Stenamma leptospinum

Stenamma leptospinum is known only from Winkler and Berlese samples of sifted leaf litter taken from the forest floor. It has been collected from 1650–2000 m elevation in montane wet forest habitats, including cloud forest and montane oak forest.

Identification
Branstetter (2013) - Integument mostly dark brown to brown; medium-sized species (see HL, HW, ML below); lateral margin of hypostomal bridge with a projecting subquadrate to broadly-rounded lobe (usually visible behind mandible in profile); propodeal spines long and rather slender (PSL 00.17–0.22, PSI 1.9–2.2); anterior clypeal margin with a median emargination; basal margin of mandible straight, without a basal notch or depression; head and mesosoma densely carinulate; eye large (EL 0.13–0.15, REL 16–19), with 6–8 ommatidia at greatest diameter; petiolar node in profile subconical, with apex well-defined, almost sharp; postpetiolar node anteroposteriorly compressed; gastral pilosity with a layer of long suberect setae and a sparse layer of shorter decumbent setae; frontal lobes of moderate width (FLD 0.21–0.23, FLI 26–31), not completely obscuring torular lobes in full-face view.

This species could be confused with Stenamma longinoi, Stenamma manni, or Stenamma muralla, but it should be easy to distinguish by its dense carinulate sculpture and long, slender propodeal spines. It is worth noting that the lateral hypostomal lobe that groups S. leptospinum with the other similar species is sometimes reduced, usually becoming shorter and only broadly rounded. When the lobe is reduced it can be more difficult to see in profile view, but it should still be visible from a lateroventral view. I have not seen any specimens where it is completely reduced to a point, as in most other species of Stenamma.

Distribution
Southern Mexico. Known only from a few localities in the Sierra Juarez Mountains in Oaxaca Mexico.

Distribution based on Regional Taxon Lists
Neotropical Region: Mexico.

Castes
Known only from the worker caste.

Nomenclature

 *  leptospinum. Stenamma leptospinum Branstetter, 2013: 143, figs. 102, 103 (w.) MEXICO.

Worker
(10 measured) HL 0.80–0.93 (0.91), HW 0.70–0.87 (0.87), FLD 0.21–0.23 (0.23), PCW 0.04–0.08 (0.04), SL 0.69 –0.80 (0.75), EL 0.13–0.15 (0.15), ACL 0.62–0.68 (0.68), ML 1.02–1.18 (1.17), PrW 0.47–0.55 (0.55), PSL 0.17–0.22 (0.22), SDL 0.08–0.10 (0.10), PL 0.35–0.43 (0.42), PH 0.22–0.26 (0.26), PW 0.15–0.19 (0.19), PPL 0.19–0.25 (0.25), PPH 0.20–0.25 (0.25), PPW 0.19– 0.25 (0.24), MFL 0.79–0.92 (0.89), MTL 0.63–0.74 (0.73), CI 87–96 (96), SI 87–98 (87), REL 16–19 (18), FLI 26–31 (26), PSI 1.9–2.2 (2.2), MFI 88–97 (97), ACI1 63–66 (64), ACI2 85–92 (91).

Medium-sized species; general body color dark brown to brown, with append-ages brown to orange-brown; setae dark golden brown; mandible with 6 teeth, with two teeth nearest basal tooth smaller, often worn and indistinct; basal margin of mandible straight, without a basal notch or depression; mandible surface mostly smooth and shiny, with scattered piligerous punctae; anterior clypeal margin with a median emargination; median lobe of clypeus with a pair of faint longitudinal carinulae that diverge anteriorly, apex with a short transverse carinula, remainder of clypeus mostly smooth and shiny, with a few faint striae on median lobe; posterior extension of clypeus between antennal insertions of moderate to somewhat wide width (PCW 0.04–0.08); frontal lobes of moderate width (FLD 0.21–0.23, FLI 26–31), not completely obscuring torular lobes in full-face view; lateral margin of hypostomal bridge with a projecting subquadrate to broadly-rounded lobe that is usually visible behind mandible in profile, but some specimens with lobe reduced; head subcircular to oval-shaped (CI 87–96), posterior margin with a slight median depression; eye large (EL 0.13–0.15, REL 16–19), roughly oval-shaped, with 6–8 ommatidia at greatest diameter; face densely sculptured with a fan of longitudinal carinulae that extend outward from frontal lobes, lateral margins with shorter less densely spaced rugulae, interstices faintly punctate; scape of moderate length (SI 87–98), nearly reaching posterior margin of head when laid back; scape surface mostly smooth and shiny with scattered piligerous punctures; flagellum with a somewhat distinct 4-segmented antennal club; mesosoma densely sculptured; promesonotum mostly longitudinally carinulate, with some transverse carinulae wrapping around anterior declivity; mesopleuron and side of propodeum with irregular rugulae, rugoreticulae, and punctae; propodeal dorsum and part of declivity with transverse carinulae, remainder of declivity smooth and shining; promesonotum in profile low-domed and somewhat asymmetrical, with posterior slope longer and shallower than anterior slope; metanotal grove well demarcated and moderately deep, forming a rather smooth transition with promesonotum; anterior margin of propodeal dorsum in profile sometimes distinctly raised and separated from metanotal grove; propodeal spines long and rather slender (PSL 00.17–0.22, PSI 1.9–2.2), pointing anteroposteriorly and outward from body; petiole of moderate length (PL/HW 0.47–0.51), peduncle in profile somewhat slender; petiolar node in profile somewhat high (PH/PL 0.59–0.69), subconical and roughly symmetrical, with a well-defined apex that points vertically; postpetiolar node in profile usually somewhat anteroposteriorly compressed, with apex rounded and pointing vertically or slightly posteriad; anterior faces of petiolar and postpetiolar nodes smooth and shiny, posterior faces with punctae and a few rugulae, remaining surface of waist punctate; gaster mostly smooth and shiny, with scattered piligerous punctae and a few short striae around anterior constriction; most of body with rather long standing pilosity; scape with a uniform layer of subdecumbent to appressed setae; gaster with a layer of long suberect setae and a sparse layer of shorter decumbent setae; setae on legs mostly subdecumbent to appressed, with suberect setae on coxae and femoral venters.

Type Material
Holotype worker. MEXICO: Oaxaca, 22.4km SW Valle Nacional, 17.59112°N, 96.39138°W ±20m, 1990m, 13 Aug 2009, cloud forest, ex sifted leaf litter (M. G. Branstetter, collection MGB1391) USNM, specimen CASENT0605530. Paratypes: same data as holotype 1w, CASC, CASENT0605531, 1w, MGBPC, CASENT0605555, 1w, MCZ, CASENT0605532, 1w, UCDC, CASENT0605529, 1w, UNAM, CASENT0605533, 1w, USNM, CASENT0605554].

Etymology
The specific epithet leptospinum refers to the long (for Stenamma), slender propodeal spines of this species.

References based on Global Ant Biodiversity Informatics

 * Dattilo W. et al. 2019. MEXICO ANTS: incidence and abundance along the Nearctic-Neotropical interface. Ecology https://doi.org/10.1002/ecy.2944