Insect Morphological Terminology

(Definitions after de la Torre-Bueno, 1989; Gullan and Cranston, 1994)

abdomen - the third (posterior) major division of an insect body.

acetabulum (pl. acetabula ) - the cavity into which an appendage is articulated.

acrotergite - the anterior part of a secondary segment, sometimes large (then called postnotum), often reduced.

air sac - thin-walled, dilated sections of the tracheae.

ametabolous - lacking metamorphosis. i.e. with no change in body form during development to adult, with immature stages lacking only genitalia.

amphipneustic - a respiratory system with anterior (thoracic) and posterior (abdominal) spiracles on each side of the body (see also apneustic , metapneustic , peripneustic , polypneustic ).

anal - in the direction or position of the anus, near the anus or on the last abdominal segment.

anamorphic (development) - development in which the immature stages have fewer abdominal segments than the adult (see epimorphic development ).

anastomosis (pl. anastomoses ) - the running together or intimate connection of any two lines such as wing veins, blood vessels or nerves; usually applied to wing veins or markings.

antenna (pl. antennae ) - paired, segmented, sensory appendages, lying usually antero-dorsally, on the head derived from the second head segment.

anterior - at or towards the front.

anthropogenic - caused by humans.

anus - the posterior opening of the digestive tract.

apical - at or towards the apex.

apodeme - an ingrowth of the exoskeleton, tendon-like, to which muscles are attached.

apneustic - a respiratory system without functional spiracles (see also amphipneustic , metapneustic , peripneustic , polypneustic ).

apod (larva) -a larva lacking true legs.

apterous - wingless.

basal - at or towards either the base or the main body, or closer to point of attachment.

benthos - the bottom sediments of aquatic habitats and/or the organisms that live there.

bifid spicule - cleft or forked, small needle-like spine present in some larval Trichoptera.

bivoltine - having two generations in one year (see multivoltine , univoltine ).

book lung - respiratory organs resembling slit-like openings situated ventrally on the abdomen (Clyne, 1969; Davies, 1986).

borer (adj. boring ) - the maker of burrows in dead or living tissue.

brachypterous - having shortened wings.

brood - a clutch of individuals that hatch at the same time from eggs produced by one set of parents.

carapace - the protective exoskeletal shield covering part or all of the dorsal and lateral thorax.

carina (pl. carinae ) - an elevated ridge or keel, not necessarily high or acute.

caudal - at or towards the anal (tail) end.

caudal filament - one of two or three terminal filaments.

caudal lamellae - one of two or three terminal gills.

cephalic - pertaining to the head.

cephalic fan - mobile, brush-like structure on the labrum of larval Culicidae, Dixidae and Simuliidae: Diptera.

cephalothorax - sometimes called prosoma (q.v.), anterior part of the spider body bearing the united head and thorax. (Clyne, 1969; Davies, 1986).

cercus (pl. cerci ) - one of a pair of appendages originating from abdominal segment eleven but usually visible as if on segment ten.

chelate - pincer-like.

chelicera (pl. chelicerae ) - the first pair of pincer-like appendages on cephalothorax, bearing the fangs (Clyne, 1969; Davies, 1986).

chitin - the major component of arthropod cuticle, a polysaccharide composed of subunits of acetyl-glucosamine and glucosamine.

claw (strictly, pretarsal claw , unguis ) - a hooked structure on the distal end of the pretarsus, usually paired, more generally, any hooked structure.

clypeus - the part of the insect head to which the labrum is attached anteriorly; lies below the frons, with which it may be fused in a frontoclypeus or separated by a suture.

compound eye - an aggregation of ommatidia, each acting as a single facet of the eye.

cosmopolitan - distributed worldwide (or nearly so).

coxa (pl. coxae ) - the proximal (basal) leg segment.

coxopodite - the basal segment of the leg, being homologous with the coxa.

cuticle - the external skeletal structure, secreted by the epidermis, composed of chitin and protein comprising several differentiated layers.

crepuscular - active at low light intensities, dusk or dawn (see also diurnal , nocturnal ).

crochets - curved hooks, spines or spinules on prolegs.

dens (pl. dentes ) - in Collembola, the long proximal segment bearing the mucro apically.

determinate (growth) - with a distinctive final, adult, instar (see indeterminate growth ).

detritivore (adj. detritivorous ) - an eater of organic detritus of plant or animal origin.

diapause - delayed development independent of environmental conditions.

dispersal - movement of an individual or population away from its birth site.

distal - at or near the furthest end from the attachment of an appendage (opposite to proximal).

diurnal - day active (see also crepuscular , nocturnal ).

dorsal - on the upper surface.

dorsum - the upper surface.

drift - passive movement due to water or air currents.

ectoparasite - a parasite that lives externally on, and at the expense of, another, which it does not kill (see also ectoparasitoid ).

ectoparasitoid - a parasite that lives externally on, and at the expense of, another, which it kills (see also ectoparasite ).

elytron (pl. elytra ) - the modified, hardened, fore wing of a beetle that protects the hind wing.

endemic - a taxon or taxonomic group that is restricted to a particular geographic area.

endite - an inwardly-directed (mesal) appendage or lobe of a limb segment.

endophallus - the inner, eversible tube of the penis.

endopterygote - development in which the wings form within pockets of the integument, with eversion taking place only at the larval--pupal moult (as in the monophyletic grouping Endopterygota).

epicoxa - a basal leg segment, forming the articular sclerites in all extant insects, believed to have borne the exites and endites that fused to form the evolutionary precursors of wings.

epicranial suture - a Y-shaped line of weakness on the vertex of the head where the split at moulting occurs.

epimeron (pl. epimera ) - the posterior division of the pleuron of a thorax, separated from the episternum by the pleural suture.

epimorphic development - development in which the segment number is fixed in the embryo before hatching (see epimorphic development ).

epipharynx - the ventral surface of the labrum, a membranous roof to the mouth.

epipodite - a lateral branch of a protopod (crustacean appendage).

eutrophication - nutrient enrichment, especially of water bodies.

exite - an outer appendage or lobe of a limb segment.

exopterygote development - development in which the wings form progressively in sheaths that lie externally on the dorsal or dorso-lateral surface.

exoskeleton - the external, hardened, cuticular skeleton to which muscles are attached internally.

external - on the outside.

fang - the hard, curved, piercing apical segment of the chelicerae, through which poison is conveyed (Clyne, 1969; Mascord, 1980).

femur (pl. femora ) - the third segment of an insect leg, following the coxa and trochanter; often the stoutest leg segment.

fore - anterior, towards the head.

frons - the single medio-anterior sclerite of the insect head, usually lying between the epicranium and the clypeus.

frontoclypeus - the combined frons and clypeus.

frontoclypeal (or epistomal ) suture - a groove that runs across the insect's face, often separating frons from clypeus.

furcula - the abdominal springing organ of Collembola.

gena (pl. genae ) - literally, a cheek; on each side of the head, the part lying beneath the compound eye.

genus (pl. genera , adj. generic ) - the name of the taxonomic category ranked between species and family; an assemblage of one or more species united by one or more derived features and therefore believed to be of a single evolutionary origin (i.e. monophyletic).

gill - a gas exchange organ, found in various forms in aquatic insects.

glossa (pl. glossae ) - the 'tongue', one of a pair of lobes on the inner apex of the prementum.

gonopore - the external opening of a genital duct; in the unmodified female the opening of the common oviduct, in the male the opening of the ejaculatory duct.

gula - a ventromedian sclerotized plate on the head of prognathous insects.

hair - a cuticular extension, also called a macrotrichium or seta.

head - the anterior of the three major divisions (tagmata) of an insect body.

hellgrammit e - the larva of Megaloptera.

hind - at or towards the posterior.

hydrostatic - of or pertaining to water pressure.

hydrostatic organs - crescent-shaped pigmented organs found on the lateral aspects of the thorax and near the caudal end of a few larval Chaoboridae: Diptera.

hypognathous - with the head directed vertically and mouthparts directed ventrally.

hypopharynx - a median lobe of the pre-oral cavity of the mouthpart.

hyporheic - living in the substrate beneath the bed of a waterbody.

imago (pl. imagines , imagos ) - the adult insect.

indeterminate (growth) - without a distinctive final, adult instar; with no definitive terminal moult (see determinate growth ).

insectivore (adj. insectivorous )- an insect eater.

instar - the growth stage between two successive moults.

keel - longitudinal ridge.

labial mask - in Odonata, mask (q.v.).

labial palp - a one to five-segmented appendage of the labium.

labium (adj. labial ) - the 'lower lip', forming the floor of the mouth, often with a pair of palps and two pairs of median lobes, derived from the sixth head segment.

labrum (adj. labral ) - the 'upper lip' forming the roof of the preoral cavity and mouth; derived from the first head segment.

lacinia - the mesal lobe of the maxillary stipes.

lacinia mobilis - a mobile tooth-like appendage of the mandibule.

larva (pl. larvae ) - an immature insect after emerging from the egg, often restricted to insects in which there is complete metamorphosis (holometaboly), but sometimes used for any immature insect that differs strongly from its adult (see also nymph ).

larval eye - the 'simple' eye of many larval insects, sometimes aggregated into a more complex visual organ (see stemmata ).

lateral - at, or close to, the side.

lentic - of standing water.

ligula - the glossae plus paraglossae of the prementum of the labium, whether fused or separate.

longitudinal - in the direction of the long axis of the body.

lotic - of flowing water.

maggot - a legless larval insect, usually with a reduced head, frequently a fly.

mandible (adj. mandibular ) - the jaws, either jaw-like in shape in biting and chewing (mandibulate) insects, or modified as narrow stylets in piercing and sucking insects; the first pair of jaws; derived from the fourth head segment.

mandibulate - possessing mandibles.

manubrium (pl. manubria ) - in Collembola, the base of the springing appendage (furcula) bearing the dens.

maxilla (pl. maxillae ) - the second pair of jaws, jaw-like in chewing insect, variously modified in others, derived from the fifth head segment.

maxillary palp - a one to seven-segmented sensory appendage borne on the stipes of the maxilla.

median - at or towards the middle.

mentum - the ventral fused plate derived from the labium.

mesal - nearer to the midline of the body, also medial.

mesothorax - the second (and middle) segment of the thorax.

metamorphosis - the relatively abrupt change in body form between the end of immature development and the onset of the imaginal (adult) phase.

metapneustic - a respiratory system with only the last abdominal spiracles on each side of the body (see also amphipneustic , apneustic , peripneustic , polypneustic ).

metathorax - the third (and last) segment of the thorax.

microtrichium (pl. microtrichia ) - a subcellular cuticular extension, usually several to very many per cell.

molar area - the grinding surface of the mandible.

moulting - the formation of new cuticle followed by ecdysis.

mouthhooks - the head skeleton of the maggot larva of higher flies.

mucro - (pl. mucrones ) - in Collembola, the terminal segment of the springing appendage, arising from the apex of the dens.

multivoltine - having several generations in one year (see bivoltine , univoltine ).

naiad - an alternative name for the immature stages of aquatic hemimetabolous insects (see nymph , larva ).

nauplius eye - the central eye in Crustaceans in (usually) the first larval stage after leaving the egg.

nocturnal - active at night (see also crepuscular , diurnal ).

notopleural suture - the suture separating the pronotum from the proepisternum.

nymph - an immature insect after emerging from the egg, usually restricted to insects in which there is incomplete metamorphosis (hemimetaboly) (see also larva ).

occipital foramen - the opening of the back of the head.

occiput - the dorsal part of the posterior cranium.

ocellus (pl. ocelli ) - the 'simple' eye of adult and nymphal insects, typically three in a triangle on the vertex, with one median and two lateral ocelli; the stemma of some holometabolous larvae.

oligopod (larva) - a larva with legs on the thorax and not on the abdomen

ommatidium (pl. ommatidia ) - a single element of the compound eye.

ontogeny - the development from egg to adult.

open tracheal system - a gas exchange system comprising tracheae and tracheoles and with spiracular contact with the atmosphere (see closed tracheal system).

opisthognathous - with the head deflexed such that the mouthparts are directed posteriorly, as in many Hemiptera (see also hypognathous , prognathous ).

ovoviviparity - retention of the developing fertilised egg within the mother, considered to be a form of viviparity (producing living offspring) but in which there is no nutrition of the hatched young (see oviparity, viviparity).

paedogenesis (adj. paedogenetic ) - reproduction in an immature stage.

pala (pl. palae ) - in Corixoidea: Hemiptera, tarsus of foreleg modified into a hair-fringed scoop for particle feeding.

palp or palpus (pl. palps or palpi ) - finger-like, usually segmented appendages of the maxilla and labium (labial palp).

paraglossa (pl. paraglossae ) - one of a pair of lobes distolateral on the prementum of the labium, lying outside the glossae, but mesal to the labial palp.

parthenogenesis - development from an unfertilised egg.

patella (pl. patellae ) - the short, fourth leg segment between the femur and tibia (Cloudsley-Thompson, 1968).

pedicel - the stem or stalk of an organ; the second antennal segment.

pedipalp - six-segmented, second pair of appendages of the cephalothorax, corresponding to the mandibles of insects.

peripneustic - a polypneustic respiratory system with nine functional spiracles on each side of the body: one mesothoracic and eight abdominal (see also amphipneustic , apneustic , metapneustic , polypneustic ).

pharate - within the cuticle of the previous stadium, 'cloaked'.

pharynx - the anterior part of the foregut, anterior to the oesophagus.

phylogeny - evolutionary history (of a taxon).

phytophage (adj. phytophagous ) - an eater of plants.

phytophagy - the eating of plants.

polypod (larva) - a type of larva with jointed legs on the thorax and prolegs on the abdomen.

polypneustic - a respiratory system with at least eight functional spiracles on each side of the body (see also amphipneustic , apneustic , metapneustic , peripneustic ).

posterior - at or towards the rear.

postnotum - the posterior part of a pterothoracic notum, bearing the phragmata that support longitudinal muscles.

predation - preying on other organisms.

predator - an organism that eats more than one other organism during its life.

prementum - the free distal end of the labium, usually bearing labial palps, glossae and paraglossae.

prey - a food item for a predator.

proboscis - a general term for elongate mouthparts, see also rostrum.

procercus - in larval Chironomidae: Diptera, preanal tubercle carrying one to twenty apical setae and usually two lateral setae.

prognathous - with the head horizontal and the mouthparts directed anteriorly (see hypognathous , opisthognathous ).

proleg - an unsegmented leg of a larva.

pronotum - the upper (dorsal) plate of the prothorax.

prosternal horn - a membraneous, finger-like projection of the prosternum present in many larval Trichoptera.

prothorax - the first segment of the thorax.

proximal - the part of an appendage closer to or at the body (opposite to distal).

pterothorax - the fused meso- and metathorax of some winged insects.

pupa (adj. pupal ) - the inactive stage between larva and adult in holometabolous insects; also termed a chrysalis in butterflies.

puparium - the hardened skin of the final-instar larva (higher Diptera) in which the pupa forms.

pupation - becoming a pupa.

ramus (pl. rami ) - a branch (as of a limb).

raptorial - adapted for capturing prey by grasping.

rectum (adj. rectal ) - the posterior part of the hindgut.

rostrum - a facial extension that bears the mouthparts at the end (see also proboscis ).

sclerite - a plate on the body wall surrounded by membrane or sutures.

sclerotization - stiffening of the cuticle by cross-linkage of protein chains.

scutellum - the posterior third of the alinotum (either meso- or metanotum), lying behind the scutum.

semi-aquatic - living in saturated soils, but not immersed in free water.

seta (pl. setae ) - a cuticular extension, a trichoid sensillum , also called a hair or macrotrichia.

spine - multicellular unjointed cuticular extension, often thorn-like.

spinneret - small, tubular abdominal appendages from which silk threads are exuded by spiders.

spinule - a small spine (see microtrichia ).

spiracle - an external opening of the tracheal system.

spur - an articulated spine.

stadium - the period between moults, the instar duration or intermoult period.

stemma (pl. stemmata ) - the 'simple' eye of many larval insects, sometimes aggregated into a more complex visual organ.

sternite - the diminutive of sternum, a subdivision of a sternum.

sternum (pl. sterna , adj. sternal ) - the ventral surface of a segment.

stylet - one of the elongate parts of piercing/sucking mouthparts, a needle-like structure.

subimaginal instar , see subimago .

subimago - in Ephemeroptera, the winged penultimate instar; subadult.

suture - an external groove that may show the fusion of two plates.

symbiosis - a long-lasting, close and dependent relationship between organisms of two different species.

tarsomere - a subdivision of the tarsus (q.v.).

tarsus (pl. tarsi ) - the leg segment distal to the tibia, comprising one to five tarsomeres and apically bearing the pretarsus.

taxon (pl. taxa ) - any taxonomic unit (species, genus, family, phylum, etc.).

taxonomy (adj. taxonomic ) - the theory and practice of naming and classifying organisms.

tentorium - the endoskeleton of the head, including anterior and posterior tentorial arms - cuticular invaginations.

tergum (pl. terga , adj. tergal , dim. tergite ) - the dorsal surface of a segment.

tergite - the diminutive of tergum, a subdivision of the tergum.

thorax - the middle of the three major divisions (tagma, q.v.) of the body, comprising pro-, meso- and metathorax.

tibia (pl. tibiae ) - the fourth leg segment, following the femur.

trachea (pl. tracheae ) - a tubular element of the insect gas exchange system, within which air moves.

tracheal system - the insect gas exchange system, comprising tracheae and tracheoles.

tracheole - the fine tubules of the insect gas exchange system.

transverse - at right angles to the longitudinal axis.

trochanter - the second leg segment, following the coxa.

trochantin - a small sclerite anterior to the coxa.

tubercle , tubercule - a small knob-like or rounded protuberance.

uncate - barbed or hooked.

univoltine - having one generation in one year (see bivoltine , multivoltine ).

vagina - a pouch-like or tubular genital chamber of the female genitalia.

venter - the lower surface of the body.

ventilate - to pass air or oxygenated water over a gas exchange surface.

ventral - towards or at the lower surface.

vertex - the top of the head, posterior to the frons.

viviparity - the bearing of live young.

voltinism - the number of generations per year.

xylophage - (adj. xylophagous ) - an eater of wood.