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Glossary of Morphological Terms


(Morphological figures, indices and measurements)

Abdomen. The third, posterior major division of the body. In ants, this also includes the propodeum, which is fused to the thorax and appears to be a thoracic segment, as well as the petiole and postpetiole (if present) found between the propodeum and the gaster.
Aciculate. Finely striate, as if scratched by a needle.
Acidopore. The orifice of the formic acid projecting system found in the subfamily Formicinae. It is formed from the apex of the Hypopygium and usually appears as a short nozzle, generally fringed with short setae at its apex.
. Tapering to a fine point.
Acute. Sharply angulate (less than 90 degrees)
Aedeagus. The penis.
Alate. Winged, both males and queens may have wings.
Alitrunk. The second, middle major division of the body. It consists of the thorax (the true thorax) and the first segment of the true abdomen (the propodeum), which is fused to the rear of the thorax. The alitrunk is sometimes called the mesosoma.
Alveolate. Honeycombed and with alveoli (cup shaped depressions) each of which contain a hair.
Anal cell. The space between the anal veins.
Antenna (plural: antennae). One of the paired, flexible, segmented sensory appendages on the head. The antenna consists of an elongate basal segment, the scape, followed distally by 3-11 smaller segments, which taken together form the funiculus.
Antennal condyles. The narrowed, neck-like portions of the first antennal segment that connect to the head surface.
Antennal fossa. The cavity or depression of the head where the antenna is articulated from.
Antennal scrobe. A groove, impression, or excavation found on the side of the head running above or below the eye that accommodates the antennal scape and sometimes the entire antenna.
Antennomere. Antennal segment.
Anterior tentorial pits. A pair of pits or impressions found anteriorly on the dorsal surface of the head, at or near the posterior clypeal margin. The pits indicate the points of attachment of the anterior arms of the internal skeleton (tentorium) of the head to the head capsule.
Apical. At or near the tip.
Appressed. Referring to a hair running parallel or almost parallel to the body surface.
Arcuate. Curved, bow-like.
Areolate. Being divided into a number of small and irregular spaces or cavities.
Arolium (plural: arolia). Pad-like structure found between the tarsal claws.
Basal lamella. A thin strip of cuticle found on the apical margin proximal to any teeth that may be present.
Basitarsus. First segment of the tarsus.
Bidentate. Bearing two teeth.
Buccal cavity. Mouth cavity.
Carina. Elevated ridge or keel.
Carinate. Having carinae, especially in parallel rows.
Carinula. A small carina.
Cephalic. Pertaining to the head.
Clavate, claviform. Thickened, especially near or at the tip.
Clypeus (plural: clypei). The foremost section fob the head, just behind the mandibles and demarcated posteriorly by a transverse suture.
Condyle. A structure that articulates any appendage to the body surface.
Cordate. Heart-shaped.
Corrugated. Wrinkled with alternative and parallel ridges and channels.
Costa. A ridge or keel that is rounded at the top.
Costate. Having costae, especially in parallel rows.
Costula. A small costa.
Costulate. Having costulae, especially in parallel rows.
Coxa (plural: coxae). The basal, or first segment of the leg, that attaches the leg to the body.
Dealate. Having shed the wings.
Declivity. Downward sloping surface, such as the posterior face of the propodeum.
Decumbent. Referring to a hair standing 10 to 40 degrees from the body surface.
Dentate. Toothed, as in the dentate inner borders of mandible.
Denticulate. With minute teeth or tooth-like structures.
Depressed. Flattened down.
Diastema. A relatively large and obvious gap between two adjacent teeth on the mandible.
Distal. Farthest away from body.
Dorsal. Upper surface, the dorsum.
Dorsoventral. Along a line drawn from the upper to lower surface.
Dorsum. Upper surface.
Emarginate. Notched, with a shape seemingly cut from the margin.
Entire. Referring to a smoothly unbroken margin.
Epinotum. An older, alternative name for the propodeum, the first segment of the abdomen, which is fused to the rear part of the thorax.
Erect. Referring to a hair standing nearly to straight up from the body surface.
Excised. With a deep cut or notch.
Eye. Referring to the compound eye, composed of few to many separate ommatidia, or facets.
Facet. The ommatidium, a basic unit of the compound eye.
Falcate. Sickle-shaped.
Femur (plural: femora). The third segment of the leg away from the body, following the coxa and trochanter.
Fenestra. A translucent cutilar thin spot.
Filiform. Thread-like, as often seen in the antennal funiculus with the segments all of about the same size.
Flagellate. Whip-like.
Foramen. An opening or impressed pit.
Fossa (plural: fossae). A relatively large and deep pit, such as the antennal fossa on the head where the first antennal segment is inserted.
Fovea (plural: foveae). A deep depression with well marked sides.
Foveate. Having multiple foveae (deep pits with well marked sides).
Foveolate. Having multiple small, deep pits that are deeper and larger than punctures, giving a coarser appearance.
Frons. Area above the clypeus, approximately in the center of the front of head. The frontal triangle, which is roughly triangular in shape and demarcated by grooves, is often included in this area.
Frontal area. The frons.
Frontal carina. A pair of longitudinal ridges on the head found dorsally behind the clypeus and between the antennal sockets. They vary in length and may be short and simple, longer and extending back to occipital margin, are vestigial or absent.
Frontal clypeal suture. Suture fro ming the posterior margin of the clypeus.
Frontal triangle. The triangular shaped area usually found in the frontal area of head.
Funiculus (plural: funiculi). All of the antennal segment taken together, except for the basal segment, the scape.
Gaster. The somewhat globular terminal four of five segments of the abdomen, immediately posterior to the waist.
Gena (plural: genae). The area of the front of head bounded in front by the posterior margin of clypeus, behind by the anterior margin of eye, and medially by the antennal socket. Sometimes called the cheek.
Girdling constriction. A constriction or sudden and obvious narrowing of an abdominal segment that runs around the entire circumference of the segment.
Glabrous. Smooth, without hair, and shining.
Gula. An older term referring to the central part of the lower surface of the head, this area should be referred to as the hypostoma.
Hair. A seta.
Head. The foremost part of the body containing the antennae, eyes, and mandibles.
Helcium. The much reduced and specialized presclerites of abdominal segment 3 that form a complex articulation within the posterior foramen of the petiole.
Humerus (plural: humeri). The "shoulder", anterior corners of the pronotum (the first segment of the thorax.
Hypopygium. The last sternite (a lower plate) of the abdomen.
Hypostoma. The anteroventral region of the head; that area of cuticle just behind the buccal cavity and forming its posterior margin. Sometimes called gula.
Hypostomal teeth. One or more pairs of triangular to rounded teeth that project forward from the anterior margin of the hypostoma.
Inferior. In a lower anatomical position.
Joint. A segment, such as a joint of the antenna.
Labial palps. A pair of jointed appendages (sensory palps) that arise anterolaterally from the labium and having a maximum of 4 segments.
Labium. The second maxilla, which forms a lower lip beneath the maxillae.
Labrum. A broad lobe suspended from the clypeus above the mouth and forming and upper lip.
Lamella. A thin plate-like process.
Lanuginous. Down-like or wooly.
Leg segments. An appendage, used for locomotion or support and consisting of a basal coxa that articulates from the alitrunk, followed in order by a small trochanter, a long femur (often somewhat stout), a tibia, and a tarsus, which consists of five small segments and terminating in a pair of claws apically.
Lobiform. Lobe-shaped.
Macrochaetae. Large, standing, setae, often barbulate (barbs are often small and high magnification is needed to veiw them); sometimes referred to as pilosity. Common in such genera as Paratrechina.
. The first pair of jaws, usually with teeth. These appendages are used by ants to manipulate their environment and vary in size, shape, and dentition.
Maxilla (plural: maxillae). The second pair of jaws, usually folded beneath the first pair of jaws, the mandibles.
Maxillary palps. The pair of jointed sensory appendages (palps) that arise from the maxillae with a maximum of 6 segments.
Median. The middle.
Mesopleuron (Plural-Mesopleura). The middle and largest pleuron of the thorax, sometimes divided by a transverse groove in an upper area, the anepisternum, and a lower area, the katepisternum.
Mesonotum. The tergite of the mesothorax (the second or middle part of the thorax).
Mesosoma. The middle of the three major body parts, also called the alitrunk.
Mesothorax. See thorax.
Metanotal groove. A transverse groove or impression separating the mesonotum and propodeum.
Metanotum. The tergite of the metathorax (the third or last segment of the thorax).
Metasternal process. A paired cuticular projection of the posteroventral alitrunk sometimes present. When present, found astride the ventral midline, anterior to the apex of the cavity that the petiole articulates and near the level of the anterior margins of the metacoxal cavities.
Metathorax. See thorax.
Metatibia. Tibial segment of the metathorax (third or hind part of thorax).
Metatibial gland. A gland thought to be and exocrine gland, found ventrally on the metatibia posterior to the tibial spur.
Node. A rounded, knob-like structure as in the petiolar node, the upper rounded part of the petiole.
Nuchal collar. A ridge on the head found posteriorly and separating the dorsal and lateral surfaces from the occipital surface.
Occipital lobes. The rear corners of the head.
Occipital margin. The transverse posterior margin of the head in full-face view; actually this term is incorrect morphologically, as the occiput proper usually begins behind this level, but the name is acceptable for most purposes.
Occiput. Referring to the rearmost part of the head.
Ocular-malar space. Space between the anteriormost edge of eye and anteriormost section of head at the point where mandible is inserted (measured in profile view).
Ocellus (plural: ocelli). One of the simple, bead shaped eyes found in the rear central part of the head.
Ommatidium (plural: ommatidia). A facet, or unit, of the compound eye.
Paramere. Two lateral processes sheathing the male aedeagus.
Pectinate. Comb-like, such as some structures including the tibial spurs.
Pedicel. Either the "waist" (petiole and postpetiole combined) or the the second segment of the antenna from the base outward. When referring to the segment(s) found between the alitrunk and gaster, waist is the preferred term.
Pedunculate. Stalk-like, or set on a stalk or peduncle.
Petiole. The first, and sometimes the only, segment of the waist, found between the propodeum and the gaster.
Phragmotic. Sharply truncated as seen in the overall front of the head of some stem dwelling Camponotus, subgenus Coloboposis species.
Piligerous. Bearing a hair.
Pilosity. The longer and stouter hairs that stand above the shorter and usually finer hairs that make up the pubescence. Sometimes referred to as macrochaetae, especially if barbulate.
Pleurite/pleuron. The lateral sclerites of the thorax proper, excluding the propodeum (which is actually the first segment of the abdomen, but fused to the thorax).
Plumose. Referring to hairs that are multiply branched and feather-like in appearance.
Postpetiole. The second segment of the waist, some ants do not have a postpetiole.
Presclerite. A distinctly differentiated anterior section of an abdominal sclerite and separated from the remainder of the sclerite by a ridge, constriction, or both.
Pretarsal claws. A pair of claws on the pretarsal (apical) tarsal segment of the leg.
. Terminal segment of the foot, with a pair of claws and usually an arolium, or central pad.
Pronotum. The tergite of the prothorax (the first segment of the thorax).
Propodeal spine. Spine present on ants and articulating from the propodeum.
Propodeum. The first abdominal segment that is fused to the rear of the thorax, also called the epinotum.
Promesonotal suture. The transverse suture on the dorsum of the alitrunk separating the pronotum from the mesonotum.
Promesonotum. The fused pronotum and mesonotum taken together.
Prothorax. See thorax.
Proximal. Closest with reference to the body.
Pruinose. With a frosted or slightly dusted appearance.
Psammophore. Basket-like grouping of long, curved hairs found beneath the head of some ants.
Pubescence. Very short, fine hairs, usually forming a second layer beneath the pilosity.
Punctate. Having fine punctures like pinpricks.
Punctures. Small, pinpoint impressions in the exoskeleton.
Pygidium. The last complete tergite (upper plate) of the abdomen.
Replete. Swollen with liquid food.
Reticulate. Being covered with a network of carinae, striae, or rugae.
Reticulate-punctate. Being covered with a network of carinae, striae, or rugae with punctures in the interspaces.
Ruga (plural: rugae). A wrinkle.
Rugoreticulate. A network or grid formed by rugae.
Rugose. Having multiple wrinkles, usually running parallel.
Rugula (plural: rugulae). Small wrinkle.
Rugulose. Having multiple small wrinkles, usually running parallel.
Scabrous. Roughly and irregularly rugose.
Scape. The first, elongate segment of the antenna next to the head.
Sclerite. A general term for any single plate of the exoskeleton.
Scrobe. Large groove for the reception of an appendage, such as the antennal scrobe.
Segment. A joint.
Serrate. With teeth along the edge, saw-like.
Seta (plural: setae). Hair.
Shagreened. With a fine and close set roughness, such as shark skin.
Spiracle. An orifice of the tracheal system where gases enter and leave the body. Ants have 9 or 10 spiracles on each side of the body.
Spongiform tissue or process. Specialized sponge-like external cuticular tissue found mainly on the waist segments in some groups of ants.
Spur. Spine-like appendage, may be paired or pectinate, and found at the end of the tibia.
Squamate. Scale-shaped.
Sternal. Pertaining to the sternum or lower portion of the body.
Sternite. The lower sclerite of a segment.
Sting. The modified ovipositer found on female ants at the apex of the gaster, sharp and often ejecting a venomous secretion.
Stria (plural: striae). A fine, impressed line, usually longitudinal in orientation.
Striate. With striae or multiple impressed hairs.
Striate-punctate. Rows of punctures.
Striga (plural: strigae). A narrow, transverse line.
Strigate. Transversely striate.
Subdecumbent. Referring to a hair standing approximately 45 degrees from the body surface.
Suberect. Referring to a hair bending approximately 10 to 20 degrees from vertical.
Subpetiolar process. An anteroventral projection on the petiole or its peduncle, may be absent.
Sulcate. Being deeply furrowed or grooved.
Sulcus. Deep furrow or groove.
Suture. Seam or line that separates two body plates.
Tarsus. A collective term for the five apical segments of any leg.
Tergal. Dorsal.
Tergite. The upper sclerite of a segment.
Thorax. The second major body section, which consists of three body sections: pro-, meso-, and metathorax) In ants and other hymenopterans, the thorax is fused with the first segment of the abdomen, the propodeum. The combined thorax and propodeum form the alitrunk.
Tibia. (plural: tibiae). The fourth segment of the leg found between the femur and the tarsus.
Torulus. The small annular sclerite that surrounds the antennal socket.
Trochanter. The short second segment of the leg, just following the coxa and preceding the femur.
Tubercle. A small, rounded protuberance.
Tubercle. Covered with tubercles (small thick spines).
Venter. The lower surface.
Ventral. The lower surface.
Verrucose. With irregularly shaped lobes or wart-like protuberances.
Vertex. Upper surface of head between eyes, frons, and occiput.
Waist. The isolated body segments between the alitrunk and the gaster, sometimes called the pedicel, but waist is the preferred term.


At times in the keys, various indices and measurements are used. These terms are described below (see the Morphological Measurements page on AntWiki for mor information and diagrams)

Measurements Used

EL - Maximum diameter of compound eye
FL -
Forefemur length
FW -
Forefemur width
longest length of forewing
- Length of gaster in dorsal view (not including acidopore, genitalia of males, or sting)
- Head length in full frontal view from anteriormost point of clypeus to a line perpendicular to the posteriormost point of head.
HW - Maximum width of head (including eyes) in full frontal view
MandL - The straight line length of the mandible at full closure, measured in the same plane for which the HL measurement is taken (i.e. full face view), from the mandibular apex to the anterior clypeal margin, or to the transverse line connecting the anterior-most points in those taxa where the margin is concave medially.
ML (WL) - Mesosomal length (Weber's length) from anterior edge of pronotum to posterior corner of metapleuron
PetNL: Maximum length of petiolar node, measured longitudinally from the level of the anterolateral angle/corner to that of the posterior-most extension of the petiolar tergum, where it surrounds the gastric articulation.
PetW - Maximum width of the petiolar node in dorsal view.
PnL: Pronotal length measured from the anterior edge of the pronotal collar to the pronotal-mesonotal suture parallel to the measuring axis.
PpL: Postpetiole Length. Measured from anterior to posterior inflections of postpetiole node in lateral view.
PpW: Postpetiole width measured as the maximum width of the postpetiole, in same view as and perpendicular to postpetiole length.
PronW (PW) - Maximum width of pronotum
PTH: Petiole Height. Measured from petiole sternum to apex in lateral view.
PTL: Petiole Length. Measured from anterior to posterior inflections of petiole node.
SL - Length of antennal scape from base (not including radical) to terminal point
SPL: Propodeal spine length measured from the tip of propodeal spine to the closest point on outer rim of the propodeal spiracle.
TL - HL + WL + GL


CI = Cephalic index, HW X 100/ HL
FI - Femur index, FL X 100/HL
OI = Ocular index, EL X 100/HL
REL - Relative eye length: EL/HL
REL2 - Relative eye length, using HW: EL/HW
SI = Scape index, SL X 100/HL