Morphological Terms

(The following text was originally provided by Barry Bolton. We are grateful for his generosity in making it available. It has since been expanded.)

The morphological terms are described here primarily for the worker (ergates) caste. Most of the terms also apply to the queen (gyne) and male (aner), but the specialised terminologies that deal with the sclerites of the pterothorax in alate (winged) forms, venation of the wings themselves, and the male abdomen and male genitalia, are not included. The sclerites of the sting apparatus are described because, although internal in ants, they are ultimately derived from external appendages. Omitted are the names of various forms of sculpture and of minor superficial features of the cuticle. See Surface Sculpturing for details relating to these terms.











Additional Diagrams



Abdomen
The classical third tagma of the insect body. The abdomen in ants consists of ten segments, of which the first seven (AI–AVII) are visible (eight are visible in males). The tergites of segments AI–AVIII each bears a spiracle, which may be exposed or concealed. Segments AVIII and AIX are desclerotised, internal, and form parts of the sting apparatus, so that AVII, because it is always the last visible segment, is usually referred to as being apical. Segment AX is very reduced, at most a simple tergal arc of cuticle, and sometimes vestigial.

The terminologies used to describe the ant abdomen may at first seem confusing. This is because two different systems tend to superimpose, and in places they are not strictly compatible.

(1) A terminology based strictly on morphology, which numbers the visible abdominal segments I–VII, from front to back. This has the clear advantage of indicating homologous segments between different ant taxa, regardless of the specialisations of individual segments or groups of segments in different groups of ants.

(2) A more casual terminology, based on observed subdivisions of the abdominal segments, which names various specialised segments and groups of segments. The advantage here is that the subdivisions are generally easily visible.

The first abdominal segment (AI) is the propodeum, represented only by its tergite (the sternite has been lost), which is immovably fused to the thorax. The body unit formed by the fusion of thorax and propodeum is termed the mesosoma (in some publications called the alitrunk or truncus, or uncommonly and inaccurately just the thorax).

The second abdominal segment (AII) is termed the petiole, and is always specialised. It is usually reduced in size, always separated from the preceding propodeum by a complex narrow articulation, and is usually separted from the following abdominal segments by at least a constriction. In the vast majority of ants the petiole is distinctly isolated both anteriorly and posteriorly.

Abdominal segments II (petiole) to VII (apical) are sometimes collectively called the metasoma (to contrast with the mesosoma = thorax + propodeum). Thus the petiole (AII) may also be referred to as the first metasomal segment, AIII the second metasomal, and so on.

Abdominal segment III (AIII) is termed the first gastral segment when it is full-sized and broadly articulated to the following segment (AIV), but when reduced and distinctly isolated it is commonly called the postpetiole. Abdominal segment III articulates with the preceding petiole by means of the helcium, which itself is formed from the reduced and specialised presclerites of AIII, which fit within the posterior foramen of AII (petiole). The anterior surface of the sternite of AIII may bear a cuticular prora, below the helcium.

The one or two isolated segments that follow the mesosoma may be called the waist. An older term, pedicel, should be abandoned, as it is used universally elsewhere in the Hymenoptera for the first funicular (= second antennal) segment.

Abdominal segment IV (AIV) is the first gastral segment when the waist consists of petiole plus postpetiole, but AIV is the second gastral segment when the waist consists of the petiole alone. Abdominal segments III–VII (when petiole (AII) alone is separated) or AIV–AVII (when petiole and postpetiole (AII + AIII) are separated), are collectively called the gaster, the apparent enlarged “abdomen” that comprises the terminal part of the body.

Each abdominal segment behind the first (propodeum) consists of a pair of sclerites (plates), a dorsal tergite (or tergum) and a ventral sternite (or sternum). These may all be similar, or some may be specialised by reduction, fusion, or subdivision into anterior (presclerite) and posterior (postsclerite) portions that are separated by a constriction (cinctus). Tergites and sternites may be referred to as abdominal or gastral, depending on whether an absolute count, or a count relative to the number of separated waist segments, is used. In workers (and queens), the last visible tergite, that of AVII, is named the pygidium, and its corresponding sternite is the hypopygium. They have individual names because in some groups of ants one or both may be specialised.

Acidopore
The orifice of the formic acid projecting system peculiar to, and diagnostic of, the subfamily Formicinae. The acidopore is formed entirely from the apex of the hypopygium (sternite of AVII). Often it is plainly visible as a short nozzle, generally with a fringe of short setae at its apex. However, in some genera there is no nozzle or setae and the acidopore takes the form of a semicircular to circular emargination or excavation in the apical hypopygial margin. In these taxa the posterior margin of the pygidium may overlap and conceal the acidopore when it is not in use, but the structure is revealed if the pygidium and hypopygium are separated.

The funnel-shaped circlet of hairs around the edge of the acidopore, guarding against back-spray of formic acid, is sometimes called the coronula.

Aculeus
See Sting apparatus.

Alate
Winged (used when referring to queens and occasionally males)

Aliform
Shaped like a wing, approximately wing-like.

Alitrunk
See Mesosoma.

Anapleural sulcus
See Pleurite/pleuron.

Anepisternum
See Pleurite/pleuron.

Annulus
(pl. annuli)

A simple, unsegmented, ring of cuticle. For example, one of the funicular segments of the antenna, or the torulus (= annulus antennalis).

Antenna
(pl. antennae)

The antenna in ants consists of a number of discrete segments (antennomeres; sing. antennomere). These are made up of an elongate basal segment, the scape, that is followed distally by 3–11 shorter segments which together constitute the funiculus (= flagellum), giving a total antennal segment count (= antennomere count) of 4–12. The scape and funiculus meet at an angle so that in life the entire antenna appears bent (geniculate) between the two sections. The basal (first) funicular segment, the one that articulates with the apex of the scape, is sometimes called the pedicel. The scape articulates with the head in the antennal socket (= antennal foramen), a foramen located dorsally on the head, posterior to the clypeus. The funicular segments may all be simple (= filiform), or the segments may gradually enlarge towards the apex (= gradually incrassate), or a number towards the apex may be expanded into a distinctly differentiated clava (= club) that is usually of 2–3 segments but sometimes may be more. When a club is present the antenna is said to be clavate or claviform.

The antennal foramen itself is encircled by a narrow annular sclerite, the torulus (= antennal sclerite), and the socket may be overhung and concealed by the frontal lobe. At the base of the scape is a roughly ball-like condylar bulb (= articulatory bulb, = bulbus), which is the part of the scape that actually articulates within the socket. Just distal of the condylar bulb is a short constriction or neck, which may be straight or curved, distal of which the scape shaft proper commences. The neck and bulb are together referred to as the antennal condyle.

Antennal fossa
(pl. antennal fossae)

The antennal fossa is a depressed area in the cuticle of the dorsum of the head, present in some ant taxa, that surrounds and contains the torulus and antennal socket, which consequently appear to be somewhat sunk into the surface of the head.

Antennal scrobe
(= scrobe, = scrobis)

A longitudinal groove, impression or excavation in the side of the head, which may extend above, below, or in front of the eye, that can accommodate at least the antennal scape but sometimes may accommodate the entire antenna when scape and funiculus are folded together. Scrobes vary in development from simple broad, shallow grooves to extensive deep trenches, but they are absent from the majority of ant genera.

Antennal socket/foramen/insertion
See Antenna.

Antennomere
See Antenna.

Anterior tentorial pits
A pair of endophragmal pits or impressions located anteriorly on the dorsal surface of the head capsule, at or very close to the posterior clypeal margin (epistomal suture). The pits indicate the points of attachment of the anterior arms of the internal skeleton (tentorium) of the head to the head capsule. The termination of the posterior arms of the tentorium are marked by a pair of posterior tentorial pits, which are located close to the occipital foramen.

Apical
At the tip or apex of a structure.

Apophyseal lines
Externally visible lines that mark the internal track of cuticular processes for muscle attachment.

Appressed
Refers to hairs that lie on the body surface, thus parallel, or nearly so, to that surface.

Apterous
Wingless.

Arolium
(pl. arolia)

A median, terminal lobe on the pretarsus (apical tarsomere) of any leg, between the pair of pretarsal claws. Arolia are uncommon in worker ants.

Basal
Situated at or toward the base.

Basitarsal sulcus
A longitudinal groove (sulcus) in the surface of the first (basal) tarsal segment of the leg.

Basitarsus
(pl. basitarsi)

The first, basal, of the five tarsal segments of the leg; the tarsal segment that articulates with the tibia.

See Tarsus.

Buccal cavity
(= oral fossa)

The anteroventral cavity in the head capsule, which contains the labium and maxillae. It is bounded anteriorly by the labrum, posteriorly and laterally by the ventral cuticle of the head (the hypostoma or the genal bridge). Within the buccal cavity the median appendage is the labium, which is flanked by a maxilla on each side of it.

Bulbus
See Antenna.

Bulla
(pl. bullae)

See Pleurite/pleuron.

Calcar
(= spur)

See Tibial spur.

Calyx
See Proventriculus.

Canthellus
See Trulleum.

Cardo
See Maxilla.

Carina
(pl. carinae)

A ridge or low, keel-like crest.

Carinate
Possessing one or more carinae.

Carinula
(pl. carinulae)

Diminutive form of carina.

Cephalic
Pertaining to the head.

Cephalon
See Head.

Cervix
Strictly, the flexible intersegmental region between the head and the prothorax. It is usually shielded from above by a neck-like projection of the anterior pronotum, and from below by fused anterior extensions of the propleuron. Sometimes the anterior portion of the pronotum, that covers and protects the true cervix, is also termed the cervix, or the cervical portion of the pronotum.

Cinctus
See Girdling constriction.

Clava/clavate/claviform (antenna)
With the apical 1-4 funicular segments enlarged and forming a club.

See Antenna.

Claw
SeeTarsus.

Club (antennal)
See Antenna.

Clypeus
Anterior sclerite of the dorsal head, bounded posteriorly by the epistomal suture, which is very commonly referred to as the clypeal suture, or posterior clypeal margin. The median section of the epistomal suture, immediately anterior to the frontal carinae and antennal sockets, is sometimes called the frontoclypeal suture. The anterior clypeal margin usually forms the anterior margin of the head in full-face view (but a projection of the labrum may be anterior to the clypeus in some taxa). The body of the clypeus consists of a pair of lateral portions, or narrow bands of cuticle, on each side of a shield-like median portion. The median portion of the clypeus may be equipped with one or more longitudinal carinae, or may be variously specialised in shape. Posteriorly, the median portion of the clypeus may end in front of the antennal sockets/frontal carinae or lobes, or may project backwards between them. In some taxa the clypeus is extremely reduced and very narrow from front to back, bringing the antennal sockets very close to the anterior margin of the head.

Condylar bulb
See Antenna.

Costate
Covered with a series of close-set ridges that are rounded at their summits.

Coxa
(pl. coxae)

The first, most basal, segment of any leg; the leg segment that articulates within the coxal cavity (= coxal foramen) in the ventral thorax. The coxa of the prothoracic (fore) leg is often termed the procoxa, that of the mesothoracic (middle) leg the mesocoxa, and that of the metathoracic (hind) leg the metacoxa.

Dealate
Refers to the condition of having formerly possessed wings, now shed; also the individual that formerly had wings.

Declivity
See Propodeum.

Decumbent
Refers to a hair or setae inclined at 10-40 degrees from the surface.

Dentate
Possessing teeth, such as the toothed margin of the mandibles.

Denticulate
With many minute teeth.

Diastema
(pl. diastemata)

See Mandibles.

Dimorphic
Within the caste system of an ant colony, the existence of two size classes or subcastes, not connected by intermediates.

Disc
The central portion of a structure such as the clypeus or mesoscutum.

Distal
The farthest part away from the body or the farthest part of a given structure, such as the tip of the wing.

Dorsal
Referring to the dorsum or upper surface; opposite is ventral.

Edentate
Without teeth.

Emarginate
Having a notch, impression, or indentation in a margin, border, or edge.

Endophragmal pit
A pit or pit-like impression in a sclerite that is an external indication of the point of attachment of part of the endoskeleton. Endophragmal pits that are universal in ants include the anterior and posterior tentorial pits, and the mesosternal and metasternal pits. Some groups of ants also have endophragmal pits in other locations.

Endoskeleton
As well as the extensive exoskeleton, ants have a small but significant endoskeleton that consists of sclerotised internal plates that serve as muscle attachments.

The endoskeleton of the head is the tentorium, formed from united anterior and posterior pairs of arms. In ants the fusion is complete and the tentorium takes the form of a pair of longitudinal struts, attached to the head capsule anteriorly and posteriorly. The only visible external indications of the tentorium are the anterior tentorial pits and posterior tentorial pits, which mark the points at which the anterior and posterior tentorial arms attach to the exoskeleton.

The mesothorax has a mesendosternite, derived from the invaginated sternum of the segment. The mesendosternite is a thin, longitudinal, roughly triangular, sclerite that extends the length of the segment and terminates posteriorly at the externally visible mesosternal pit. The dorsum of this sclerite extends into a Y-shaped pair of apodemes that are directed anterolaterally and dorsally, and there may be a reinforcing cross-member between the apodemes.

At the internal junction of the mesothorax and metathorax, just posterior to the mesocoxal cavities, is a raised ridge or low wall of transversely arched cuticle that appears to be derived from the invaginated fused margins of the two segments, right across their line of junction. Arising from the midpoint of this transverse cuticular wall, fused to its vertical midline anteriorly, and extending posteriorly, is the metendosternite. This sclerite is similar in shape to the mesendosternite and terminates posteriorly at the externally visible metasternal pit. The dorsal apodemes of this sclerite may be very long and extend forward into the mesothoracic cavity.

Endosternite
See Endoskeleton.

Epimeral sclerite
(= mesepimeral sclerite, = epimeral lobe)

In some groups of ants there is a small, sometimes detached, posterior lobe of the mesopleuron that covers the orifice of the metathoracic spiracle, which is referred to as the epimeral sclerite (strictly the mesepimeral sclerite) or epimeral lobe. The name is derived from the ancestral morphology of the mesopleuron, where in more generalised forms the pleuron is divided by an oblique suture (the pleural suture) into an anterior mesepisternum and a posterior mesepimeron. No trace of this division remains in ants but, because of the position of the lobe, it is assumed, perhaps incorrectly, to have been derived from the mesepimeron.

Epinotum
An archaic name for the propodeum, used extensively in the past, but only by myrmecologists. Propodeum is the recommended term, because it is universally used elsewhere in hymenopterous morphology, and abandoning epinotum in favour of propodeum brings the terminology of ant morphology into line with the remainder of the Hymenoptera.

Epistomal suture
See Clypeus.

Erect
Refers to a hair that stands straight up, or nearly so, from the body surface.

Ergatogyne
A form that is morphologically intermediate between the worker and queen castes.

Ergatoid
A wingless male reproductive that is worker-like in appearance.

Exocrine gland
A gland whose secretory cells are located below the cuticle but which has pores, ducts, or one or more orifices, that open to the surface.

Facet
An ommatidium, one of the units of the compound eye.

Falcate
Sickle-shaped or saber-shaped.

Femur
(pl. femora)

The third segment of any leg, counting from the basal coxal segment that articulates with the thorax. The femur is generally the longest leg segment and is separated from the coxa only by a small intermediate segment, the trochanter. The femur of the prothoracic (fore) leg is often termed the profemur, that of the mesothoracic (middle) leg the mesofemur, and that of the metathoracic (hind) leg the metafemur.

Fenestra
(pl. fenestrae)

In the sense of the keys presented here, a translucent cuticular thin-spot.

Filiform
(antenna)

With the antennal funiculus thread-like, the segments all of approximately the same width. The contrasting antennal form is clavate (club-like or clubbed), where the apical segments of the antenna are disproportionately enlarged.

Flagellum
(= funiculus)

See Antenna.

Foliaceous (outgrowths)
Small to large roughly leaf-like cuticular projections.

Foramen
(pl. foramina)

A natural opening or perforation in a sclerite. Usually an opening in one sclerite that accommodates the insertion of another. For example, the occipital foramen (= foramen magnum) is the posterior hole in the head capsule within which the articulation with the pronotum is accommodated. Similarly, the the coxal cavities are the ventral foramina within which the coxae articulate with the thorax.

Fossa
A relatively large and deep depression on the body surface.

Fovea
A depression or impressed pit.

Foveate
Body surface covered with foveae.

Foveola
Diminutive of fovea; a small pit or depression.

Frons
The area of the dorsal head posterior to the frontoclypeal suture, above the antennal sockets and including the median ocellus. As ocelli are so often absent in worker ants the posterior limit of the frons can be referred to only in a very vague way in these taxa. Ancestrally, the anterior ocellus arises on the posteriormost part of the frons, while the pair of posterior ocelli arise on the vertex.

Frontal carinae
(sing. frontal carina)

A pair of longitudinal cuticular ridges or flanges on the head, located dorsally behind the clypeus and between the antennal sockets. They are very variable in length and strength of development in the various ant taxa, frequently being short and simple but sometimes extending back to the posterior margin of the head. In some groups the frontal carinae are vestigial or absent, but elsewhere they may be very strongly developed or form the dorsal margins of extensive antennal scrobes. In many groups the frontal carinae anteriorly, especially between the antennal sockets, are expanded into laterally projecting lobate extensions, the frontal lobes, which overhang and partially to entirely conceal the antennal sockets themselves. Frontal lobes may be the only expression of the frontal carinae in some groups. Sometimes the portion of the torulus closest to the cephalic midline is also raised and expanded into a small, laterally projecting, lobe. This may be visible below the frontal lobe, or be fused to the frontal lobe.

Frontal lobes
See Frontal carinae.

Frontal triangle
(= supraclypeal area)

A small, usually triangular patch of cuticle located medio-dorsally on the head, immediately behind the clypeus and approximately between the antennal sockets or the anterior parts of the frontal carinae. Not apparent in many ant taxa and reduced or very narrow in some. In groups where the frontal lobes are medially very closely approximated, the frontal triangle may be compressed and longitudinal, appearing posterior to the frontal lobes as a narrow median sclerite.

Frontoclypeal suture
See Clypeus.

Full-face view
Orientation of the head in which the midpoint of the anterior clypeal margin, the midpoint of the posterior margin, and the midpoints of the sides are in focus at the same time.

Funiculus
(= flagellum)

See Antenna.

Furcula
See Sting apparatus.

Galea
See Maxilla.

Gaster
A useful convenience term for the swollen apical portion of the body that forms the apparent “abdomen”. Morphologically the gaster consists of abdominal segments III–VII when the waist is of a single isolated segment (petiole, = AII), but of abdominal segments IV–VII when the waist is of two isolated segments (petiole plus postpetiole, = AII plus AIII). In the second circumstance, the gaster, when of segments AIV–AVII, may also be termed the opisthogaster.

Gena
(pl. genae)

Area of the side of the head which is bounded in front by the anterior margin of the head capsule, and extends to the posterior margin of the head, below the eye when eyes are present. In ants the gena is expanded ventrally and forms the extensive ventral surface of the head, the genal bridge.

Genal bridge
On the ventral surface of the head the space between the buccal cavity and the occipital foramen is occupied by an extensive area of cuticle, which is divided by a mid-ventral longitudinal line or groove. This surface is formed by the ventral expansion and mid-line fusion of the genae and is called the genal bridge. The extreme anterior margin of the genal bridge, that surrounds the buccal cavity, is the hypostoma.

Geniculate
Bent like a knee joint. The term is usually used to describe the shape of the ant’s antenna in life, where the funiculus is carried at a marked angle to the scape.

Girdling constriction
(= cinctus)

A constriction or sudden and marked narrowing of an abdominal segment, which usually extends around the entire circumference. For convenience it is usually stated in keys that girdling constrictions are present between two segments. This is not strictly correct as the constriction morphologically represents the separation between the presclerites and postsclerites of the more posterior segment. The greater part of the presclerites are usually inserted in the posterior end of the preceding segment and are concealed, leaving only the constriction visible externally.

Glabrous
There are two rather different usages for this term. In the strict sense: refers to a body surface that lacks hairs. In the broad sense the term is commonly to mean smooth and shiny.

Glossa
See Labium.

Gonangulum, gonapophysis, gonocoxa, gonoplac, gonostylus
See Sting apparatus.

Granulopunctate
Refers to a surface that is so finely and densely punctate that it is dull and appears to be made up of tiny granules.

Guard setae
(= guard hairs)

A row or tuft of specialised setae that traverse and protect the orifice of the metapleural gland. These setae usually arise below the orifice of the gland and are directed upward across the orifice.

Gula
Use of this term when referring to the ventral surface of the head capsule in ants is incorrect. Morphologically, the gula is a separated medioventral sclerite of the head, which is bounded anteriorly by the posterior tentorial pits. In consequence the posterior tentorial pits are distant from, and considerably anterior to, the occipital foramen. In ants the posterior tentorial pits are located adjacent to the occipital foramen; no gula sclerite is present.

Head
(= cephalon, = cranium, = prosoma)

The classical first tagma of the insect body. The head capsule is the result of the fusion of six (or perhaps seven) embryonic segments. In adult ants these segments are completely fused and indistinguishable, but most retain appendages that are conspicuous. The appendages of cephalic segment 1 are fused and form the labrum; the appendages of segment 2 are the antennae; the appendages of segment 3 are embryonic only, unrepresented in adults; the appendages of segment 4 are the mandibles, of segment 5 the maxillae, and of segment 6 the labium. Some morphologists argue the presence of a seventh embryonic segment, which would occur between 1 and 3 in the preceding list and bear the eyes as its appendages.

Helcium
The very reduced and specialised presclerites of abdominal segment III, which form a complex articulation within the posterior foramen of the petiole (AII). In general the helcium is mostly or entirely concealed within the posterior foramen of the petiole, but in some groups it is partially visible.

Humerus
(pl. humeri, = humeral angles)

The anterolateral dorsal angle (shoulder) of the pronotum; frequently referred to as humeral angles.

Hypopygium
The sternite of abdominal segment VII; the terminal visible gastral sternite.

Hypostoma
The narrow U-shaped strip of cuticle immediately behind the buccal cavity, that forms its posterior and lateral margins on the anteroventral surface of the head. In ants the hypostoma is often indistinct, sometimes indiscernible, and usually merely forms the anterior margin of the genal bridge, to which it is entirely fused. However, in some taxa a narrow suture remains detectable between the hypostoma and the genal bridge.

Hypostomal teeth
One or more pairs of triangular or rounded teeth that project forward from the hypostoma, towards or slightly into the buccal cavity.

Visibility of the hypostomal tooth depends not only upon its development, but also upon the mandibular configuration as mandibles that shut tightly against the clypeus may impede viewing the hypostomal tooth even if it is of decent size. This tooth may also vary in shape; sometimes straight, sometimes arched. This character can also be studied in ventral view as several taxa have a hypostomal tooth but it is not visible in full-face view.

Katepisternum
See Pleurite/pleuron.

Labial palp
(= labial palpus; pl. labial palpi).

A sensory palp, with a maximum of four segments, that arises anterolaterally on each side of the prementum sclerite of the labium. A count of the number of segments in a maxillary palp and a labial palp, in that order, is called the palp formula.

Labium
With the head in ventral view the labium is a longitudinal appendage, situated medially within the buccal cavity; it is flanked on each side by a maxilla. The labium is formed from an ancestral pair of appendages, now indistinguishably fused together along the midline to form a single structure. The main sclerite of the labium is the prementum. Basal to the prementum, and attaching it to the head capsule, may be a small sclerite, the postmentum, but this area is frequently entirely membranous. The prementum bears a pair of labial palps, one at each side. At the distal end of the prementum is a lobe, the glossa, which may be simple or bilobed apically. The base of the glossa is sometimes flanked by a much smaller lobe on each side, the paraglossa, but in ants these are usually extremely reduced or absent. The glossae and paraglossae together are sometimes termed the ligula.

Labrum
Mouthpart sclerite that hinges on the anterior margin of the clypeus and usually folds back and down over the apices of the maxillae and labium, shielding them when the mouthparts are not in use. In most ants the labrum is a bilobed plate that is not visible in dorsal view, but in some taxa a part of it projects forward from the anterior clypeal margin even when the mouthparts are retracted. Occasionally it is modified into one or more long, prominent labral lobes.

Lacinia
See Maxilla.

Lamella
A thin, plate-like process or ridge, often more or less translucent.

Lancet
See Sting apparatus.

Lateroclypeal tooth
Borowiec (2009) - The modification of the lateral corners of the clypeus, which in cerapachyines can be variably developed, from being bluntly pointed to drawn into conspicuous teeth that project over the mandibles.

Laterotergite
See Tergite/tergum.

Leg segments
(= podites)

Each leg consists of a basal coxa, that articulates with the thorax, followed in order by a small trochanter, a long and generally stout femur, a tibia, and a tarsus. The last consists of five small subsegments (= tarsal segments, = tarsomeres) and terminates apically in a pair of claws on the apical (pretarsal) segment; sometimes there is also a membranous lobe, the arolium, between the claws. The prefixes pro-, meso-, and meta-, applied to any of these terms, indicates that segment on the leg of a particular thoracic segment. For example, mesofemur = the femur of the middle (second) leg; metatibia = the tibia of the hind (third) leg.

Ligula
See Labium.

Malar area
(= malar space)

The area of the head capsule between the base of the mandible and the anterior margin of the eye. Strictly a part of the gena but sometimes its relative length is a useful concept in the taxonomy of some groups.

Mandalus
See Trulleum.

Mandibles
The appendages with which ants manipulate their environment. They are extremely variable in shape, size and dentition, and have great importance in ant taxonomy.

Margins. In full-face view, with the mandibles closed, the longitudinal margin or border of each mandibular blade that is closest to an anterior extension of the midline of the head, is the masticatory margin (= apical margin), and is usually armed with teeth. The base of this margin, close to the anterior margin of the clypeus, usually passes through a basal angle into a transverse or oblique basal margin. The two margins may meet through a broad or narrow curve, or meet in an angle or tooth. When the mandibles are narrow or linear, the distinction between masticatory and basal margins may be lost by obliteration of the basal angle. The external margin (= lateral or outer margin) of each mandible forms its outer border in full-face view and may be straight, sinuate or convex.

In many groups the dorsal base of the body of the mandible bears a number of specialised structures, just distal to the mandibular articulation and proximal of the basal margin of the mandible, the mandalus, canthellus and trulleum; see under ther last named for a discussion of these.

Shape. In the vast majority of ants the mandibular margins form a triangular or subtriangular shape in full-face view, but may be drawn out anteriorly while retaining the basic triangular shape and become elongate-triangular. In several discrete lineages the mandible has become linear; the blade is long and narrow and the external and masticatory margins are approximately parallel or taper gradually to the apex; the whole blade may be straight or curved. Linear mandibles may evolve in one of three ways.

(1) The base of the mandible narrows and the basal angle is obliterated, so that the basal and masticatory margins form a single margin.

(2) The masticatory margin becomes elongated and the basal margin contracted.

(3) The basal margin becomes elongated and the masticatory margin contracted.

Extremely curved mandibles, usually quite short and slender, and with few or no teeth on the masticatory margin, are termed falcate.

Dentition. The masticatory margin of each mandible is usually armed with a series of teeth or denticles (short or very reduced teeth), or a mixture of both, which generally extend the length of the masticatory margin. If teeth alone are present, or a combination of teeth and denticles, the mandible is dentate. If only tiny denticles occur on the margin the mandible is denticulate, and if the margin lacks any form of armament it is edentate. A natural gap in a row of teeth (as opposed to a site where teeth have been broken off or completely worn down) is a diastema (pl. diastemata) and an elongate mandible with an uninterrupted series of teeth may be described as serially dentate. Individual teeth are usually sharp and triangular in shape but may be rounded (crenulate), long, narrow and spine-like (spiniform), or peg-like (paxilliform). Reduced teeth or denticles that occur between full-sized teeth are termed intercalary.

In general the first, distalmost, or apical tooth, the one farthest away from the anterior clypeal margin, is the largest on the masticatory margin, although in some taxa median or even basal teeth may be the largest. The tooth immediately preceding the apical is usually called the preapical tooth (= subapical tooth). Sometimes the term preapical teeth may be loosely applied to all the teeth that precede the apical. The tooth immediately distal of the basal tooth may be termed the prebasal (= subbasal) tooth.

In some genera teeth may also be present on the basal margin of the mandible, but in most this margin is unarmed. Some taxa also have a basal lamella on the mandible. This is a thin cuticular outgrowth from the margin, proximal to any teeth that may be present.

Marginate
Having a sharply defined rim, edge, or margin separating one face of a sclerite, segment, or tagma from another.

Maxilla
(pl. maxillae)

With the head in ventral view the maxillae are situated within the buccal cavity, one on each side of the central labium. The basal segment of the maxilla, that attaches the structure to the head capsule, is the cardo. Attached distally to the cardo is the main sclerite of the maxilla, the stipes, which towards its apex bears a maxillary palp. The inner surface of the stipes bears a lobe towards its distal end, the lacinia, which usually has its free margin irregular, minutely dentiform, or even pectinate. At the distal apex of the stipes is a terminal hood or lobe, the galea, which often folds over the lacinia.

Maxillary palp
(= maxillary palpus; pl. maxillary palpi)

The segmented sensory palp on the maxilla. The palp may have at most 6 segments but these are variously reduced in number in different ant groups; only very rarely are the maxillary palps absent. A count of the number of segments in a maxillary palp and a labial palp, in that order, is called the palp formula.

Mesad
Medially, toward the middle, towards the midline.

Mesendosternite
See Endoskeleton.

Mesepimeron/mesepisternum
See Epimeral sclerite.

Mesonotum
See Tergite/tergum.

Mesopleuron
See Pleurite/pleuron.

Mesosoma
(= alitrunk, = truncus, = apparent “thorax”)

A convenience term for the second visible main section of an ant’s body, following the head. Morphologically the mesosoma consists of the three segments of the true thorax (prothorax, mesothorax, metathorax), to which is fused the propodeum (the tergite of AI), to form a single unit.

Mesosternal pit/Mesosternal process
See Metasternal pit/Metasternal process.

Mesothoracic spiracle
See Spiracle.

Mesothorax
The second segment of the thorax, attached anteriorly to the prothorax, posteriorly to the metathorax, and bearing the mesothoracic (second, median) pair of legs and the first spiracle. The tergite of the mesothorax is the mesonotum. Anteriorly this is attached to the pronotum, either by a mobile suture (promesonotal suture), or by fusion, in which instance the fused nota are termed the promesonotum. Posteriorly the mesonotum is ancestrally attached to the metanotum (tergite of the metathorax), by the mesometanotal suture, but in some ant groups the mesonotum and metanotum are entirely fused. In many ant groups the metanotum is reduced to a transverse groove (metanotal groove), and in some the metanotum is entirely absent. In the last condition the mesonotum posteriorly is attached directly to the propodeum, and if a suture remains between them it is the notopropodeal suture. The fusion sclerite thus produced may be called the notopropodeum. Laterodorsally, the mesonotum abuts the mesopleuron, a long sclerite which extends down to the mesocoxa. Mesonotum and mesopleuron may be separated by a transverse notopleural suture, or the two sclerites may be fused together.

Immediately behind the posterodorsal corner of the mesopleuron there may be a small lobe, or small detached sclerite, the epimeral sclerite (or epimeral lobe), which is probably a detached section of the pleurite. When present it conceals the orifice of the metathoracic spiracle, but this sclerite is absent in many groups (see spiracle).

The mesopleuron may be traversed by a horizontal anapleural sulcus, in which case the portion above the sulcus is the anepisternum, that below the sulcus the katepisternum.

The upper portion of the anterior margin of the mesopleuron abuts the side of the pronotum; below this is a long, free mesopleural margin against which the procoxa rests. Posteriorly, the mesopleuron is fused to the metapleuron by the oblique mesometapleural suture, though in some groups these two sclerites are completely fused and the suture is obliterated.

The ventral surface of the mesothorax consists entirely of the pleurites, which have expanded across to the ventral midline and fused. The ancestral hymenopterous sternite of the mesothorax is internal and represented by the mesendosternite. The anterior margin of the ventral mesothorax often has a projecting median process that extends forward between the bases of the procoxal cavities, and overlaps the posterior margin of the prosternum. On the ventral midline of the mesothorax, anterior to the mesocoxal cavities, is the mesosternal pit, an endophragmal pit that marks the attachment of the mesendosternite to the exoskeleton. This pit is sometimes accompanied by a paired, cuticular, mesosternal process. Immediately posterior to the mesocoxal cavities and the mesosternal pit, is the arched suture that marks the junction of the mesothorax and the metathorax.

Metacoxa
(pl. metacoxae)

The coxa of the metathoracic (= hind, = third) leg. The metacoxae insert posterolaterally in the ventral mesosoma, close to the median emargination in which the petiole articulates. The cavity of this median petiolar articulation may be separated from the cavities in which the metacoxae articulate (metacoxal cavities) by a bar or annulus of cuticle, or the cavities may be confluent. To observe these structures it is necessary to remove the hind legs and mount the ant ventral side uppermost.

Metacoxal cavities
The pair of foramina located posterolaterally in the ventral surface of the metathorax, within which the coxae (basal leg segments) of the metathoracic (hind, third) legs articulate. The metacoxal cavities are located on each side of the usually U-shaped or V-shaped propodeal foramen in which the base of the petiole (AII) articulates. The propodeal foramen may be confluent with the metacoxal cavities on each side, or separated from them by a narrow bar, or a broad annulus, of cuticle.

Metanotal groove/metanotum
A transverse impression or groove separating the mesonotum from the propodeum on the mesosomal dorsum.

See Tergite/tergum.

Metapleural gland
An exocrine gland whose orifice is on the metapleuron, usually situated at or near the posteroventral corner, above the level of the metacoxa and below the level of the propodeal spiracle. The swollen bulla of the metapleural gland is often more conspicuous than the gland’s orifice, and takes the form of a shallow blister or convex swelling on the metapleuron; the bulla sometimes extends almost to the propodeal spiracle. The orifice of the metapleural gland may be a simple pore or hole, or may be protected by cuticular flanges or other outgrowths, or by guard setae that arise below the orifice and extend across it. In a few groups of ants the metapleural gland has been lost.

Metapleural lobe
See Propodeum.

Metapleuron
(pl. metapleura)

See Pleurite/pleuron.

Metasoma
A collective term for abdominal segments II–VII together, regardless of the absence or presence of abdominal constrictions that may occur between any of these segments.

Metasternal pit/Metasternal process
The ventral surfaces of the mesothorax and metathorax each have an endophragmal pit, located on the midline anterior to the level of the coxal cavities. These pits mark the sites of attachment of the endoskeletal mesendosternite and metendosternite to the exoskeleton. In many groups of ants the pits are associated with a pair of cuticular projections, the mesosternal and metasternal processes. In most groups of ants the metasternal pit is distinctly anterior to the apex of the propodeal foramen, but in taxa where the foramen is extensive the pit may be extremely close to its apex.

Metathorax
The third segment of the thorax, attached anteriorly to the mesothorax and dorsally and posteriorly to the propodeum, and bearing the metathoracic (third, hind) pair of legs and usually the second spiracle, though this may be lost in some groups. The tergite of the metathorax is the metanotum. This sclerite is extremely variably developed through the various groups of ants. At its fullest development the metanotum is a distinct transverse sclerite between the mesonotum and propodeum, separated from each by a transverse suture, the mesometanotal suture anteriorly and the notopropodeal suture posteriorly. There is a very common morphoclinal reduction from this condition, which sees the metanotum become gradually shorter, until it is represented only by a narrow transverse groove (metanotal groove), in which the true metanotum is represented only by the exteme base of the groove. In some groups even this groove is obliterated, so that the posterior margin of the mesonotum meets the anterior margin of the propodeum. This junction may be indicated by a feeble transverse impression (notopropodeal suture), or the sclerites may become fully fused, forming a notopropodeum. Conversely, the metanotum may remain present on the dorsum but become indistinguishably fused to the mesonotum, while retaining a strong suture between itself and the propodeum.

Laterally, the metapleuron forms an oblique sclerite that is usually roughly triangular. This is often separated from the mesopleuron by the mesometapleural suture, though in some the two sclerites are completely fused and no trace of a suture remains. Similarly, the dorsal junction of the metapleuron with the propodeum may be indicated by a suture, but again the two may be entirely fused to form a single sclerite, with no trace of a suture between them. Close to the dorsal apex of the metapleuron is the metathoracic spiracle. In groups where the metanotum forms a discrete dorsal sclerite the spiracle is usually located dorsally or laterodorsally, on the side adjacent to the metanotum. Elsewhere, where the metanotum is greatly reduced or absent, the spiracle is lower down on the side. It is sometimes open, sometimes concealed beneath the epimeral sclerite, and in some groups the spiracle has been lost. The posteroventral corner of the metapleuron, above the metacoxa, has the bulla and orifice of the metapleural gland.

The ventral surface of the metathorax consists entirely of the pleurites, which have expanded across to the ventral midline and fused. The ancestral hymenopterous sternite of the metathorax is internal and represented by the metendosternite. The ventral metathorax commences anteriorly in a curved suture immediately posterior to the mesocoxal cavities and mesosternal pit. On the ventral midline of the metathorax, anterior to the metacoxal cavities, is a metasternal pit, an endophragmal pit that marks the attachment of the metendosternite to the exoskeleton. This pit is sometimes accompanied by a paired, cuticular, metasternal process. The metacoxal cavities are located close to the posterior corners of the ventral surface, and the often extensive propodeal foramen, within which the petiole (AII) articulates, extends forward between them.

Metathoracic spiracle
See Spiracle.

Metatibia
The tibial segment of the metathoracic (= hind, = third) leg.

See Leg segments.

Metatibial gland
A presumably exocrine gland that is located on the ventral surface, or more rarely the posterior surface, of the metatibia, usually just proximal of the metatibial spur. When present it varies considerably in shape and size.

Metendosternite
See Endoskeleton.

Mouthparts
The feeding appendages, located anteriorly and anteroventrally on the prognathous head capsule. The mouthparts consist of the mandibles, maxillae and labium, the last two are located within the buccal cavity, on the underside of the head capsule.

Node
A rounded or knob-like structure. Commonly used to refer to the dorsal nodes of the petiole or postpetiole.

In dolichoderine and formicine ants, the petiolar node is referred to as the "scale" when the node is compressed from front to back and is thus rather thin and scale-like when viewed in profile.

Notopropodeal groove
See Tergite/tergum.

Notum
(pl. nota)

The name applied to any one of the three ancestral thoracic tergites. Hence, pronotum is the notum of the prothorax, mesonotum of the mesothorax, and metanotum of the metathorax. In all worker ants each notum is a single sclerite, but in alate forms the mesonotum and metanotum are usually subdivided. As the worker caste is derived ultimately from an alate female caste, the simple nota of the workers represent a secondary reversal to a more generalised condition.

Nuchal carina
A ridge situated posteriorly on the head capsule that separates the dorsal and lateral surfaces (vertex and genae) from the occipital surface.

Oblong plate
See Sting apparatus.

Occipital corners/ margin (of head)
See Posterior corners/margin.

Occipital foramen
(= foramen magnum)

The foramen located posteromedially in the head capsule, within which the membranous cervix articulates the head to the prothorax.

Occiput
(= occipital surface)

The posterior surface of the head capsule, immediately above the occipital foramen. The occiput is usually vertical or nearly so above the foramen, and is separated from the vertex of the cephalic dorsum by the transverse posterior margin of the head capsule.

Ocellus
(pl. ocelli)

A maximum of three simple, single-faceted eyes, which when present (absent in many worker ant taxa) are located in a triangle on the cephalic dorsum. Morphologically the anterior ocellus marks the posterior limit of the frons, and the posterior pair are on the vertex.

Ocular
Pertaining to the eye.

Ommatidium
(pl. ommatidia)

A single optical component (facet) of the compound eye.

Opisthogaster
See Gaster.

Palp Formula
(PF)

A standardised way of indicating the number of segments in the maxillary and labial palps. The number of maxillary palp segments is given first, the number of labial palp segments second. Thus PF 6,4 indicates that the maxillary palp has six segments, the labial palp four.

Parafrontal ridges
Borowiec (2009) - derived from Wilson’s (1964) work on Aenictus, and is used for low lines running from lateral portions of clypeus laterad to antennal sockets, thus separating them from the genae. Such ridges are present in most Cerapachyini, but absent in many Sphinctomyrmex, all Acanthostichus and Cylindromyrmex.

Paraglossa
See Labium.

Parapsidal furrow
Most hymenopterists regard notauli (=notaulices) as the Y-shaped groove in the middle of the scutum, while the parapsidal furrows are more lateral, usually parallel grooves. Most ant workers called the notauli "Mayrian furrows" before about 1950.

Pectinate
Comb-like or bearing a comb.

Pedicel
An archaic term used in ants for the isolated body segments between mesosoma and gaster, namely the petiole (AII), or petiole plus postpetiole (AII plus AIII). Use of the term pedicel is no longer recommended in this sense, as it is used elsewhere throughout the Hymenoptera as the name for the first funicular segment of the antenna. Abandonment of pedicel as a name for part of the abdomen brings ant morphological terminology into line with the remainder of the Hymenoptera.

Peduncle
(of petiole, = AII)

The relatively slender anterior section of the petiole which begins immediately posterior to the propodeal-petiolar articulation and extends back to the petiolar node or scale. It is very variable in length and thickness, but when present in any form the petiole is termed pedunculate. When a peduncle is absent, so that the node or scale of the petiole immediately follows the articulation with the propodeum, the petiole is termed sessile. If an extremely short or poorly defined peduncle occurs, the petiole is termed subsessile.

Petiole
(= abdominal segment II (AII), = first metasomal segment)

Morphologically the second abdominal segment (AII), the segment that immediately follows the mesosoma. Anteriorly, it is always articulated within the propodeal foramen of the mesosoma. Generally the petiole takes the form of a node (nodiform) or of a scale (squamiform) of varying shape and size, but in some taxa it may be very reduced, represented only by a narrow subcylindrical segment that may be overhung from behind by the gaster. The petiole bears the second abdominal spiracle and usually consists of a distinct tergite and much smaller sternite. The tergite may have a differentiated laterotergite, low down on each side and abutting the sternite. The sternite often has a specialised, depressed area anteroventrally, close behind the articulation, that is equipped with numerous, short sensory hairs: the proprioceptor zone. In some groups the tergite and sternite of the petiole are fused together (tergosternal fusion).

Pilosity
The longer, stouter hairs or setae, which stand out above the shorter and finer hairs constituting the pubescence.

Plectrum
See Stridulatory system.

Pleurite/pleuron
(pl. pleura)

The lateral sclerites of the thorax proper, excluding the propodeum which is morphologically the tergite of the first abdominal segment. The propleuron (pleuron of the prothorax) is relatively small in ants and is mostly or entirely overlapped and concealed by the lateral part of the pronotum when viewed in profile, but can always be seen clearly in ventral view (see prothorax). The mesopleuron (pleuron of the mesothorax) is the largest pleurite. It may consist of a single sclerite that extends almost the entire height of the lateral mesothorax or may be divided by a transverse sulcus (the anapleural sulcus) into an upper anepisternum and a lower katepisternum (see mesothorax). The metapleuron (pleuron of the metathorax) is located posteriorly on the side of the mesosoma, below the level of the propodeum. The metapleuron bears, in almost all ants, the metapleural gland (see metathorax). The ventral surfaces of the mesothorax and metathorax are formed by the ventral expansion of the pleurites and their fusion along the ventral midline; the true sternites of these segments are represented only by endoskeletal structures. The abdominal segments do not have pleurites and each consists only of tergite (above) and sternite (below).

Podites
See Leg segments.

Posterior tentorial pits
See Anterior tentorial pits.

Postmentum
See Labium.

Postpetiole
(= abdominal segment III (AIII))

A convenience term for what is morphologically the third abdominal segment when it is reduced in size and markedly separated from the petiole (AII) anterior to it and from the fourth abdominal segment (AIV) posterior to it.

Posterior corners/margin (of head)
With the head in full-face view, the rounded to acute posterolateral angles, where the sides of the head curve into the posterior margin; the latter extends transversely between the corners. Earlier frequently referred to as occipital corners and occipital margin, these terms are not strictly accurate because the true occipital surface (occiput) is not involved.

Postsclerite/poststernite/posttergite
See Presclerite.

Prementum
See Labium.

Presclerite
A distinctly differentiated anterior section of an abdominal sclerite (tergite or sternite) that is separated from the remaining posterior portion of the sclerite by a ridge, constriction, or both. In abdominal segments III–VII it is usual for the posterior portion of each segment to overlap the anterior portion of the following segment. The overlapped area usually lacks sculpture and pilosity, but the absence of these features alone does not constitute a presclerite: there must be a constriction or ridge that separates the two zones. Presclerites derived from tergites are termed pretergites; those from sternites, presternites. The remainder of each sclerite, posterior to the constriction or ridge, is the postsclerite, posttergite dorsally and poststernite ventrally. A marked constriction that separates presclerites from postsclerites and extends around the entire circumference of a segment is a girdling constriction (= cinctus). The presclerites of abdominal segment III are reduced and form a specialised articulation within the posterior foramen of segment AII (petiole), the helcium.

Presternite/Pretergite
See Presclerite.

Pretarsus/Pretarsal claws
(= ungues, sing. unguis)

See Tarsus.

Profile
Orientation of part of the body (usually the mesosoma) in side (lateral) view so that the anterior, posterior, dorsal, and ventral outlines are in focus at the same time.

Prognathous (head)
Among the ants the long axis of the head is horizontal or nearly horizontal, so that the head more or less continues the line of the long axis of the body, and the mouthparts, particularly the mandibles, are at the front of the head capsule. The ventral surface of the head has an extensive cuticular area (genal bridge) that widely separates the buccal cavity from the occipital foramen. This prognathous condition is in marked contrast to almost all the other families of Hymenoptera, where the long axis of the head is vertical or nearly vertical, the mandibles are ventral, and the buccal cavity and occipital foramen are closely approximated or even confluent; a condition termed hypognathous.

Because of the prognathous condition of the head, references to its orientation differ from what is usual in Hymenoptera. Apart from the mandibles being anterior, what is referred to as the frontal or anterior surface of the head elsewhere in the order, is dorsal in ants.

Promesonotal suture
The transverse suture across the dorsal mesosoma and down its sides, that separates the pronotum from the mesothorax. In many groups of ants the promesonotal suture is fully developed, articulated and flexible. The posterior margin of the pronotum slightly overlaps the anterior mesonotum and the two sclerites are linked by intersegmental membrane so that they are capable of movement relative to each other. Elsewhere, and very commonly, the suture is reduced from this condition. Initially in the sequence of reduction the suture is still present and distinct but inflexible, as the posterior pronotal margin has fused to the anterior margin of the mesonotum, and the intersegmental membrane has been lost. Beyond this fused condition the suture shows a gradual morphoclinal reduction in size and degree of definition, eventually becoming nothing more than a faint line or weak impression across the dorsum, or often disappearing altogether. When fusion and obliteration of the suture is advanced, and there is little or no sign of separation of the two original sclerites, the resultant fusion sclerite is termed the promesonotum.

Promesonotum
The pronotum and mesonotum are sometimes fused to form one structure called the promesonotum.

See Promesonotal suture.

Pronotum
The first (anterior) tergite on the mesosomal dorsum.

See Tergite/tergum.

Propodeal lobe
(= metapleural lobe, = inferior propodeal plate)

See Propodeum.

Propodeal spiracle
See Propodeum.

Propodeum
Morphologically, the tergite of the first abdominal segment (the sternite of which is lost). It is immovably fused to the thorax and forms most of the posterior section of the mesosoma (= alitrunk). An older term for this sclerite, epinotum should be abandoned.

The propodeal dorsum, which is sometimes referred to as its basal surface or base, is usually unspecialised but frequently terminates posteriorly in a pair of teeth or spines. The sloping posterior surface is the propodeal declivity, and may bear a number of specialisations. Most common of these is the development of a pair of propodeal lobes (= inferior propodeal plates). When present these are situated at the base of the propodeal declivity, one on each side of the propodeal foramen, the posterior foramen of the mesosoma within which the petiole (AII) articulates. These lobes, which when present may vary considerably in shape and size, were frequently referred to as metapleural lobes in earlier publications, but this name should be abandoned as the lobes are morphologically part of the propodeum, not the metapleuron.

The side of the propodeum bears the propodeal spiracle, morphologically the first abdominal spiracle. Its shape, size and location are variable and of considerable taxonomic value.

Prora
(pl. prorae)

A cuticular process or prominence that projects forward from the anterior surface of abdominal sternite III, below the helcium. Absent in many groups; when present it takes the form of a U-shaped ridge of cuticle, a tubercle of very variable size, or a distinct prow. In some specialised taxa the prora has become inserted between the tergal apices of the helcium and forms part of the articulation.

Prosoma
See Head.

Prosternite
See Sternite/sternum.

Prothorax
The first of the three segments of the thorax, articulated anteriorly to the head by the membranous cervix, attached posteriorly to the mesothorax, and bearing the prothoracic (first, anterior) pair of legs. In worker ants the tergite of the prothorax is the hypertrophied pronotum, that extends across the dorsum and down both sides of the segment, and also extends for some distance medially on the ventral surface, behind the procoxal cavities, where it overlaps or fuses with the anterior margin of the ventral mesothorax. The posterior margin of the lateral portion of the pronotum usually covers and conceals the mesonotal spiracle. The pleurites of the prothorax are only partly visible in profile as they are largely concealed by the lateral parts of the pronotum (a condition termed cryptopleury), but the pleurites are always conspicuous in ventral view. They are fused along the ventral midline, but laterally are movably articulated to the pronotum, so that the two propleurites move as a single unit. Mid-ventrally, between the procoxal cavities and posterior to the pleurites, is a small, usually shield-like sternite (prosternum), the posterior margin of which may be overlapped by an anteriorly projecting medioventral process of the mesothorax. The procoxal cavity is complex, being bounded anteriorly by the propleurite, medially by the prosternite, laterally by the pronotum, and posteriorly by the pronotum and anterior mesothorax. The pronotum articulates with the mesonotum at the promesonotal suture. This may be entirely flexible, with the two sclerites linked by intersegmental membrane, or the pronotum may be completely fused to the mesonotum, producing a compound sclerite, the promesonotum. The prothorax does not have a spiracle or an endoskeletal sclerite.

Proventriculus
A muscular pump located in the intestine between the crop and the midgut. In all ants the proventriculus has a basal bulb, but in some the bulb is surmounted by a ring of four sclerotised sepals, collectively termed the calyx. Although an internal abdominal structure, the form of the proventriculus featured strongly in the early classifications of some subfamilies, so is included here.

Psammophore
A basket-like series of long, and usually stout, curved setae that arise from the ventral surfaces of the head and mandibles in some deserticolous ants, used for carrying sand grains. In some publications the setae of the psammophore are called ammochaete hairs.

Pubescence
The very fine, short hairs that usually form a second layer beneath the longer, coarser pilosity. The pubescence is commonly appressed, less commonly it is suberect.

Pygidium
The tergite of abdominal segment VII; the terminal visible tergite of the abdomen.

Quadrate plate
See Sting apparatus.

Recumbent
Refers to a hair lying on the body surface.

Ruga
(pl. rugae)

A wrinkle on the body surface.

Rugose
Refers to a surface with multiple rugae that are approximately parallel.

Rugoreticulate
Refers to a surface with irregular, coarse rugae that form a coarse network. Differs from reticulate only by being coarser and more irregular.

Rugosopunctate
Refers to a surface that is so coarsely and densely punctate that the raised areas between the punctures are narrow and ruga-like in appearance. This surface texture grades to reticulorugose.

Scape
The first antennal segment, articulated to the head via the antennal socket. In female ants, this segment is enormously elongate in comparison to the succeeding segments of the antenna.

See Antenna.

Sclerite
Functionally, a general term for any single plate of the exoskeleton (e.g. pronotal sclerite, abdominal sclerites); more specifically, an integumental plate in which the protein sclerotin has been deposited. In the case of ants, the latter applies to all parts of the exoskeleton.

Scrobe/scrobis
A deep groove, often marginate, into which an appendage may be folded.

See Antennal scrobe.

Sepals
See Proventriculus.

Serrate
Bearing fine teeth along the edge, similar to a saw-blade.

Sessile (petiole)
See Peduncle.

Seta
(pl. setae)

Any stout hair-like cuticular process that is socketed basally. Generally, as here, the terms seta and hair are interchangeable, but care must be taken to differentiate between setae and pubescence, as the latter may also sometimes be referred to as hairs.

Shagreened
Refers to a surface covered with fine, close-set roughness, similar to a shark-skin.

Spiracle
An orifice of the tracheal system by which gasses enter and leave the body. Adult ants have 9 or 10 spiracles on each side of the body. The spiracles of the prothorax have been lost, so the first spiracular opening occurs on the mesothorax. This mesothoracic spiracle is situated forward and quite high on the side of the segment and is usually concealed from view by a backward-projecting lobe of the pronotum; only rarely is its orifice open and clearly visible. The metathoracic spiracle may be dorsal (especially when the metanotum forms part of the dorsal mesosoma), lateral and open, lateral but concealed by a small, sometimes detached, lobe of the mesopleuron (the epimeral sclerite); or the metathoracic spiracle may be absent. Abdominal spiracles are always on the tergite of each segment. The propodeal (first abdominal) spiracle is usually the largest on the body. Behind this, on the metasoma (AII to apex), spiracles are always visible on abdominal segments II–IV, but those on abdominal segments V–VII are frequently overlapped and concealed by the posterior margin of the preceding tergite. A spiracle is also present on abdominal tergite VIII, but this sclerite is always concealed; it is internal and forms part of the sting apparatus (the spiracular plate).

Spiracular plate
See Sting apparatus.

Spongiform (tissue)
Specialized sponge-like external cuticular tissue, distributed mainly about the waist segments in some groups of ants.

Spur
(= calcar)

A spine-like appendage at the apex of the tibia; often paired.

See Tibial spur.

Spur formula
A simple statement of the number of tibial spurs that are present on the pro-, meso-, and metathoracic legs, given in that order. Thus a spur formula of 1, 2, 2, indictaes that the tibia of the prothoracic (fore) leg has one spur, that of the mesothoracic (middle) and metathoracic (hind) legs each have two spurs.

Squamate
Refers to a broad, flattened, scale-like hair.

Squamiform
In the form of a scale.

Sternite/sternum
(pl. sterna)

The lower or ventral sclerite of a segment (the tergite is the upper sclerite on the thoracic segments and the abdomen; the pleurites are the lateral sclerites on the sides of the thorax). The sternite may be a simple, flat or curved plate, or may be specialised or subdivided on some segments. On the prothorax the sternite (prosternum) is small, but visible in ventral view (see prothorax). The sternites of the mesothorax and metathorax are internal (mesendosternite and metendosternite, respectively), the ventral surfaces of these two segments being composed of extensions of the pleurites to the ventral midline, where they fuse (see mesothorax and metathorax). The sternite of the propodeum (AI) has been lost in the course of evolution, but those of the remaining visible abdominal segments (AII–AVII) are usually distinct, although the lateral margins of some may be difficult to discern because of fusion to the tergite (tergosternal fusion). The sternites of AVIII and AIX are membranous, internal, and associated with the sting apparatus. Abdominal sternites are usually simple, but may be subdivided or otherwise specialised. The most common modification applies to abdominal sternites III and IV (uncommonly also to AV and AVI), where distinct presternites (see under presclerites) may be differentiated.

Sting apparatus
(= aculeus)

Internal in workers (and queens) of the ant subfamilies in which it occurs, concealed within the apical visible segments of the abdomen. The sting apparatus is derived from parts of the ancestral exoskeleton of abdominal segments VIII and IX, subtended by a number of pairs of sclerites that are ultimately derived from the ancestral coxal homologues of those segments; one pair from segment AVIII and two pairs from segment AIX. Most sclerites of the sting apparatus have accumulated a number of synonymous names, as follows.


 * Gonangulum (= first valvifer, = triangular plate).
 * Gonapophysis VIII (= first gonapophysis, = first valvula, = lancet).
 * Gonapophysis IX (= second gonapophysis, = second valvula, = stylet).
 * Gonocoxa IX (= second valvifer, = second gonocoxa, = oblong plate).
 * Gonoplac (= third valvula, = gonostylus, = sting sheath).
 * Sternites AVIII and AIX are membranous and usually inconspicuous.
 * Tergite AVIII (= spiracular plate); frequently split into a pair of hemitergites, one on each side.
 * Tergite AIX (= quadrate plate); always split into a pair of hemitergites, one on each side.

The most ventral sclerites of the apparatus are the longitudinal pair of gonapophyses VIII. These are attached to the base (anterior end) of the apparatus and curve posteriorly then upward, where they meet and lock with the pair of gonapophyses IX, the next sclerites dorsally. The latter are fused along their length and form the upper portion of the channel through which venom is transmitted; the lower portion of this channel consists of the pair of gonapophyses VIII. All these sclerites together are sometimes termed the terebra. The bases of gonapophyses IX arise directly from the bases of the next sclerites dorsally, gonocoxae IX, whose length is extended by the gonoplacs, which arise directly from the apex of each gonocoxa IX and continue its line. Gonapophyses VIII are attached basally to a pair of roughly triangular gonangula, which also articulate with the bases of gonocoxae IX. The gonangula articulate on each side with the bases of the hemitergites of AIX, which extend posterodorsally. This entire system is covered from above by the arc of tergite AVIII, which bears the terminal abdominal spiracle. A final small sclerite, visible in some groups, is the furcula. This is a small, inverted Y-shaped sclerite at the extreme base of the sting apparatus; its arms are attached to the gonapophyses, from which it has probably been derived.

In two large subfamilies this complex venom-injecting apparatus has been abandoned in favour of repugnatorial glands or a formic acid projection system. However, dissection of these highly modified forms reveals some remnants of the original sting apparatus, here adapted to different, usually supportive, functions.

Sting sheath
See Sting apparatus.

Stipes
(pl. stipites)

See Maxilla.

Stria
A fine impressed line on the body surface; usually many striae occur together, resulting in a striate surface.

Stridulatory system
A sound-producing system present in a number of ant subfamilies. The system consists of a plectrum (= stridulatory file), located on the posterior margin of abdominal segment III (usually, but not always, on the tergite), and an extremely finely grooved stridulitrum on the anterior portion of abdominal segment IV. Rapid to-and-fro movement of the plectrum along the stridulitrum produces a range of chirping or buzzing sounds.

Stridulitrum
See Stridulatory system.

Strigil
See Tibial spur.

Stylet
See Sting apparatus.

Suberect
Refers to a hair that stands at an angle of about 45° from the body surface.

Subpetiolar process
A ventral cuticular projection of the sternite of the petiole (AII), either below the node or on its anterior peduncle; sometimes absent but when present very variable in shape and size.

Subsessile (petiole)
See Peduncle.

Sulcus
(pl. sulci)

Strictly, an external groove or impression that corresponds to an internal ridge-like inflection of the cuticle, which provides mechanical rigidity. The term is also casually used for any linear impression in the cuticle, without any obvious significance, and sulcus is often used interchangeably with suture.

Suture
Strictly, a line of junction between two structural sclerites. The suture may be articulated, where the component sclerites are linked by flexible intersegmental membrane and retain the ability to move relative to each other, or may be fused together and immobile. The term suture is often used interchangeably with sulcus.

Supraclypeal area
See Frontal triangle.

Tagma
(pl. tagmata)

A fundamental unit of the body; an ancestral section of the body that is distinct from, or separated from, other body units in both form and function. In Insecta there are three ancestral tagmata: head, thorax and abdomen, but in ants the second and third of these have become much modified by secondary evolutionary developments.

Tarsal claws
See Tarsus.

Tarsus
(pl. tarsi)

Collective term for the five small apical subsegments (tarsomeres) of any leg. The first tarsal segment (first tarsomere, basal tarsomere) of each leg articulates with the tibia and is termed the basitarsus. The next three tarsomeres are not individually named but the fifth, apical (terminal) tarsomere is the pretarsus and bears a pair of pretarsal claws (= ungues, sing. unguis). The inner curvature of each claw may be a simple, smooth, concave surface, or may have one or more preapical teeth present, or the claw may be pectinate. Occasionally a membranous lobe, the arolium, may be present between the claws. The tarsus of the prothoracic (fore) leg is often termed the protarsus, that of the mesothoracic (middle) leg the mesotarsus, and that of the metathoracic (hind) leg the metatarsus. The individually named tarsomeres may be referred to in a similar way, for instance the basitarus of the prothoracic (fore), mesothoracic (middle), and metathoracic (hind) legs may be termed probasitarsus, mesobasitarsus and metabasitarsus, respectively. In some groups of ants the metabasitarsus bears a longitudinal groove that is probably the orifice of an exocrine gland.

Tentorium
See Endoskeleton.

Tergite/tergum
(pl. terga)

The upper sclerite of a segment (the sternite is the lower, the pleurite the lateral on the thorax). The tergite may be a simple flat or curved plate, or may be specialised or subdivided on some segments. In terms of comparative morphology each of the three ancestral dorsal plates of the thorax, one for each segment, is termed the notum (pl. nota). Thus, the tergite of the prothorax is composed entirely of the pronotum. This sclerite is hypertrophied in worker ants and extends across the dorsum and down both sides of the segment, mostly or entirely concealing the propleuron (see prothorax). The mesonotum, tergite of the mesothorax, may be separated from the pronotum by the promesonotal suture, or the pronotum and mesonotum may be fused by obliteration of the suture, to form a single sclerite, the promesonotum (see mesothorax). The metanotum, tergite of the metathorax, may be present on the dorsum as a distinct sclerite, but is frequently reduced and sometimes entirely lost. When the metanotum is extremely reduced, the mesonotum and propodeum are only separated by the metanotal groove (= notopropodeal groove), a transverse impression whose base represents the very last vestige of the metanotum on the dorsum (see metathorax). The propodeum is the tergite of the first abdominal segment (AI). The remaining visible abdominal segments (AII–AVII) have tergites that are usually simple, but may be subdivided or otherwise specialised. The most common modification applies to abdominal tergites III and IV (uncommonly also to AV and AVI), where distinct pretergites and posttergites (see under presclerites) may be differentiated. In general the abdominal tergites are free and attached to their respective sternites by flexible intersegmental membrane, but in some groups there is tergosternal fusion in segments AII (petiole), AIII and AIV. The petiole (AII) in some groups has a small lower section of the tergite split off from the main part of the sclerite by a distinct suture, on each side, where they flank the sternite. These are called laterotergites, and in some taxa these sections of the tergite are mobile, with repect to both the remainder of the tergite and also the sternite.

Tergosternal fusion
A condition of the abdominal segments where the tergite and sternite of a single segment fuse together. This may occur in some or all abdominal segments from AII (petiole) to AIV.

Thorax
The classical second tagma of the insect body. In ants and other Hymenoptera the apparent thorax consists of the usual three leg-bearing body segments of the true thorax (prothorax, mesothorax, metathorax, each discussed separately), to which the tergite of the first abdominal segment (the propodeum) is immovably fused. This modification means that the combined “true thorax + propodeum” cannot strictly be called the thorax, as it is not homologous with the term as used otherwise throughout the Insecta. Several names have been utilised in the recent past for “true thorax + propodeum”, of which three, mesosoma, alitrunk and truncus have been frequent. All three names are somewhat misleading as far as the ants are concerned, but they are all improvements over “thorax”, which is morphologically inaccurate. Currently the term mesosoma has gained ascendency, and is the name recommended here.

Tibia
(pl. tibiae)

The fourth segment of any leg, counting from the basal segment (coxa) that articulates with the thorax. At its apex the tibia frequently bears one or two tibial spurs. The tibia of the prothoracic (fore) leg is often termed the protibia, that of the mesothoracic (middle) leg the mesotibia, and that of the metathoracic (hind) leg the metatibia.

Tibial spur
(= calcar)

One or two basally socketed spurs, located at the apex of each tibia. The forelegs (prothoracic legs) have a single pectinate tibial spur that is modified as part of a specialised antennal cleaning device, the strigil. The mesothoracic (middle) and metathoracic (hind) tibia, also referred to as mesotibia and metatibia, may each have two, one or no spurs present. When present the mesotibial and metatibial spurs may be pectinate, barbed, or simple cuticular spikes. If two spurs are present on a tibia it is usual for one to be larger then the other, and in such instances the larger spur is often pectinate, while the smaller spur is simple. A simple count of the number of tibial spurs on each of the three legs, from front to back, is the spur formula.

Torulus
(= antennal sclerite, = annulus antennalis)

The small annular sclerite that surrounds the antennal socket (antennal foramen). The torulus may be horizontal, or the part closest to the midline of the head may be elevated, in some taxa to such an extent that the antennal socket is almost vertical. The upper arc of the torulus may be indistinguishably fused to the inner wall of the frontal carina, or may remain discrete, or may even project laterally as a small torular lobe below the frontal carina. In some groups where the frontal carina is very slender, the torulus projects laterally beyond the outer margin of the frontal carina, and becomes visible in full-face view.

Triangular plate
See Sting apparatus.

Trochanter
The second segment, counting from the base, of any leg; the small segment between the coxa and femur. In all recent ants the trochanter is a single segment, but it represents the result of fusion of an ancestral pair of small segments. The trochanter of the prothoracic (fore) leg is often termed the protrochanter, that of the mesothoracic (middle) leg the mesotrochanter, and that of the metathoracic (hind) leg the metatrochanter.

Trulleum
A basin-shaped depression near the dorsal base of the mandible, close to its articulation. It is bounded distally by the basal margin of the mandibular blade and, in those groups where it occurs, is visible just in front of the anterior clypeal margin when the mandibles are open. The trulleum in many groups is closed along its inner (medial) border by a raised ridge of cuticle, the canthellus. The canthellus may extend to, and even fuse with, the basal margin of the mandible (canthellus closed), or may fail to reach the basal margin (canthellus open). Proximal to both these structures, in the cuticle of the extreme dorsal base of the mandible, is a small, unsclerotised impression of variable shape, the mandalus. It contrasts strongly with the fully sclerotised surrounding cuticle of the mandibular base.

Tubercle
A small, rounded prominence or protuberance; short, thick, usually blunt, spines or pimple-like structures.

Tuberculate
Bearing one or more tubercles.

Tuberculiform
Having the form or appearance or a tubercle.

Tumulus
(pl. tumuli)

A prominent, small, mound-like or rounded hill-like to subconical, but not acutely pointed, cuticular excrescence.

Unguis
See Tarsus.

Valvifer, valvula
See Sting apparatus.

Ventral
Refers to the lower surface.

Vertex
The portion of the cephalic dorsum that lies immediately in front of the occiput. In those groups where ocelli are absent the area can be only vaguely defined, but in those which possess ocelli the vertex is the area from immediately behind the anterior ocellus to the occiput, that contains the posterior pair of ocelli. Ancestrally, the anterior ocellus is on, and marks the posterior limit of, the frons.

Waist
An informal collective term for the one or two isolated and reduced abdominal segments that occur between the mesosoma and gaster. When only the petiole (AII) is isolated the waist is said to be one-segmented, but in those taxa where the postpetiole (AIII) is also separated the waist is said to be two-segmented.