Tropidomyrmex, Silva, Rogério R., Feitosa, Rodrigo M., Brandão, Carlos Roberto F. & Diniz, Jorge L. M., 2009

Silva, Rogério R., Feitosa, Rodrigo M., Brandão, Carlos Roberto F. & Diniz, Jorge L. M., 2009, Tropidomyrmex elianae, a new myrmicine ant genus and species from Brazil, tentatively assigned to Solenopsidini (Hymenoptera, Formicidae), Zootaxa 2052, pp. 32-48 : 34-38

Tropidomyrmex gen. n.

( Figs. 1–11 )

Type species: Tropidomyrmex elianae sp. n., by present designation.

Worker. Monomorphic myrmicine ants. Size relatively small (TL 2.15–2.57). Body color pale-yellowish, with appendages somewhat lighter. Integument extremely thin, predominantly smooth and rather opaque, with the inferior portions of meso- and metapleuron finely striate. Pilosity composed mainly of short to long, flexuous, suberect hairs.

Head subquadrate, in full face view; lateral borders and dorsal surface slightly convex; vertexal margin strongly concave medially; posterolateral corners rounded. Mandibles narrow, weakly convex dorsally, and with external margins considerably curved inwards; masticatory margins very short and mostly edentate, except for the apical tooth which is extremely developed. Palpal formula 1,2. Maxillae stipes without transverse crest. Clypeus very broad and convex dorsally, posteriorly emarginate; lateral portions set lower than central disc; anterior margin very pronounced anteriorly at the median portion. Frontal lobes very reduced, exposing the antennal insertions. Toruli visible in full-face view, their maximum exposure anterior to point of maximum width of frontal lobes. Frontal triangle indistinct. Compound eyes relatively small, occupying some 5% of the head capsule, and set at the same level as the surrounding surface of head. Antennae 11-segmented, segments gradually increasing in size without a noticeable club; apical segment as long as the four preceding ones; antennal condyle exposed; scapes with dorsal surface convex apically and failing to reach the vertexal margin.

Mesosoma compact; pronotum relatively large; promesonotal suture distinct under SEM ( Fig. 10 C); propleuron well developed; dorsal surface of mesonotum separated from anepisternum by a distinct suture; metanotal suture vestigial; propodeum unarmed and with the dorsal surface strongly sloped posteriorly, propodeal spiracle relatively large, posterior declivity strongly concave, so that it can receive the entire petiole when it is closed against the mesosoma, propodeal lobes reduced, not visible in side view. Legs relatively short and robust, middle and hind tibiae without apical spurs; tarsal claws simple.

Petiolar peduncle short, without a ventral carina or processes, node distinct, high, and dorsally convex in profile; postpetiole broader than long in dorsal view and relatively narrow in lateral view, ventral process well developed, as broad as postpetiole, and formed by two divergent lobes, when seen in ventral view. Gaster moderately elongate, with the first segment (IV abdominal) larger than the posterior ones; tergite of abdominal segment IV (first gastral) broadly overlapping sternite on ventral surface of gaster; gastral shoulder inconspicuous.

Sting apparatus. Spiracular plate subrectangular; dorsal notch absent; spiracle relatively wide; anterior apodeme narrow; ventral edge weakly pronounced. Quadrate plate with the dorsal region as broad as ventral region; dorsal margin convex; posterior margin complete. Oblong plate with posterior apodeme long. Triangular plate longer than broad. Gonostylus with body virtually fused to the oblong plate, with a single sclerotized anterior segment. Anal plate small and subtriangular. Lancet short, with functional valves; dorsal and ventral margins converging towards the apex. Sting sclerotized, with acute apex; body of bulb slender in lateral view. Furcula with dorsal arm fused to the base of the sting bulb.

Gyne. Ergatoid. Virtually identical to the conspecific worker except for the presence of the ocelli and wing buds, and the absence of a promesonotal suture.

Male. Body dark brown. Dorsum of head densely punctate; body predominantly smooth and weakly shiny. Short, subdecumbent, whitish hairs sparsely covering the body; appendages with fine apressed pubescence.

Head rounded. Mandibles falcate and relatively well developed, with a single tooth at apex. Palpal formula 1,2. Frontal lobes obsolete exposing the basilar condyle of antennae. Antennae 12-segmented; scape very short, pedicel enlarged. Ocelli present.

Pronotum reduced; scutum large and rounded, parapsidial lines distinct; prescutellum narrow; propodeum unarmed, with short dorsal face and distinctly concave declivous face in dorsal view, convex in side view; propodeal spiracle small, propodeal lobes reduced. Legs more elongate than in the conspecific females. Wing venation reduced; longitudinal veins Sc+R, Rs, M, Cu, and A present; cells C, R and SR closed. Hind wing with R cell only; four sub-median hamuli.

Petiole pedunculate, ventral processes absent. Postpetiole broader than long in dorsal view, attached to gaster by almost its full width. Gaster elongate, with rounded gastral shoulder.

Larvae. Profile pheidoloid, although the head does not protrude ventrally as much as in Pheidole larvae. Head subcircular; irregular, very reduced mandibles, apices do not meet, edentate; prothorax and abdomen relatively short, no protuberances. Body pilosity sparse and formed by smooth unbranched and short anchortipped hairs.

Etymology. The generic epithet refers to the keels under the female postpetiole; from Greek tropidos (τροπιδοσ) = keel, which, by virtue of being double ( Fig. 4 C), clearly differentiate these ants from all others, as far as we know.

Figures

FIGURE 1. SEM images of Tropidomyrmex elianae gen. & sp. n. paratype gyne. A, head in full face view; B, mesosoma in lateral view; C, mesosoma in dorsal view.

FIGURE 2. Auto-Montage images of Tropidomyrmex elianae gen. & sp. n. paratype gyne. A, head in full face view; B, lateral view; C, dorsal view. Images by April Nobile, specimen CASENT 0173620.

FIGURE 3. SEM images of Tropidomyrmex elianae gen. & sp. n. paratype gyne. A, detail of clypeal area in frontal view; B, detail of mouthparts in ventral view.

FIGURE 4. SEM images of Tropidomyrmex elianae gen. & sp. n. paratype gyne. A, detail of eye in lateral view; B, pretarsal claws of left hind leg; C, detail of subpostpetiolar process in ventral view (P: petiole, PP: postpetiole, G: gaster); D, detail of the declivous face of propodeum in dorsal view.

FIGURE 5. Line drawings of Tropidomyrmex elianae gen. & sp. n. sting apparatus (paratype worker). A, sting and furcula in dorsal view; B, sting and furcula in profile; C, oblong plate; D, anal plate; E, gonostylus; F, spiracular plate; G, triangular plate; H, quadrate plate.

FIGURE 6. SEM images of Tropidomyrmex elianae gen. & sp. n. paratype male (wings excluded). A, head in full face view; B, lateral view; C, mesosoma in dorsal view ..

FIGURE 7. SEM images of Tropidomyrmex elianae gen. & sp. n. paratype male. A, detail of mouthparts in frontal view; B, line drawings of (1) fore and (2) hind wings.

FIGURE 8. SEM images of Tropidomyrmex elianae gen. & sp. n. larvae. A, head in full face view (AB: antennal buds, MP: maxillary palps, LP: labial palps); B, detail of mouth area (MD: mandibles); C, body in profile; D, detail of ventral anchor-like hairs; E, detail of anal area in posterior view.

FIGURE 9. Line drawings of Tropidomyrmex elianae gen. & sp. n. worker from Tocantins. A, head in full face view; B, habitus.

FIGURE 10. Tropidomyrmex elianae gen. & sp. n. worker from Tocantins. A, head in full face view; B, mesosoma in lateral view; C, dorsal view.