Stenamma expolitico, Branstetter, Michael G., 2013

Branstetter, Michael G., 2013, Revision of the Middle American clade of the ant genus Stenamma Westwood (Hymenoptera, Formicidae, Myrmicinae), ZooKeys 295, pp. 1-277 : 82-84

Stenamma expolitico sp. n. Worker: Figure 82; Map: Figure 81

Type material.

Holotype worker. COSTA RICA, Alajuela Prov.: Rio Peñas Blancas, 10.3167°N, 84.7167°W, 800m, 23 May 1990, wet forest, ex sifted leaf litter (J. Longino, collection JTL2701-s) [INBio, specimen INBIOCRI001282473]. Paratypes: COSTA RICA, Heredia: 16km N Vol. Barba, 10.267°N, 84.083°W, 1020m, 9 Jul 1986 (J. Longino, JTL1340-s) [1w, USNM, CASENT0623094]; same data but 22km N Volcan Barba, 10.333°N, 84.067°W, 500m, 5 Mar 1985 (J. Longino, JTL1340-s) [1w, LACM, CASENT0623093]; 16km SSE La Virgen, 10.267°N, 84.083°W, 1100m, 14-17 Mar 2001 (ALAS, 11/WF/02/28) [1w, UCD, INB0003212462].

Worker diagnosis.

Integument mostly black to dark red-brown; medium-sized species (see HL, ML, PrW below); petiole and postpetiole almost completely smooth and shiny, with only a few faint vestigial punctae sometimes present; postpetiole in profile bulging, globular, appearing more voluminous than petiolar node; face with a fan of carinae/rugae extending from frontal lobes to approximately ¾ distance to posterior margin of head, remainder of head smooth and shiny; dorsum of promesonotum with distinctive transverse furrows that reticulate toward posterior margin; propodeal spines absent to tuberculate (PSL 0.13-0.14, PSI 1.0-1.1), dorsal and declivitous faces of propodeum in profile flat, forming a blunt 90° angle; eye relatively large (EL 0.13-0.15, REL 19), with 8 ommatidia at greatest diameter; anterior clypeal margin with median emargination; basal margin of mandible straight; gastral setae long, sparse, and uniformly suberect. Similar species: Stenamma alas , Stenamma expolitum .

Geographic range.

Costa Rica.

Worker description.

(3 measured) HL 0.77-0.86 (0.77), HW 0.71-0.81 (0.71), FLD 0.21-0.24 (0.22), PCW 0.07-0.08 (0.07), SL 0.62-0.69 (0.62), EL 0.13-0.15 (0.13), ACL 0.60-0.65 (0.60), ML 1.07-1.20 (1.07), PrW 0.54-0.61 (0.54), PSL 0.13-0.14 (0.13), SDL 0.12-0.13 (0.12), PL 0.40-0.42 (0.40), PH 0.23-0.25 (0.23), PW 0.16-0.17 (0.16), PPL 0.24-0.27 (0.27), PPH 0.21-0.22 (0.21), PPW 0.21-0.22 (0.21), MFL 0.75-0.87 (0.75), MTL 0.62-0.70 (0.62), CI 92-94 (92), SI 85-88 (88), REL 19 (19), FLI 29-31 (31), PSI 1.0-1.1 (1.1), MFI 70-73 (70), ACI1 63-64 (64), ACI2 95-98 (97).

Medium-sized species; general body color black to dark red-brown, with brown patches on gaster; appendages mostly brown, changing to yellow-brown at extremities; setae golden brown; mandible with 5-7 teeth, consisting of 4 distinct apical teeth, a distinct basal tooth, and 1-2 worn denticles in between; basal margin of mandible straight, without a basal notch or depression; mandible surface with scattered piligerous punctae and faint striae; anterior clypeal margin with a median emargination; median lobe of clypeus obliquely flattened, mostly smooth and shiny, with a short transverse carinula near anterior margin, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions somewhat wide (PCW 0.07-0.08), with sides subparallel; frontal lobes somewhat narrow (FLD 0.0.21-0.24, FLI 29-31), not obscuring torular lobes in full-face view, outer margin of frontal lobes nearly parallel, almost without a discernable lateral apex; head subrectangular to oval-shaped (CI 92-94), with posterior margin flat, not depressed medially; eye relatively large (EL 0.13-0.15 REL 19), oval-shaped, with 8 ommatidia at greatest diameter; face with a fan of coarse carinae or costae extending from the frontal lobes to no more than ¾ distance to posterior margin of head; gena with short rugae and rugoreticulae; remainder of head mostly smooth and shiny; scape of moderate length (SI 85-88), not quite reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, with scattered piligerous punctae; flagellum with distinct 4-segmented antennal club; mesosoma densely sculptured, except for a patch of smooth, shiny cuticle on side of pronotum and katepisternum; dorsum of promesonotum with distinctive transverse furrows, which merge together posteriad and appear reticulate; sculpture on propodeum costate to rugose, with orientation transverse on dorsum, and longitudinal on side; mesopleuron rugose; propodeal declivity with faint transverse carinulae; promesonotum in profile low-domed and roughly symmetrical; metanotal grove somewhat indistinct and wide; propodeal spines absent to tuberculate (PSL 0.13-0.14, PSI 1.0-1.1), appearing in profile as a blunt 90° angle that separates dorsal and declivitous faces of propodeum; petiole of moderate length (PL/HW 0.52-0.56); petiolar node in profile robust and somewhat bulging (PH/PL 0.56-0.59), asymmetrical, with a longer more sloping anterior face and a short almost vertical posterior face; node dorsum flat to gently rounded and pointing posteriad; postpetiole in profile large, bulging, appearing slightly more voluminous than petiolar node, outline asymmetrical, with the anterior face longer and more gently sloping, and the posterior face short and vertical, dorsum of node broadly rounded; petiole and postpetiole mostly smooth and shining; gaster mostly smooth and shiny, with scattered piligerous punctae, and very short furrows around anterior constriction; most of body dorsum with long standing pilosity; scape setae suberect to subdecumbent; gastral setae long, somewhat sparse, and uniformly suberect; setae on legs suberect to subdecumbent, with longer suberect setae on coxae and femoral venters.

Queen.

Unknown.

Male.

Unknown.

Biology.

Stenamma expolitico is known from only four specimens, collected from sifted leaf litter in wet forest between 500-1100 m elevation.

Comments.

Stenamma expolitico belongs to the expolitum species group, which also includes Stenamma alas and Stenamma expolitum (a diagnosis for this group is given under Stenamma expolitum below). Stenamma expolitico can be separated from Stenamma alas and Stenamma expolitum by the presence of transverse furrows on the promesonotal dorsum, and by the shape of the propodeum in profile, which in Stenamma expolitico forms a blunt 90° angle where the dorsal and declivitous faces meet.

I am not completely convinced that Stenamma expolitico is a good species because it is known from only a few workers and is somewhat intermediate in morphology between Stenamma expolitum and Stenamma tico . It could be a hybrid form, or a rare variant of Stenamma expolitum or Stenamma alas . I choose to recognize it as separate species here, because, although rare, it does occur at several sites in sympatry with the other expolitum group species, and it is easily identifiable. Furthermore, many nests of Stenamma alas and Stenamma expolitum have been excavated, and workers with Stenamma expolitico -like morphology have never been found. More material of Stenamma expolitico , especially from nest series, is needed to test this hypothesis and confirm its status as a real biological species.

Material examined.

See type material.