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accessory point Additional small point adjacent to tip of principal arm (primary branch) of a double claw.

adhesive disc Ventrally adhesive distal section of toe in certain tardigrades.

anhydrobiosis Cessation of metabolism initiated by desiccation of tardigrade. A form of cryptobiosis.

anoxybiosis In response to a lack of oxygen, tardigrades suspend metabolism. A form of cryptobiosis.

apophysis In digestive tract, cuticular thickening at the junction of buccal tube and pharyrngeal bulb; functions as a valve.

brain Main concentration of nerve tissue, composed of three median lobes and two lateral lobes lying over pharyngeal bulb and salivary gland.

buccal tube Section of digestive tract between mouth and pharyngeal bulb.

cephalic papilla In certain tardigrades, one of two sensory structures located near the mouth; typically short and broad.

cirrus (plural is cirri) Cuticular extensions from the anterior part of the body. Found in armored heterotardigrades.

cirrus A In plate bearing tardigrades, long, extension directed off anterior part of animal.

clavus Short blunt cuticular projection adjacent and posterior to base of cirrus A.

claw Variously shaped,hook-like structure at distal end of leg; size, shape, and arrangement are of taxonomic importance.

cloaca Term applied to posteriormost section of digestive tract in those tardigrades in which either oviduct or vasa deferentia open into rectum.

coelomocyte Storage cell which is found in fluid-filled body cavity.

cryobiosis Form of cryptobiosis that is triggered by a decrease in temperature. It is an ordered freezing of cells that preserves life.

cryptobiosis The suspension of metabolism due to an change in environment.

cuticle Noncellular, multilayered, variously ornamented layer covering outer surface of body and extending into both foregut and rectum.

dead man's float Appearance of tardigrade when in the anoxybiotic state. It is swollen, motionless, and all four legs are extended. It is a temporary state.

double claw Type of claw which is split into a larger principal arm and a smaller secondary arm. One or both of the arms (or branches) can have one or more points.

esophagus Tubular section of digestive tract between pharyngeal bulb and intestine.

external buccal cirri Pair of sensory externsions, one on each side of mouth in certain tardigrades.

eyespot Pair of dorsal pigmented, light sensitive cells on anterior end of body.

frontal plate In plate bearing tardigrade; anteriormost plate covering greater part of head and bearing eyespots.

furca Enlarged posterior end of stylet; typically split at end.

gonopore Opening of male or female reproductive system; opens either at anus or as a separate pore between third and fourth pair of legs.

internal buccal cirri Pair of sensory cirri, one on each side of mouth in armored tardigrades.

lunule Cutlicular thickening at base of claws in certain tardigrades, normally half-moon in shape.

macroplacoid Large cuticular thickenings in pharyngeal bulb; shape, number and arrangement are of taxonomic importance.

Malpighian tubule One of three glands, one located dorsally and two laterally, each consisiting of three cells. Opens into digestive tract at junction of intestine and rectum and functions to maintain internal salt and water balance.

median cirrus Terminal median cutlicular extension at anterior end of head in certain tardigrades; may be flanked by internal and external buccal cirri as well as cephalic papillae.

median plates 1-3 In plate-bearing tardigrade, small dorsomedian plates between scapular and first paired plates, between first and second paired plates, and between second and psuedosegmental or terminal plates, respectively.

microplacoid In digestive tract, small cuticular thickening posterior to macroplacoids within pharyngeal bulb; presence or absence is of taxonomic importance. (See also macroplacoid)

midgut intestine

mouth Anterior opening of digestive tract through which stylets are protruded during feeding; occasionally surrounded by peribuccal lamellae.

ovary Section of female reproductive system located above intestine and connected to gonopore via single oviduct.

oviduct Section of female reproductive system leading from dorsal ovary around right or left side of intestine to gonopore.

paired plates 1, 2 In plate-bearing tardigrade, large, often spine-bearing, dorsally divided plates extending down sides of body approximately at level of second and third leg pairs.

papillus Small sensory projection on one or more leg pairs in certain tardigrades. (See also cephalic papilla)

pedal ganglion Small ganglion in each leg; joined to central ganglion by nerve.

peribuccal lamellae Ring of small cuticular thickenings surrounding the mouth of certain tardigrades.

peribuccal papilla Raised knob-like structures surround the mouth.

pharyngeal bulb (pharynx) Muscular, bulbous section of digestive tract between the buccal tube and esophagus, typically with triradiate lumen and placoids.

pharyngeal tube portion (of buccal tube) Section of buccal tube between stylet supports and pharyngeal bulb.

pharynx pharyngeal bulb

placoid General term for variously elaborated, larger (macroplacoid) or smaller (microplacoid) cuticular elements within pharyngeal bulb.

principal arm In double-claw, larger of two arms. (See also secondary arm).

pseudosegmental plate Additional large plate, with or without median division, between the third median plate and the terminal plate in certain tardigrades

rectum (hindgut) Short, cuticle-lined section of digestive tract between the intestine and anus. (See also cloaca)

salivary gland Pair of large glands, one along each side of the buccal tube and pharyngeal bulb; opens anteriorly into buccal tube.

scapular plate In plate-bearing tardigrade, large plate posterior to frontal plate; extends down sides of body approximately at level of first leg pair.

secondary arm In doubleclaw, smaller of two arms. (See also principal arm)

seminal receptacle Small sac functioning for storage of sperm in females of certain tardigrades; opens opposite oviduct into cloaca.

seminal vesicle In male reproductive system, expanded section of sperm duct (vas deferens).

sperm duct vas deferens

spine Variously elongated (spine, filament) cuticular projection on leg and/or laterally, dorsolaterally, and dorsally on posterior margin of plates.

spur In certain tardigrades, small, curved hook, typically at base of internal claw, occasionally also of external claw.

stylet Pair of lance-shaped cuticular structures, one on each side of the buccal tube. Pointed anterior ends project into buccal tube; blunt posterior ends (furcae) joined to buccal tube by stylet supports.

stylet sheath Pair of sheath-like structures, one on each side of anterior end of buccal tube; encloses anterior end of stylet.

stylet support Pair of thin, elastic rods joining blunt ends (furcae) of stylets to buccal tube.

subpharyngeal ganglion First of five ventral ganglia; located below pharyngeal bulb and connected to brain by two connectives which surround pharyngeal apparatus.

terminal facet Ridge or keel formed by strong downward angulation of terminal plate.

terminal indentation One of two indentations on posterior margin of terminal plate; imparts plate with cloverleaf-like appearance.

terminal plate In plate-bearing tardigrade, posteriormost plate; extends down sides of body approximately at level of last leg pair.

testis Section of male reproductive system located above intestine and connected to gonospore via two vasa deferentia.

throttling Median constriction in macroplacoids in pharyngeal bulb.

toe Term applied to finger-shaped distal projection of legs bearing terminal adhesive discs; number and arragnement are of taxonomic importance

vas deferens (Sperm duct) Section of male reproductive system between testis and gonopore; may be expanded to form seminal vesicle.

ventral ganglion One of five ventral concentrations of nerve tissue (first = subpharyngeal ganglion) along longitudinal ventral nerve cords.

ventral nerve cord Pair of closely adjoining nerve cords extending from subpharyngeal ganglion to posterior end of body; bears series of ventral ganglia, one approximately at level of each leg pair.


Website Authors: Karen Lindahl and Professor Susie Balser in affiliation
with Illinois Wesleyan University. Last revised 1 Oct. 1999.