structural features:

1) A chemical synapse is a communicating intercellular structure in which a chemical neurotransmitter is released from presynaptic vesicles in a neuron process into the synaptic cleft, after which one or more postsynaptic neurons are influenced via membrane-bound receptors in their plasma membranes adjacent to the cleft. A neuromuscular junction is a specialized form of chemical synapse involving a presynaptic motor axon and one or more postsynaptic muscle elements. In C. elegans synapses, there is little or no visible specialization of the postsynaptic membrane, but the presynaptic terminal always features a presynaptic density and a cluster of vesicles. In C. elegans most are en passant structures, not involving a terminal branch for either the presynaptic or postsynaptic members.

2) An electrical synapse is a communicating intercellular structure, often referred to as a gap junction, in which the plasma membranes of two adjoining cells are held in close proximity by a cluster of intramembrane proteins in each membrane that fuse on their extracellular faces to create a series of narrow patent intercellular channels. Such gap junctions occur commonly between neurons, but in C. elegans they are also common between many types of epithelia, and between muscle arms.

3) Archaically, this term sometimes was used to refer to a place of joining of two elements, what is now more properly called a “synapsis”.

See Dyadic synapse
See Monadic synapse
See Triadic synapse
See Reciprocal synapse

Synapsis Pairing (S)

An event during meiotic prophase during which homologous chromosomes form linear pairs or “bivalents”, closely bound (synapsed) along their length, so that corresponding segments of each chromosome are paired to that portion of their neighbor.

See Synaptonemal Complex

Synaptic cleft Cleft (S)

The extracellular space lying immediately under the active zone at a chemical synapse. While; the space immediately between the pre-synaptic and post-synaptic membranes at a chemical synapse is often widened in higher animals, in C. elegans the space remains quite narrow and not so distinctively organized.

Synaptic density Presynaptic density (S)

A small electron dense bar lying in the cytoplasm against the plasma membrane of a presynaptic neuron, around which are clustered the synaptic vesicles at a chemical synapse.

Synaptic plasticity  

A change in relative strength of a synaptic connection in time, either due to progressive neural development, or in relation to ongoing activity patterns of the synapse. Such changes can include simple forms, such as habituation or sensitization, or complex ones associated with learning and memory.

Synaptic terminal  

Pre-synaptic and postsynaptic

Synaptic transmission Neurotransmitter release (S)

Refers to the process of information transfer between two neurons; usually in reference to chemical synapses, but can also be used to refer to electrical synapses (Richmond, 2005).

Synaptic vesicle  

A small membrane-bound organelle, filled with neurotransmitter(s) and/or neuropeptides, which occur in clusters at presynaptic sites in neuronal processes. They vary in size from 30-50 nm in diameter, and their constituents may originate from somewhat larger transport vesicles produced in the neuron soma (Hall and Hedgecock, 1991). Synaptic vesicles release their contents into the synaptic cleft by vesicle fusion (exocytosis) with the presynaptic membrane, at sites immediately adjacent to the presynaptic density, as the key aspect of neurotransmission (Richmond, 2005). Afterwards their vesicle membrane may immediately re-form an empty vesicle (“kiss and run” synaptic transmission) or the membrane may fuse fully into the plasma membrane and later be reformed at the periactive zone to form an empty vesicle by endocytosis.

Synaptic vesicle cycle  

An endocytic cycle that recycles synaptic vesicles. Vesicles loaded with transmitter are mobilized to the plasma membrane where they dock, prime and become fusion competent. Upon a rise in calcium levels, neurotransmitter is released and the vesicle is translocated and recycled via clathrin-mediated endocytosis (Richmond, 2005).

See Endocytosis

Synaptonemal complex  

A distinctive layered structure, with a zipper-like appearance, which binds two condensed chromosomes together during the pachytene stage of the cell cycle. An array of protein modules hold the homologous chromosomes in co-alignment; these protein modules comprise the “zipper” and are the basis of the synaptonemal complex. The complex remains intact until later in meiotic prophase before disassembly, and its appearance is considered a hallmark of this stage in meiosis (Colaiacovo et al., 2003).

Synchronous culture Synchronized worms (S)
Synchronized plates (S)
Synchronous population (S)

A culture of animals manipulated to so that all surviving members of the population are in the same narrow range of developmental stages.This can be accomplished by various techniques, including selective killing of all other stages (by detergent or bleach treatment, for instance), or by the collection of simultaneous newly hatched animals from an “egg plate”, or by beginning with starved young larvae and placing them on new food all together.

See Egg plate
See Hatch-off
See Lay-off

Syncytium/ Syncytial  

Several cell types in C. elegans commonly fuse their plasma membranes to form syncytial compartments of 2-50 or more cells. This is especially common in hypodermal tissues, among the pharyngeal muscle cells, some gland cells and in the vulval toroids as well as some other reproductive structures such as the spermathecal-uterine valve (sujn). In addition, the germline forms a syncytium via linkages to a central rachis. Some cell processes (of neurons or glands) fuse distally to form a single larger process “axon ring” or a process which forms a complete ring around another object, as in the nerve ring or pharynx.

The early scientific literature on nematodes (prior to electron microscopy) identified many additional “syncytia” which have not been found in subsequent ultrastructural studies. Thus Goldschmidt (1908, 1909) incorrectly reported many fused neurons in Ascaris. The plexus of muscle arms at the motor endplates were often described as a syncytium, but are not actually fused, although they are electrically coupled (Weisblat and Russell, 1976; Johnson and Stretton, 1980).

See Axon ring
See Rachis
See Toroidal cells

Syngamy Amphimixis (S)

Fusion, as it relates to fertilization via two germ cells, egg and sperm.

sys phenotype Symmetric sisters phenotype

A genetic mutation which causes a failure of the asymmetric cell division of the Z1 and Z4 blast cells in the somatic germline such that both daughter cells (Z1.a and Z1.p, etc.) are equivalent in size and adopt the same fates, producing an AC/VU precursor but never a DTC fate. The resulting gonad fails to extend out “arms” from the developing germline, and instead produces a single central mass of germ cells near the vulva (Miskowski et al., 2001).

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 S. In WormAtlas.  doi:10.3908/wormatlas.6.19