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Glossary - E




E, E2, E4, E8, E16, E20   These descriptors are used to designate developmental stages in intestine organogenesis during which the intestinal primordium consists of the founder cell E, then 2 E daughter cells, 4 E, 8 E, 16 E and 20 E daughter cells, etc. In this intestinal cell lineage, all daughters of E blastomere become intestinal cells.
E blastomere E founder cell (S) The primordial embryonic cell that gives rise to the intestine and no other cell types.
E cell

U cell (S)
Postembryonic E ectoblast (S)

Former name (e.g. in Sulston and Horvitz, 1977) of one of the rectal epithelial cells. Later renamed as U cell. Terminally differentiated in the hermaphrodite tail, but acts as a blast cell in the male.

See U cell

e cells e1D

Pharyngeal epithelial cells.


e neuron ASE (S) See ASE cell
Early endosome  

A category of endosome likely to be involved in endocytosis and recycling of materials, but not yet well established histologically in C. elegans.

See Endosome

Eccritic temperature  

The temperature at which a group of animals tends to accumulate preferentially; it is often related to the temperature at which the animals have become previously acclimatized. C. elegans individuals can show very acute selectivity for this preferred temperature (Hedgecock and Russell, 1975).


This term encompasses both the processes of molting and exsheathment.

See Molt
See Exsheathment

Echo phenotype   A mutant phenotype where there is a repetition in the defecation motor program with a consistent latency of 10-12 seconds (Reiner et al., 1999).
Eclosion   The process of exiting from the eggshell by the young L1 larva; the last step in hatching.

Extracellular matrix (S)
Basal lamina (S)
Basement membrane(S)

See Basal lamina


A stem cell lying in the outer body wall that gives rise to epithelial cells, glia and neurons.

See Blast cell



Outermost layer of tissue in a developing embryo. This layer gives rise to the outer surface (skin) of the organism as well as the nervous system and other external organs and structures. In C. elegans, ectoderm includes the hypodermis, seam and interfacial epithelial cells and all their precursors, as well as blast cells that lie within the hypodermis such as P0-P12 until they differentiate.

See Hypodermis


Any parasite which lives on the exterior surface of its host animal or plant.

See Endoparasite
See Parasite

Ectopic   Refers to a cell or cell part that develops in excess of the normal number, or in a new location compared to the normal number or location of similar cells, or cell parts. The ectopic structure may not adopt completely mature or normal features due to its aberrant placement.
EF cells EF1/2
Large, male specific neurons with cell bodies in preanal ganglion. They receive synaptic inputs from ray neurons.

Zygote (S def.1)
Ovum (S def. 2)

1) A diploid cell produced by the union between two gametes, a sperm and an oocyte, and is surrounded by a protective outer shell (embryo).

2) A haploid reproductive cell (gamete) produced by the hermaphrodite C. elegans and develops into an embryo when fertilized by a sperm (oocyte).

Egg chamber   The expanded lumen of the uterus after passage of the first fertilized oocytes. Before maturity the uterine lumen is collapsed in C. elegans and features many inward-projecting ridges, but upon inflation the lumen becomes rigidly expanded into an open chamber which remains inflated even when empty of oocytes.
Egg laying

Ovulation (S)
Oviposition (S)

The behavioral program that serves to move fertilized eggs down the uterus, through the vulva, and out of the worm onto the substrate. Egg-laying is controlled by the function of the vulval (vm1 and vm2 type) and uterine (um1 and um2 type) muscles. The uterine muscles contract to squeeze the eggs out of the uterus while the vulval muscles contract to open the vulval orifice. Two classes of motor neurons synapse onto these muscles; the two HSN's and the six VC's. HSN's are essential for egg-laying while VC's are not, as shown by laser ablation studies. HSN's are serotonergic as well as possibly cholinergic. All VC's are cholinergic and VC4 and VC5 are also serotonergic. Serotonin and levamisole, nicotinic Ach agonists, strongly induce egg-laying. Serotonergic and cholinergic pathways are suggested to act in parallel for this function (Weinshenker and Thomas, 1997).

C. elegans modulates its rate of egg laying in response to a variety of environmental conditions; absence of food as well as high osmolarity lead to suppression of egg laying, while the volatile attractant isoamyl alcohol stimulates egg laying in the absence of food (Sawin and Horvitz, 1991).

See Egg retention
See Bag of worms

Egg plate  

A culture plate containing very many developing eggs. This may be produced by the “lay-off” method to produce semi-synchronous eggs, or by choosing a highly populous plate and gently washing off all hatched worms, leaving non-synchronized eggs behind. Synchronization can be achieved among the progeny by a “hatch-off” technique, either by picking individual eggs which have reached the desired age, or by allowing eggs to hatch over a narrow time window, and then collecting these recent hatchees by gentle washing.

See Lay-off
See Hatch-off

Egg retention  

Congestion of the adult hermaphrodite uterus with excess fertilized eggs due to a decrease in the rate of egg-laying. This may result from changes in motor activity that govern the operation of the egg-laying muscles (as in conditions reducing the amount of serotonin released from HSN neurons), or may be due to developmental changes that cause the vulva to be malformed or closed, as in the Egl or Vul mutants (Desai and Horvitz, 1989; Han et al., 1990). Egg retention also occurs in wild type animals when food is scarce.

See Egg laying


A tough protective coating that covers the developing embryo very soon after fertilization of the oocyte. Most or all may be formed by secretion from within the embryonic tissue, but an outer "oolemma" layer is reportedly secreted by the uterine sheath (Anya, 1976; Bird and Bird, 1991). The eggshell consists of an external vitelline layer, a tough central layer made principally of chitin, and an internal lipid layer. The young L1 larva emerges from the eggshell about 10 hours after fertilization. Secretions from pharyngeal glands may weaken it just prior to hatching. Careful dissection can allow the outer chitinous layer to be removed without perturbing embryogenesis (see Schierenberg and Junkersdorf, 1992). Modest sized holes in the vitelline membrane, caused by laser ablation, will reseal and still allow embryogenesis. Many sources confuse the positions of the three layers, putting the vitelline layer inside rather than outside the chitinous layer for the C. elegans eggshell.
In common usage, the term eggshell is often equated solely with the chitinous layer.

See Chitinous layer
See Lipid layer
See Oolemma
See Pellucid layer
See Vitelline layer
See Vitelline membrane
See Zona pellucida


EGg Laying mutant phenotype.
There are two types of egl phenotype: 1) egl-d or egl refers to those mutants where an animal is defective in egg laying and retains its eggs (Trent et al., 1983; Desai and Horvitz, 1989); 2) egl-c refers to those animals that constitutively lay eggs. egl-c can be detected as more immature eggs being laid by mutants than those laid by wild type (reflecting decreased uterine residency time) or as an elevated rate of egg-laying relative to wild type in the absence of food (Barnes and Hekimi, 1997).

See Bag of worms
See Matricide

Ejaculation   The behavioral process by which sperm is rapidly transferred from the male’s vas deferens into the hermaphrodite’s uterine chamber; a subprogram of male mating behavior.
Electrical synapse Gap junction (S) A channel that forms between two cells where their plasma membranes become closely apposed, and allows passage of small molecules and ions from one to the other as a way of intercellular communication. At these points, cell membranes are separated by a 1 nm “gap” when viewed anatomically. These synapses are found in the early embryo between undifferentiated blastomeres, and in virtually all cell types in the adult nematode, most often connecting functionally and/or lineally related cells, but also occurring between cells of unrelated origin. While many of these synapses operate to electrically couple the cell pair, the synapses may also allow the direct passage of metabolites or intercellular signals from the cytoplasm of one cell to the cytoplasm of its neighbor. In C. elegans and other invertebrates these synapses are formed by “innexin” proteins, whereas in vertebrates they are formed by “connexins” (Phelan and Starich, 2001).
Electron microscopy EM

There are two types of electron microscopy, scanning (SEM) and transmission (TEM). SEM images the surface of the structure or organism, while TEM occurs on thin slices of the tissue and allows for very high magnification of the specimen.

Wormimage provides a searchable database of TEM images of many different C. elegans animals while Slidable Worm provides TEM images along the length of an animal.

For detailed methods, a number of electron microscopy techniques are available.


This term can refer to many separate developmental processes, including:

Elongation of the embryo: begins soon after the end of gastrulation, and is caused by circumferential squeezing by the hypodermal cells surrounding the embryo, followed by deposition of a cuticle layer to hold the worm in this new shape (Priess and Hirsh, 1986). Time for elongation to proceed is roughly 2 hrs. This form of elongation does not depend upon new growth in embryo volume or new cell divisions, but only on the reshaping of existing cells.

Elongation of the excretory canals: grow rapidly along the bodywall from the cell body during late embryogenesis and the first larval stage. The canal is simultaneously reshaped and grows rapidly in total size, with most new growth occurring at the canal tips (Buechner, 2002).

Elongation of a neuron: directed at the axon tip by the growth cone, where new growth is focused and the axon position is redirected along specific pathways (Wadsworth et al., 1996).          


A mutational phenotype where EMBryonic development is defective mostly leading to arrest at various stages.

See Embryonic lethal
See Embryonic arrest
See Let


A stage of development of C. elegans between the time that the oocyte is fertilized and the point at which the the mature embryo emerges from the eggshell at hatching as a young L1 larva.

See Embryonic stages

Embryogenesis   The process of formation and development of the embryo (see pictures by Nomarski and SEM imaging). For detailed, muti-dimensional movies see GLOWorm Notes.
Embryonic arrest Dead egg (S)

The cessation of normal developmental steps within the embryo, most often caused by a mutation or a physical defect. Besides mutation (Denich et al., 1984), embryonic arrest can also be induced in some cases by laser ablation of certain embryonic cells, laser surgery to fuse embryonic cells (Schierenberg, 1984), destruction of the vitelline membrane (Schierenberg and Junkersdorf, 1992), removal of egg cell cytoplasm (Laufer and von Ehrenstein, 1981), and/or interference with early cell-cell interactions (Priess and Thomson, 1987). Arrest is more severe than mere developmental delay or alterations in the order of cell divisions, which are more likely to result in reasonably normal overall development and production of a functional animal at hatching (Junkersdorf ).

Embryonic arrest is seldom if ever reversible, and therefore leads to lethality. However the aberrant embryo may continue to persist for hours or even permit some cell divisions to create a developmental monster.

See Arrest stage
See Let
See Monster
See Terminal phenotype

Embryonic axis  

The longitudinal axis of the early embryo before gastrulation. The early embryo is oblong in shape, with the P granules sequestered at the posterior pole, opposite from the slightly narrower anterior pole.

Embryonic culture medium   A specific type of medium in which embryos or isolated blastomeres can be cultured (Shelton and Bowerman, 1996).
Embryonic lethal  

A mutant phenotype in which some or all embryos suffer embryonic arrest, failing to progress to the L1 stage. Individual mutant alleles may arrest at characteristic developmental timepoints within embryogenesis. There are very many different categories of mutant within this broad designation.

See Let
See Monster

Embryonic sheath  

A form of basal lamina or glycocalyx which is secreted by the unfused hypodermal cells of the early embryo. It covers the embryo before the onset of elongation and is required to spread the forces of elongation equally over the embryo’s outer surface (Priess and Hirsh, 1986). This extracellular sheath lies on the apical surface of the hypodermis and is later replaced by the early cuticle.

Emo ;

EndoMitotic Oocytes phenotype. A mutant phenotype where meiotic maturation is not followed by ovulation and the mature oocyte is trapped in the gonad arm where it endomitotically replicates its DNA (Dang et al., 1996). Somatic sheath cell and spermatheca ablation also disrupts ovulation and causes Emo phenotype (McCarter et al., 1997). Besides the enlargement of their nuclei due to endomitosis, these oocytes are also subject to tearing forces as they enter the spermatheca. As a result they may break into several pieces, one containing the nucleus, and some smaller cytoplasts, which are formed as separate structures inside the proximal arm or inside the uterus.

EMS Ethyl methane sulfonate (S) A chemical mutagen that generates point mutations (G/C-A/T transitions) and to a lesser extent small deletion and other chromosomal rearrangements (Johnsen and Baillie, 1997). EMS is routinely used in C. elegans to produce visible mutants (Anderson, 1995; Barstead and Moerman, 2006; Flibotte et al., 2010).
EMS blastomere EMSt blastomere (S)

The progenitor cell of the E and MS blastomeres. This was formerly called S2 or EMSt, since it gives rise to “somatic” tissues: Endoderm, Mesoderm and Stomodeum.

See Founder cell

En passant   The most common form of chemical synaptic contact in the nematode, in which the presynaptic axon does not form a terminal specialization, but only a local swelling in the neighborhood of the postsynaptic target axon(s).
Enclosure   This term is usually used to describe a step after gastrulation in which the C. elegans embryo becomes fully covered by a sheet of hypodermis.

Free ending (S)
Bare ending (S)

A subclass of neurite end points which are often presumed to be sensory by their unique positions; sometimes used to ascribe a sensory function where no obvious physical specialization (such as a cilium) can be visualized, or where the apparent sensory features are diffuse.

See Dendrite


The innermost layers of the cuticle.

See Basal zone


A process by which a cell actively takes up material from its external environment by inward bending of the plasma membrane to create vesicles that encapsulate this material and carry it into the cytoplasm. There are multiple mechanisms for this process, including clathrin mediated uptake, caveolae-mediated uptake and clathrin- and caveolae-independent internalization.

See Coated vesicle
See Phagocytosis
See Pinocytosis

Endoderm   Early blast cells that give rise to the gut tissue in C. elegans.

Chromosomal replication without nuclear or cellular division that results in a cell containing a highly enlarged nucleus with multiple copies (greater than 2X) of each chromosome (Rose et al., 1997). When this process occurs in the oocyte, it is called the Emo phenotype.

See Emo
See Endoreduplication


Any parasite that lives within the body of the host animal or plant.

See Ectoparasite
See Parasite

Endoplasmic reticulum


A network of branching tubules and sacs extending throughout the cytosol forming a continuous sheet. Its membranes are the site of production for transmembrane proteins and lipids. Often, import of proteins occurs before the polypeptide is fully formed (co-translational). The ribosomes that synthesis the protein coat the surface of the ER creating regions called rough ER (regions without ribosomes are termed smooth ER).

See Rough endoplasmic reticulum
See Smooth endoplasmic reticulum

Endoreduplication Endomitosis (S)

Multiple rounds of DNA replication that take place without chromosome condensation, segregation or cytokinesis. Endoreduplication results in enlarged, highly polyploid cells. This process is normally seen in intestinal nuclei during each larval lethargus which results in adult intestinal nuclei with 32 copies (32C) of each chromosome (Hedgecock and White, 1985). It is also seen in adult wild type hypodermal nuclei.

See Endomitosis

Endosome   A membrane-bound organelle that forms following endocytosis. The properties of endosomes are still not well described for C. elegans cells due to incomplete histochemical studies, though the multivesicular body is easily identified just by its anatomy in nematode tissues.
Engulfment   Process by which a cell or tissue becomes surrounded by a neighboring cell and phagocytosed. In some cases engulfment is clearly subsequent to an apoptotic event or a necrotic event within the engulfed cell, while in other cases the engulfment may precede or be coincident with the cell death.

See Phagocytosis

A nematode that retains two full layers of cuticle and hence gains extra protection against the exterior environment. This condition is not normally observed in C. elegans, but is common in some other nematode species.

See Molt

Entomopathogenic nematodes  

Soil dwelling nematodes that infect insects, including the larval stages of butterflies, moths, beetles and flies as well as adult crickets and grasshoppers.


A process at the end of gastrulation by which some cells migrate forward to cover the blastopore, covering the hole through which previous cells had entered inside the gastrula (Chisholm and Hardin, 2005).


Cortical layer (S)

External cortical envelope (S)

The outermost collagenous layer of the cuticle, which appears densely staining by electron microscopy, and may consist of a multi-layered membrane. It is underlain by successive collagenous cuticle layers, and is often coated on the outside by a noncollagenous matrix called the surface coat, or glycocalyx. The epicuticle can be considered the outermost portion of the cuticle’s “cortical zone” (Bird and Bird, 1991).

See Cortical layer

Epidermal gland   A characteristic specialization found along the lateral hypodermis in some nematode species, but not found in C. elegans. Each consists of a single modified hypodermal cell that secretes granules into a local duct or pore in the lateral cuticle. Some glands also include one or more neurons that extend sensory endings into the duct, or into the gland cell itself (Bird and Bird, 1991). They may secrete material for the surface coat of the cuticle.
Epidermis Hypodermis (S)

Hypodermis of C. elegans. These two terms refer to the same tissue and are used interchangeably in publications (Chin-Sang and Chisholm, 2000).

See Hypodermis
See Ectoderm


A blast cell that can give rise to epidermal cells, glia and neurons in C. elegans.

See Blast cell

Epistasis   An interaction between two different genes, such that the effect of an allele of one gene is suppressed or masked by the effect of an allele of a second gene.
Epithelium   The layer of cells that cover the external surface of an organism as well as forming an inner lining between the tissues and organs of that organism and the external environment. In C. elegans epithelial cells include epithelium of the alimentary tract, intestinal cells, hypodermis, interfacial cells and somatic gonad cells.
Equivalence group   A set of cells that all have the (equal) potential to proceed in forming a specific structure, or whose progeny each have the potential to adopt various roles in that structure, as in the development of the vulva and the male sensory rays (Sulston and White, 1980; Sommer, 2005).
Erector muscle Gubernacular erector (S) One of the specialized muscles of the adult male tail, which operates to change the shape of the gubernaculum during male mating behavior.
Escort cell Socket or sheath cell of amphid (S)

Archaic (Golschmidt, 1903; Mclaren, 1976)

Esophageal gland  

Pharyngeal gland

See Gland cell

Esophagus Pharynx (S)

Archaic term for the pharynx.
(Alternate spelling=Oesophagus)

Eutelic/Eutely   A property of some invertebrate animals, including C. elegans, of having a fixed number of somatic cells in the adult body. This number is specific for each species. In C. elegans, these cells derive from a fixed lineage where virtually all cells have final fates determined by their position in the lineage (Sulston and Horvitz, 1977).

A behavior by which an animal escapes a predator or unfriendly partner. For instance C. elegans may be repelled by chemosensory signals to evade some pathogenic bacteria (Schulenburg and Ewbank, 2004; Schulenburg and Muller, 2004).


A normal process by which the maturing vulva (before eversion) turns inside out and the lumen closes during late L4 stage (post eversion). However, this same process can be overdone in some developmental mutants to create a distinctive mutant phenotype, Evl, in which the vulval tissue projects visibly outward from the ventral side of the body.

See Everted vulva

Everted vulva Evl

A mutant phenotype in which the developing vulva everts out of the body to form an large outward bulge which generally leaves the animal unable to undergo normal egg- laying.

See Multivulva phenotype

Excitatory synapse Inhibitory synapse (A)

A synaptic connection between two neurons whose stimulation leads to an increase in electrical activity in the postsynaptic cell (a depolarization).

Excretory canal  

The H-shaped structure made by the processes of the excretory canal cell. It extends almost the full length of the body on both sides of the animal, generally in contact with the lateral hypodermis and the pseudocoelom.

See Excretory system

Excretory cell

exc cell

Excretory canal cell (S)


A protokidney cell with an H-shaped internal lumen that is suggested to collect and secrete salt solutions outward via the excretory sinus (Nelson et al., 1983; Buechner et al., 1999). The animal cannot survive if this cell is ablated or if its outlet (the excretory duct) is blocked.

See Excretory system

Excretory duct Secretory-excretory duct (S)

The extracellular sinus formed by the excretory duct cell and the pore cell.

See Excretory system

Excretory duct cell

exc duct

Duct cell (S)


An interfacial epithelial cell which forms a lumen to receive the outflow of the excretory gland and excretory canal cells; this outflow is transported into the lumen of the excretory pore cell and then to the excretory pore.

See Excretory system

Excretory gland cell

exc gl L
exc gl R

Secretory-excretory gland (S)


A pair of large cells in the head that fuse to form a single gland whose contents are released into the excretory duct through a specialized secretory membrane. Under most conditions the gland is filled with large secretory granules containing a dense matrix of unknown function; however, in the dauer larva these granules are absent and the gland is filled with complex spherical and tubular membranes (Nelson et al., 1983). It has been postulated that the granules may contribute to the glycocalyx covering the body cuticle (Nelson and Riddle, 1984).

See Excretory system

Excretory junction Secretory membrane

A highly specialized intercellular membrane junction that links the excretory canal cell, the excretory gland process, and the excretory duct cell, to permit the release of materials from the canal and gland into the duct and hence out of the body.

See Excretory system

Excretory pore Pore (S)

The outlet of the excretory sinus to the exterior environment through the cuticle. Pore is located on the ventral side of the head, just behind the nerve ring.

See Excretory system

Excretory pore cell

exc pore

exc socket cell (S)

An interfacial epithelial cell which links excretory duct to hypodermis.

See Excretory system

Excretory socket cell

exc socket

exc pore cell (S)

G2p Older name for excretory pore cell.
Exocuticle   See Internal cortical layer
Expulsion motor contraction Exp or EMC

A specific step in the defecation motor program.

See Defecation motor program


A form of molting in which a nematode sheds a retained outer cuticle layer. This process is common in infective nematode species, but not in C. elegans. Infective species may retain an older cuticle layer as a protective sheath until they successfully enter their final host.

See Molt

Extensor muscle   Refers to any of several different specialized muscles in the male tail which extend either the gubernaculum or the spicules.
Extracellular matrix


Basal lamina (S)
Basement membrane (S)

A complex mixture of long chain proteins and proteoglycans that lie on the outer surface of cell membranes of each tissue, in particular those at the basal pole. Much of the material is condensed into a uniform meshwork, the basal lamina, but some collagenous materials may extend further into the pseudocoelom between neighboring tissues. For more general information see Alberts et al., 2002.

See Basal lamina
See Tendon



A pigmented granular structure found in pharyngeal muscles in some nematode species other than C. elegans (Burr and Webster, 1971; Bollerup and Burr, 1979). Such eyespots vary in color, are different from the background coloration of the rest of the pharynx, and usually organize into simple cup-shaped structures. Pigmented eyespots occur in other nematode species in association with sheath cells and a possible lens-like element in the bodywall of the head (Croll et al., 1972; Van de Velde and Coomans, 1988). Although lacking a detectable eyespot, C. elegans is reported to exhibit a behavioral response to light (Burr, 1985; Ken Miller, pers. comm.).

This section should be cited as: Herndon, L.A., Lints, R. and Hall, D.H. 2009. Glossary E. In WormAtlas.  doi:10.3908/wormatlas.6.5
Edited for the web by Laura A. Herndon. Last revision: December 12, 2013.