Stenamma lagunum

Stenamma lagunum is known only from extractions of sifted leaf litter. It is a high-elevation species, occurring from 1730–1900 m and is found in mesic forest habitats, such as oak-pine forest, oak forest, and montane scrub.

Identification
Branstetter (2013) - Integument mottled, pale yellow-brown with patches of darker brown; small-sized species (see HL, ML, PrW below); head and mesosoma almost completely covered with light longitudinal rugulae; eye relatively small (EL 0.06–0.08, REL 10–13), subcircular, with 3–5 ommatidia at greatest diameter; basal margin of mandible slightly sinuous, without a basal notch or deep depression; anterior clypeal margin with a single median emargination; frontal lobes somewhat narrow, not completely obscuring torular lobes in full-face view (FLD 0.15-0.16, FLI 25-28); propodeal spines present, forming short broad triangles (PSL 0.11–0.12, PSI 1.4-1.6); gastral pilosity short and clearly bilayered, with a layer of suberect setae and a layer of decumbent setae. Similar species: Stenamma excisum, Stenamma californicum.

Stenamma lagunum is a very distinctive species that appears to be endemic to the mountains of southern Baja CA. It might be confused with its sister species S. excisum, but can be easily separated by its carinulate facial sculpture and more projecting median lobe of the clypeus. There is the chance that if S. lagunum occurs farther north in Baja CA, it might overlap with Holarctic clade Stenamma species, such as S. californicum. Holarctic clade species should be easy to separate out by their distinct clypeal carinae.

Distribution
Northwestern Mexico (Baja CA Sur). Known only from the Sierra La Laguna mountains.

Distribution based on Regional Taxon Lists
Neotropical Region: Mexico.

Castes
Males have yet to be collected.

Nomenclature

 *  lagunum. Stenamma lagunum Branstetter, 2013: 139, figs. 100-102 (w.q.) MEXICO.

Worker
(5 measured) HL 0.66–0.70 (0.68), HW 0.55–0.61 (0.58), FLD 0.15–0.16 (0.15), PCW 0.03–0.04 (0.04), SL 0.54–0.56 (0.56), EL 0.06–0.08 (0.06), ACL 0.54–0.58 (0.59), ML 0.79–0.85 (0.83), PrW 0.38–0.40 (0.39), PSL 0.11–0.12 (0.11), SDL 0.05–0.07 (0.06), PL 0.29–0.32 (0.30), PH 0.18–0.19 (0.19), PW 0.12–0.13 (0.13), PPL 0.16–0.17 (0.16), PPH 0.14–0.16 (0.15), PPW 0.15– 0.18 (0.17), MFL 0.59–0.60 (0.59), MTL 0.49–0.52 (0.52), CI 83–87 (86), SI 92–98 (95), REL 10–13 (10), FLI 25–28 (26), PSI 1.4–1.6 (1.4), MFI 94–101 (98), ACI1 65–67 (67), ACI2 97–103 (97).

Small-sized species; general body color a mottled pale yellow-brown with patches of darker brown, appendages similar; setae golden brown; mandible with 6 teeth, consisting of 2–3 distinct apical teeth, a basal tooth, and 2-3 middle teeth, which are usually worn and indistinct; basal margin of mandible straight to slightly sinuous, without a basal notch or deep depression; mandible mostly smooth and shiny, with scattered piligerous punctae; anterior clypeal margin with a median emargination, clypeus bordering emargination slightly projecting and attenuate, appearing translucent; median lobe of clypeus obliquely flattened, lacking longitudinal carinulae, apex near anterior clypeal margin with a short transverse carinula, remainder of clypeus smooth and shiny; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.03–0.04), sides subparallel; frontal lobes somewhat narrow (FLD 0.15–0.16, FLI 25–28), with underlying torular lobes clearly visible in full-face view; head appearing subrectangular to oval-shaped (CI 83–87), posterior margin flat to very slightly depressed medially; eye relatively small (EL 0.06–0.08, REL 10-13), subcircular, with 3–5 ommatidia at greatest diameter; face completely covered with longitudinal rugulae and piligerous punctae, rugulae sometimes merging, but never becoming truly reticulate, posterior margin of head near occipital foramen mostly smooth and shiny; scape of moderate length (SI 92–98), not quite reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, with scattered piligerous punctae and fine striations; flagellum with a somewhat distinct 4-segmented antennal club; mesosoma mostly with longitudinal carinulae and rugulae, some faint punctae also present on most surfaces (a few aberrant specimens with transverse carinulae on pronotum); propodeal dorsum and declivity with faint transverse carinulae; promesonotum in profile low-domed, roughly symmetrical; metanotal grove well demarcated, of moderate width and depth; propodeal spines present, forming short broad triangular projections (PSL 0.11–0.12, PSI 1.4–1.6); petiole in profile somewhat compact (PL/PW 51–55), node domed and pointing slightly posteriad, node dorsum flat to gently rounded; postpetiole somewhat dorsoventrally compressed, clearly smaller than petiolar node (PPH/PH 0.77–0.82); petiolar and postpetiolar nodes mostly smooth and shiny, remaining waist surfaces faintly punctate; gaster mostly smooth and shiny, with scattered piligerous punctae; most of body with short standing pilosity; setae on scape decumbent to appressed; gastral pilosity short, somewhat dense, and clearly bilayered, with a layer of suberect setae and a layer of decumbent setae (setae on head similar); setae on legs mostly decumbent to appressed, with some suberect setae on venter of profemur.

Queen
(1 measured) HL 0.71, HW 0.61, FLD 0.16, PCW 0.04, SL 0.57, EL 0.17, ACL 0.59, ML 0.97, PrW 0.50, PSL 0.15, SDL 0.15, PL 0.34, PH 0.21, PW 0.14, PPL 0.17, PPH 0.17, PPW 0.20, MFL 0.64, MTL 0.55, CI 86, SI 94, REL 29, FLI 26, PSI 1.7, MFI 96, ACI1 62, ACI2 103.

Same as worker except for standard queen modifications and as follows: body color a darker yellow-brown; pronotum with transverse carinulae on sides, smooth in middle; mesoscutum carinulate, with carinulae long and distinct; katepisternum mostly smooth; propodeum with transverse carinulae that wrap around surface; propodeal spines blunt, slightly longer.

Type Material
Holotype worker. MÉXICO: Baja California Sur, Sierra La Laguna, 23.54600°N, 110.00215°W ±10m, 1860m, 2 Oct 2010 (M. G. Branstetter, collection MGB1676) USNM, specimen CASENT0622371. Paratypes: same data as holotype but 23.56106°N, 110.01026°W ±10m, 1890m, 4 Oct 2010 (M. G. Branstetter, MGB1691) 1dq, 1w, USNM, CASENT0622384, CASENT0622386; 23.54580°N, 110.01047°W ±10m, 1730m, 3 Oct 2010 (M. G. Branstetter, MGB1684) 1w, CASC, CASENT0622377, 1w, EAPZ, CASENT0622378, 1w, ECOSCE, CASENT0622379, 1w, FMNH, CASENT0622380, 1w, ICN, CASENT0622376, 1w, INBC, CASENT0623327, 1w, JTLC, CASENT0623328, 1w, LACM, CASENT0623329, 1w, MGBPC, CASENT0623330, 1w, MCZ, CASENT0623331, 1w, MZSP, CASENT0623332, 1w, UCDC, CASENT0623333, 1w, UNAM, CASENT0623334, 1w, UVGC, CASENT0623335].

Etymology
The specific eptithet of this species refers to the type locality.

References based on Global Ant Biodiversity Informatics

 * Branstetter M.G. 2013. Revision of the Middle American clade of the ant genus Stenamma Westwood (Hymenoptera, Formicidae, Myrmicinae). ZooKeys 295: 1277