Streblognathus

Robertson, H. G., 2002, Revision of the ant genus Streblognathus (Hymenoptera: Formicidae: Ponerinae)., Zootaxa 97, pp. 1-16 : 3-10

Streblognathus Mayr

Streblognathus Mayr 1862: 716.

Type species: Ponera aethiopica F. Smith , 1858, by monotypy.

WORKER (Fig. 1). Large, black, monomorphic ants.

Head (Figs 1a-c). Mandibles elongate with broad angle (about 138°) between apical and basal margin. Apical margin with three teeth followed by three denticles and with a tooth at the basal angle. Inner margin of apical tooth sinuate. Basal margin of mandible with an obtuse angle at about one third of its length from the base. The margin proximal to this angle lies adjacent to the clypeus when mandibles are closed. Mandibles glossy smooth or slightly shagreenate with sparsely distributed punctures containing hairs. Fringe of black or golden hairs inserted on dorsal surface just behind the distal two thirds of the basal margin and the basal tooth, and the hairs extending over the margin into the triangular space between the closed mandibles and the clypeal margin. Also a line of golden hairs along the external margin, and one behind the inner side of the apical margin. Maxillary and labial palps both four segmented. Margin of labrum deeply bisected and fringed with golden hairs (Fig. 1b). Anterior clypeal margin with middle section straight or concave, projecting beyond side margins and meeting them in a right angle or in a tooth-like projection(Fig. 1a). In anterior view, the region between the clypeal teeth is crescent-shaped, shiny, and overhangs the labrum (Fig. 1b). Posterior median portion of clypeus broadly inserted between the frontal lobes and indented medially. Clypeus with sparse, fine golden pubescence and smooth to shagreenate with sparsely distributed punctures containing short, black, pointed subdecumbent hairs that point anteriorly. Frontal triangle prominent between frontal carinae and inlaid into surface of head. Frontal lobes in dorsal view half obscuring the antennal sockets. Frontal carinae short, fading out just behind the level of the anterior margins of the compound eyes. Compound eyes in dorsal view situated at, or slightly anterior to, midlength of head and do not break the lateral margins. Head, excluding mandibles, rounded rectangular, usually a little longer than broad with a flat posterior margin and sides only slightly convex (Fig. 1a). Head covered in fine punctate sculpture, overlaid by fine, sparsely distributed golden pubescence, and covered by short, black, pointed, subdecumbent, curved hairs (Fig. 1c). Punctures poorly defined and unevenly distributed. Antennal scapes bowed, covered in sparse, short, golden or black subdecumbent or decumbent hairs and sparse, fine, golden pubescence. Neck between scape and condylar bulb (radicle) curved strongly downwards. Ventral surface of head smooth to shagreenate with variable densities of golden pubescence and with more-or-less evenly distributed anteriorly pointing, subdecumbent curved hairs.

Mesosoma. In dorsal view, promesonotal suture sharply defined, strongly curved backwards. Metanotal groove slightly impressed, defined in lateral view by the downwardly curving mesonotum meeting the flat propodeal dorsum, although in some specimens the propodeal dorsum curves down slightly at the metanotal groove. In lateral view, propodeum with elongate, flat dorsum and a nearly vertical declivity. Dorsum often with a slight indentation about a quarter of the way from the metanotal groove. Lateral margins of dorsum sometimes distinct posteriorly. At the junction of the dorsum and declivity is a pair of upwardly projecting teeth which are continuous with the sharply raised lateral margins of the declivity (Fig. 1d). Propodeal spiracle slit-shaped. Large metapleural gland opening, fringed with long golden hairs. In many individuals there is a hairless shallow furrow passing from the dorsal edge of the propodeal spiracle, round its posterior edge, and across to above the dorsal edge of the metapleural gland opening. This furrow is reduced to varying degrees across individuals. Mesosoma covered in fine, ill-defined punctate sculpture, smeared to striolate in parts, or appearing shagreenate. Mesosoma covered in sparse, fine, golden pubescence and dorsum with scattered subdecumbent short, black, pointed hairs.

Legs. Middle and hind tibiae each with a pair of pectinate spurs, the posterior spur longer and more pectinate than the anterior. Tarsal claws simple. All legs covered in short subdecumbent hairs.

Petiole (Fig. 1d). Petiolar node with about a third of its height above the level of the propodeal dorsum. In lateral view, anterior and dorsal faces form a single steep convexity that terminates in an acute point where it meets the vertical, concave posterior margin. Dorsum laterally compressed to form an acute, sharp-edged ridge. In dorsal view, petiole node longer than wide and with the posterior point of the dorsum overhanging the posterior face. Subpetiolar process in lateral view with more-or-less horizontal ventral margin meeting posterior margin at an acute but narrowly rounded angle. Petiole unsculptured except for hair pits, covered in sparse, golden pubescence and sometimes with a few strongly curved subdecumbent black hairs.

Gaster. Constriction between first and second gastral segments hardly discernable. Gaster smooth, shiny except for hair pits, and covered in sparse to moderately dense golden pubescence, and sparse black hairs that are bent near their tip. Sting well developed.

MALE (Figs 2-4)

Head (Figs 2a-b). Dominated by the compound eyes which take up 69-75% of the length of the head and which are hemispherical in dorsal view. Ocelli large, hemispherical. Width of median ocellus about the same as the shortest distance between the lateral ocelli. Occipital carina a blade-like ridge. Antennal sockets situated at midlength on the head; diameter of sockets greater than the shortest distance between them and also greater than the distance from outer margin of socket to margin of compound eye. Torulus built up into raised rim round antennal socket. Antennae 13-segmented, elongate, about 83% of total length (from head to tip of gaster). Scape short, equal to or slightly shorter than diameter of median ocellus. Pedicel length slightly shorter than half the length of scape. Flagellum decreases in diameter and length of individual segments from base to tip. Antennae covered in fine, white pubescence. Anterior margin of clypeus built out as a narrow lamella that is broader at the sides than in the middle so that the median anterior margin is concave (Fig. 2b). Tentorial pits deeply impressed (Fig. 2b). Large frontal triangle present above the clypeus and between the antennal sockets. Head smooth with scattered hair pits except for shagreenate sculpture between the antennal sockets and on the frontal triangle and clypeus. Short, sparse golden hairs distributed over head; densest on frontal triangle and clypeus. Vertex reddish brown through to dark brown; golden brown forwards from the anterior margin of the median ocellus.

Mouthparts (Fig. 2b). Mandibles short, rounded, without teeth, not meeting when closed. Labrum bilobed and small, narrower than the distance between the closed mandibles. Maxillary palpi 4-5 segmented, the apical segment being a fusion segment in 4-segmented palpi. One individual had one palp 4-segmented and the other 5-segmented. Labial palpi 3-segmented.

Mesosoma. Pronotum small, vertical, without a dorsal surface; displaced by the large mesoscutum. Median line on mesoscutum fades out at about half its length. Parapsidal lines present, notauli absent. Scutellum dome-like, dorsellum strongly convex in lateral view and slightly overlapping the top of the propodeum. Propodeum gently convex in lateral view and with spiracle slit shaped. Wings as illustrated in Fig. 2c.

Petiole (Fig. 2d). In lateral view, node more-or-less an equilateral triangle with narrowly rounded dorsum. In dorsal view, petiole longer than wide; spiracles on projecting tubercles; shallow ridge along the median line of node. Subpetiolar process with an acute, backwardly projecting spine. Petiole covered in backwardly projecting, slender, pale hairs.

Gaster. Smooth with fine, sparse, golden pubescence. Fifth gastral sternite with a pair of broad lateral ridges with a concavity in between them; long, curved golden hairs along posterior margin. Backwardly projecting golden hairs present on the lateral ridges and shorter less dense hairs in the concavity in between. Subgenital plate narrowing posteriorly and broadly rounded at the apex (Figs 3c-d). Sixth gastral tergite terminates in an acute point.

Genitalia (Figs 3-4). Parameres in cross-section with a sharp-edged dorsal margin and a broadly convex ventral margin. In lateral view, ventral margin of paramere is convex and dorsal margin more-or-less straight. In dorsal view, dorsal margin of paramere is bowed outwards. Exterior and apex of parameres with golden hairs. Volsellae pincer-like: digitus curved outwards and inner margin of cuspidus convex, with a narrow gap between them at their closest point. In lateral view, digitus arches downwards whereas cuspidus is more-orless straight with a broadly rounded apex. Inner surfaces of both digitus and cuspidus covered with small tubercles (Fig. 4). Golden, curved hairs on ventral surface of volsella and inner surface of digitus and cuspidus. Ventral margins of penis valves with large, acute, sharp, backwardly projecting barbs, oriented vertically or outwards, depending on species. Apex of valves splayed outwards or inwards (depending on species) and broadly rounded with backwardly projecting barbs on ventral margin. Dorsal outer edges of penis valves joined by a large trough-like lamella that is V-shaped in cross-section, the whole complex forming the aedeagus.

Diagnosis of Streblognathus

The shape of the petiolar node in the worker, with its sharp-edged dorsal margin and concave posterior face (Fig. 1d) is unique among ants. The shape of the anterior margin of the clypeus is similar to that of Dinoponera in that in both genera there are lateral projections with a concave margin inbetween. However, the projections are acute and spine-like in Dinoponera whereas in Streblognathus they are merely obtuse points or short and tuberculate.

Males in the tribe Ponerini have been insufficiently studied to make a reliable diagnosis for Streblognathus . The large barbs along the ventral margin of the penis valves in Streblognathus are matched by only small serrations in Dinoponera . Dinoponera parameres are elongate linear whereas those in Streblognathus are short and broad. Streblognathus males have a large, acutely angled, subpetiolar process (Fig. 2d) which is absent in Dinoponera .

Key to workers of Streblognathus

1 Scape both absolutely and relatively longer (Scape length 4.32-5.11 mm; Scape index 102-113) (Fig. 5b). Eye length 0.86-1.03 mm; Mesonotal-propodeal length 5.56-6.32 mm; Hind tibia length 4.80-5.54 mm (Figs 5c, e, f)................................. S. aethiopicus

- Scape both absolutely and relatively shorter (Scape length 3.28-4.12 mm; Scape index 87 -98) (Fig. 5b). Eye length 0.62-0.85 mm; Mesonotal-propodeal length 4.34-5.47 mm; Hind tibia length 3.80-4.80 mm (Figs 5c, e, f) .................................... S. peetersi

Key to males of Streblognathus

1 Sides of subgenital plate concave and apex flat (Fig. 3c). Barbed apex of penis valve splayed outwards, whereas barbs along ventral margin oriented vertically (Figs 3a) ... ................................................................................................................... S. aethiopicus

- Sides of subgenital plate convex and apex broadly rounded (Fig. 3d). Barbed apex of penis valve vertical whereas barbs along ventral margin are splayed outwards (Fig. 3b) ........................................................................................................................ S. peetersi