amixis: Reproduction that normally proceeds without fertilization, although mixis is still possible.

amphid: One of two chemosensory/secretory structures on the anterior end of nematodes, located midlaterally or slightly dorsosublaterally. The amphids of many soil nematodes are very small and inconspicuous, while they are often distinct in aquatic nematodes. 
(Fig.) 

amphidelphic: Female reproductive system with two branches diverging in opposite directions from the vagina.
(Fig.)  (anterior branch)  (posterior branch of the same nematode)

amphimixis: Reproduction through cross fertilization.

anus: The exit opening of the digestive tract. It is usually a curved slit, and sometimes a tiny pore. 
(Fig.) 

apomixis: Reproduction that never involves fertilization. 

automixis: Reproduction through self-fertilization.

basal bulb: The  swollen posteriormost  part of the pharynx, also referred to as end bulb or in some cases gland bulb. In Rhabditina and Cephalobina, the basal bulb is distinctly spherical to pyriform, and contains three finely striated transverse  valves sometimes referred to as butterfly valves.
(Fig.) (with transverse valves)  (without valves)  (overlapping gland bulb)

basal lamina: A very thin extracellular layer surrounding or supporting epithelial cells (usually only visible with electron microscopy).

Brenner, Sidney:  A visionary scientist who led a research group in the 1970s that established the use of Caenorhabditis elegans as a powerful model for addressing many biological questions. 

buccal capsule: The cuticle of the stoma, in other words the lining of the digestive tract between the mouth opening and the beginning of the pharyngeal corpus.
(Fig.) 

buccal cavity: The lumen of the stoma, in other words the cavity of the digestive tract bounded by the mouth opening, the beginning of the pharyngeal corpus, and the buccal capsule.
(Fig.) 

bursa: Also called caudal alae. A sucker- or cap-shaped cuticular structure on the male posterior end, consisting of two cuticular flaps, wings or alae which jointly constitute the velum. The bursa can be leptoderan  or peloderan, and often includes genital sensilla modified into rays. It is called "open" if the two wings do not join anterior to the cloacal opening, and "closed" if they do. 
(Fig.) 

caudal alae: see –bursa”

cheilostom: The anteriormost main region of the stoma, bounded by cuticle of the lips and (if present) labial probolae. 
(Fig.) 

cloaca: An internal cavity located at the junction of the digestive and male reproductive system. In most male nematodes, the cloaca contains spicules and a gubernaculum.

convergent evolution:  The expression of characters that are similar as a result, not of a shared evolution, but due to separate evolutionary events

corpus: The anterior part of the pharynx proper, i.e. the anteriormost region in which the lumen has a triradiate cross-section that is not triangular but more or less Y-shaped. 
(Fig.) 

cuticle: The extracellular layer(s) covering the cells of the body wall and lining parts of the digestive tract.
(Fig.) 

deirid: A sensory structure in the lateral field, usually located near the basal bulb. It is often papilliform in males and cryptic (i.e. invisible even with SEM) in females. 
(Fig.) 

determinate cleavage: Development in which the destiny of each cell is determined early in development and these early cells are  not readily adaptable to an alternate destiny. 

didelphic: Female reproductive system with two (apparently) functional ovaries.
(Fig.) anterior andposterior ovary in P. minor

endotokia matricida: Internal hatching of eggs and development of juveniles, resulting in the death of the parent animal.

entomopathogenic: Life style characterized by the transmission of  bacteria fatal to an insect host, followed by nematode repoduction inside this dead insect.

entomophilic:  Life style characterized by parasitizing insects.

esophagus: see –pharynx”

excretory  pore: The opening of the excretory-secretory  system, usually located near the nerve ring and deirids. 
(Fig.) 

freeliving:  Life style characterized by lack of parasitism.

genital papillae: Sensory structures occurring only on the tail of adult male nematodes (see also papilla).
(Fig.) 

gonochorism: Reproduction through the fusion of two types of gametes, produced by separate sexes.

gubernaculum: A more or less complex sclerotization of the dorsal wall of the cloaca in male nematodes. It serves to anchor and guide the spicules during copulation.
(Fig.) 

gymnostom: The middle region of the stoma, bounded by so-called arcade epidermis. 
(Fig.) 

haplodiploidy: Sex determination mechanism by which females are diploid and males are haploid.

hermaphrodi(ti)sm: Reproduction through the fusion of two types of gametes produced by the same individual(s).

hydrostatic skeleton:  A system of maintaining body integrity (in place of a true skeleton) by the effect of fluid pressure against  resistance provided by the body wall. 

hypodermis: A living layer of the body wall that underlies and secretes the cuticle, and also includes –hypodermal chords” that run the length of the body, protruding into the body cavity in between the four sectors of somatic musculature. The lateral hypodermal chords contain the nuclei of the hypodermal cells, and sometimes also parts of the excretory system, while the dorsal and ventral chords contain nerves.
(Fig.) 

isthmus: The middle part of the pharynx, between corpus and basal bulb. The isthmus is always more slender than the corpus. (Fig.) 

lateral field: Also known as lateral alae. An area of the body cuticle with one or more longitudinal ridges overlying the lateral hypodermal chords. 

lumen: The cavity inside a tubular organ or other open-ended hollow structure.

median bulb: A strongly muscular swollen structure that may occur in the posterior region of the pharyngeal corpus. Sometimes the median bulb contains sclerotized longitudinal valves.
(Fig.) 

metacorpus: The median bulb, or by extension the region homologous to the median bulb in nematodes without posteriorly swollen pharyngeal corpus.
(Fig.) 

monodelphic: Female reproductive system with only one functional ovary.
(Fig.) anterior and only ovary in P. penetransposterior and only ovary in X. hygrophilum

nerve ring: A ring of nerve fibers surrounding the digestive tract (usually the pharynx) of nematodes. It is often quite difficult to see in preserved specimens. 
(Fig.) (overview in different pharynx types)(an unusually clear example)

ocellus: Also known as eyespot. Ocelli are sensilla capable of detecting light. They are relatively rare in nematodes.
(Fig.)

oesophagus: see –pharynx”

odontophore: In nematodes with an odontostyle, the cuticle lining the pharynx is usually weakly or strongly thickened just posterior to the odontostyle. This thickened cuticle is the odontophore.
(Fig.) 

odontostyle: A spear assumed to be derived from modification of a single tooth that has become a straight, hollow tube with tapering tip. A true odontostyle occurs only in the order Dorylaimida, and usually consists of a single part. However, it can sometimes be confused with a stomatostylet if the odontophore is strongly sclerotized.
(Fig.) 

onchiostyle: A spear-like slender tooth that is curved and not truly hollow. An onchiostyle only occurs in the family Trichodoridae.
(Fig.) 

opisthodelphic: Female reproductive system directed posteriad from the vagina.
opisthodelphic system in X. hygrophilum

ovary: The female germinative organ, producing oocytes. In many nematodes, it can be recognized under light microscope through the gradually increasing size and opacity of its oocytes from  germination zone to ripening zone. 
(Fig.) 

oviduct: A usually short cellular canal connecting ovary to uterus. In amphimictic species, it is the site of fertilization of oocytes by sperm cells. In Cephaloboidea and some Panagrolaimoidea, the junction of oviduct and uterus bears an anteriorly directed offset spermatheca. In other nematodes, the oviduct can be distended into an axial spermatheca. The oviduct is easily obscured by eggs or oocytes.
(Fig.) 

papilla: A protruding sensillum that is not hair-like or tube-like, but shorter than wide and rounded. Papillae are assumed to be mechanoreceptors only.
(Fig.) 

parthenogenesis: Reproduction without fusion of gametes or gamete nuclei.

peloderan: A bursa that extends over the tail tip.
(Fig.) 

pharynx: Also known as (o)esophagus. The anterior major organ in the digestive system. It often has a triradiate lumen, is bounded by its own basal lamina, and is of mixed ectodermal and mesodermal origin. The pharynx is often wholly or partly muscular because it usually acts as a pump that sucks food into the mouth and transports it into the intestine.
(Fig.) 

phasmid: A sensory/secretory opening on each side of the body, usually (but not always) located midlaterally on the tail. In male nematodes, SEM is often required to distinguish the phsmid from genital papillae. 
(Fig.) 

phytoparasite: Life style characterized by parasitizing plants

plant parasite: see –phytoparasite”

postvulval sac: A blind sac extending posteriorly from the vagina in many (but not all) prodelphic-monodelphic female nematodes. Also called the postvulval uterine branch (PUB) or postvulval uterine sac (PUS). It is assumed to be a rudimentary posterior uterus, although its cell structure and texture usually differs from that of the anterior uterus.
(Fig.) 

predator: Life style characterized by feeding on small animals such as other nematodes.

probola: One of two types of cuticular processes projecting anteriorly from the lip region in a tri- or hexaradiate pattern of symmetry. Probolae are purely cuticular and contain neither nerve nor muscle cells. They appear to serve as scoops, brushes or flow guides with which bacteria are collected and diverted towards the mouth while the nematode moves through the soil.
(Fig.) 

procorpus: In species with a median bulb, the slender region of the phrayngeal corpus that lies anterior to the median bulb. In species without a median bulb, this term can be used to denote the anterior part of the corpus homologous to the former case. (Fig.) 

prodelphic: Female reproductive system directed anteriad from the vagina.
(Fig.) prodelphic system in P. penetrans

pseudocoelom:  A body cavity that, unlike a true coelom, does not develop in the gastrula from a secondary invagination of the mesoderm. Rather it  develops between the endoderm and ectoderm. In the adult it is considered to persist as a fluid-filled sac. 

pseudocoelomate: Describing  a group of phyla that are considered to have a pseudocoelom.  Recent evidence suggests that this grouping is artificial and is not the product of shared evolution. 

pseudogamy: Reproductive mechanism whereby sperm penetration stimulates completion of oocyte meiosis, but no fusion of occurs sperm and oocyte pronuclei.

radius: One of the three arms of the pharyngeal lumen on transverse section.

ray: A genital sensillum resembling a tube, usually incorporated in the wings of the bursa. It is often impossible to distinguish the phasmids from genital sensilla if a bursa is present, and the phasmids are then also counted as rays.
(Fig.)

rectum: The cuticular exit of the digestive system leading to the anus.
(Fig.) 

sensillum: A sensory structure capable of receiving stimuli from the external environment. Nematodes have many different types of sensilla, depending on whether they e.g. protrude above the cuticle or not, or whether they have an external opening or not.
(Fig.)

seta: A protruding sensillum that is longer than wide and often pointed, more or less resembling a microscopic hair. Most setae are assumed to be mechanoreceptors only, although some may have an adhesive function.
(Fig.)

spear: A hollow needle-like structure in the stoma of some groups of nematodes, used for piercing food items and ingesting their contents.
(Fig.) 

spermatheca: A flexible sac or expansion of the female reproductive system. In amphimictic and hermaphroditic species, it serves as storage site for sperm. In parthenogenetic species, it presumably seves no purpose and is usually less clearly developed. The spermatheca may be difficult to see, especially when large oocytes or eggs are present.
(Fig.) 

spicule: One of (usually) two male copulatory organs in nematodes.
(Fig.) 

stegostom: The posteriormost part of the stoma, encircled by the anteriormost muscle and epidermis cells of the pharynx. 
(Fig.) 

stoma: The entry region of the digestive system, between mouth opening and pharyngeal corpus. It consists of the buccal capsule and the buccal cavity, and can often be subdivided further by the presence of various sclerotizations, or on the basis of surrounding cell types. 
(Fig.) 

(stomato)stylet: A spear assumed to be derived from fusions of different parts of the stoma, and especially different parts of the buccal capsule. A stomatostylet occurs in the order Tylenchida and usually consists of three parts: an anterior cone, a central shaft and posterior knobs.
(Fig.) 

total cleavage:  Early development in  which the –egg” lacks a yolk so that it divides in its entirety to form an embryo.

triploblastic:  Development which results in three germ layers: ectoderm, endoderm and mesoderm.

uterus: That part of the female reproductive system where the egg shell is formed. In amphimictic species, it usually extends from the point of fertilization of oocytes to the vagina. 
(Fig.) 

vagina: The cuticular channel connecting the female reproductive tract(s) to the vulva. 
(Fig.) 

vulva: The female genital opening, usually shaped as a transverse slit, a pore or a longitudinal slit.
(Fig.)