Stenamma ignotum

Stenamma ignotum is found in a diversity of wet forest habitats (e.g. cloud forest, mesophyll forest, wet oak forest) from 500 m to 2070 m elevation, but is most common above 1,000 m. Most collections are from sifted leaf litter taken from the forest floor, but it is also known from cookie baits and by general searching. A couple of nests have been found: one underneath a rock, and the other under epiphytes on the ground, both in montane wet forest. A single stray worker has been collected from a mud bank.

Identification
Branstetter (2013) - Integument mostly dark brown to brown; small-sized species (see HL, ML, PrW below); basal margin of mandible straight, never with a basal notch or depression; anterior clypeal margin with a shallow median emargination (best viewed from an anterodorsal angle); face completely sculptured, mostly rugoreticulate; mesosoma mostly sculptured, dorsum of promesonotum with dense longitudinal rugae; eye of moderate size (EL 0.10–0.12, REL 18–21), oval-shaped, with 5–7 ommatidia at greatest diameter; gastral pilosity relatively long, sparse, and mostly su- berect, sometimes with a few underlying decumbent setae; petiole in profile appearing somewhat elongate; petiolar node reaching a distinct apex, which points vertically; propodeal spines tuberculate to short (PSL 0.07–0.12, PSI 1.2–2.1); frontal lobes of moderate width (FLD 0.14–0.16, FLI 24–27), not greatly obscuring torular lobes in full-face view. Similar species: Stenamma crypticum, Stenamma nonotch, Stenamma picopicucha.

Separable from similar species by having the basal margin of the mandible straight and the anterior clypeal margin with a distinct median emargination. Some specimens of S. nonotch have a nearly imperceptible notch in the anterior clypeal margin, but this is always very insignificant compared to the emargination present in S. ignotum. Sculpture on the pronotal dorsum can be compared to confirm species status, with S. ignotum always having distinct longitudinal carinulae and S. nonotch having rugoreticulae or very irregular rugae. Regarding S. crypticum and S. picopicucha, the latter species is intermediate between S. crypticum and S. ignotum and it is unclear to which it is most closely related.

There is some variation in size and sculpture among populations of S. ignotum, but the differences are minute. The only exception is a distinct variant (CASENT0604307) known from a single specimen from Guatemala (7.3km E Purulhá). This specimen has very long propodeal spines, and the dorsum of the petiolar node in profile reaches a rather sharp apex, which points distinctly posteriad.

Distribution
Southern Mexico to Honduras. No records from Belize.

Distribution based on Regional Taxon Lists
Neotropical Region: Guatemala, Mexico.

Male
Males have been collected but have not been described.

Nomenclature

 *  ignotum. Stenamma ignotum Branstetter, 2013: 133, figs. 96-99 (w.q.m.) COSTA RICA.

Worker
(18 measured) HL 0.59–0.68 (0.64), HW 0.53–0.61 (0.55), FLD 0.14–0.16 (0.14), PCW 0.02–0.03 (0.02), SL 0.47–0.55 (0.50), EL 0.10–0.12 (0.10), ACL 0.45–0.52 (0.49), ML 074–0.86 (0.74), PrW 0.36–0.43 (0.37), PSL 0.07–0.12 (0.07), SDL 0.05–0.07 (0.05), PL 0.25–0.32 (0.27), PH 0.15–0.18 (0.15), PW 0.11–0.16 (0.12), PPL 0.14–0.18 (0.15), PPH 0.13–0.17 (0.13), PPW 0.15– 0.19 (0.15), MFL 0.52–0.62 (0.54), MTL 0.42–0.50 (0.45), CI 87–92 (87), SI 85–96 (89), REL 18–21 (18), FLI 24–27 (26), PSI 1.2–2.1 (1.6), MFI 96–104 (103), ACI1 66–70 (67), ACI2 92–100 (98).

Small-sized species; general body color mostly dark brown to brown, with appendages brown to orange-brown, becoming lighter toward extremities; setae golden brown; mandible with 5–6 teeth, consisting of 3 distinct apical teeth, a basal tooth, and 1–2 smaller inner teeth/denticles, which are often worn and indistinct; basal margin of mandible straight, without basal notch or depression; mandible mostly smooth and shiny, with scattered piligerous punctae, and some striations around base and along lateral surface; anterior clypeal margin with a shallow median emargination (best viewed from anterodorsal angle); median lobe of clypeus with a pair of faint longitudinal carinulae that diverge toward anterior margin, apex of lobe with a short transverse carinula, remainder of clypeus mostly smooth; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.02–0.03), sides subparallel to slightly hour-glass-shaped; frontal lobes of moderate width (FLD 0.14–0.16, FLI 24–27), not greatly obscuring torular lobes in full-face view; head roughly oval-shaped (CI 87–92), with posterior margin slightly depressed medially; eye of moderate size (EL 0.10–0.12, REL 18–21), oval-shaped, with 5–7 ommatidia at greatest diameter; face mostly rugoreticulate, with some longitudinal rugae along midline; scape of moderate length (SI 85–96), almost reaching posterior margin when laid back; scape surface smooth and shiny, with scattered piligerous punctae; flagellum with distinct 4-segmented antennal club; mesosoma almost completely sculptured except for a small patch of smooth cuticle on side of pronotum; dorsum of pronotum densely rugose (longitudinal orientation), transitioning to rugoreticulae on mesonotum; upper half of side of mesonotum rugose; mesopleuron mostly punctate, with some rugulae; side of propodeum rugulose-punctate; dorsum and declivity of propodeum with transverse carinulae; promesonotum in profile low-domed, slightly asymmetrical with apex shifted anterior of midpoint; metanotal groove of moderate width and depth; propodeal spines tuberculate to short (PSL 0.07–0.12, PSI 1.2–2.1); petiole appearing of moderate length to slightly elongate (PL/HW 0.47–0.54); petiolar node in profile of moderate height (PH/PL 0.55–0.66), and roughly symmetrical, dorsum pointing vertically to slightly posteriad, and usually reaching a well-defined apex; postpetiole in profile slightly asymmetrical, with anterior face longer and more sloping than pos- terior face, overal size similar to petiolar node (PPH/PH 0.85–0.98); anterior faces of petiolar and postpetiolar nodes mostly smooth and shiny, remaining surfaces faintly punctate; gaster smooth and shiny, with scattered piligerous punctae; most of body dorsum with short to long standing pilosity; setae on gastral dorsum relatively sparse, mostly long and suberect, with a few shorter decumbent setae underneath; setae on scape and legs decumbent to appressed, with some longer suberect setae on femoral venters and coxae.

Queen
(5 measured) HL 0.66–0.74 (0.66), HW 0.61–0.67 (0.61), FLD 0.15–0.18 (0.15), PCW 0.02–0.03 (0.03), SL 0.52–0.58 (0.52), EL 0.17–0.20 (0.17), ACL 0.49–0.55 (0.49), ML 0.94–1.09 (0.94), PrW 0.54–0.63 (0.54), PSL 0.13–0.17 (0.13), SDL 0.09–0.10 (0.10), PL 0.37–0.40 (0.37), PH 0.19–0.22 (0.19), PW 0.16–0.19 (0.16), PPL 0.16–0.22 (0.16), PPH 0.18–0.23 (0.18), PPW 0.20– 0.24 (0.20), MFL 0.59–0.70 (0.59), MTL 0.50–0.58 (0.50), CI 90–93 (92), SI 85–91 (85), REL 28–30 (28), FLI 25–27 (25), PSI 1.4–1.7 (1.4), MFI 95–103 (1.03), ACI1 64–68 (67), ACI2 94–96 (96).

Same as worker except for standard queen modifications and as follows: pronotum with transverse rugae/carinulae; mesoscutum densely longitudinally carinulae; scutellum rugose to rugoreticulate; propodeum with transverse carinulae that wrap around entire surface; mesopleuron mostly smooth; gastral pilosity denser, especially lower decumbent layer; wing as in photograph.

Type Material
Holotype worker. MÉXICO: Chiapas, 2km SE Custepec, 15.72102°N, 92.95013°W ±50m, 1520m, 17 May 2008, mesophyll forest, ex sifted leaf litter (LLAMA, collection Wa-A-02-1-09) USNM, specimen CASENT0603762. Paratypes: same data as holotype 1w, CASC, CASENT0623311, 1w, EAPZ, CASENT0623312; same data but 3km ESE Custepec, 15.71660°N, 92.93715°W ±50m, 1700m, 18 Jul 2007 (J. Longino, JTL6073) 1w, ECOSCE, CASENT0620158, 1w, FMNH, CASENT0620159, 1w, ICN, CASENT0620160, 1w, INBC, CASENT0620161, 1w, LACM, CASENT0620162], 1w, MCZ, CASENT0622764, 1q, 1w, USNM, CASENT0600182, CASENT0622765; 15.71508°N, 92.93822°W ±50m, 1700m, 17 May 2008 (LLAMA, Wa-A-02-2-45) 1w, MZSP, CASENT0623320, 1w, UCDC, CASENT0623321, 1w, UNAM, CASENT0623322, 1w, UVGC, CASENT0623324, 1w, JTLC, CASENT0623323, 2w, MGBPC, CASENT0623326, CASENT0623325.

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
 * Dattilo W. et al. 2019. MEXICO ANTS: incidence and abundance along the Nearctic-Neotropical interface. Ecology https://doi.org/10.1002/ecy.2944
 * Longino J. et al. ADMAC project. Accessed on March 24th 2017 at https://sites.google.com/site/admacsite/