Temnothorax acutispinosus

Known only from a few collections, T. acutispinosus is presumed to be an arboreal species.

Identification
Prebus (2021) – The lone member of the acutispinosus group of the Temnothorax salvini clade. Temnothorax acutispinosus can be separated from all other species in the salvini clade by the following character combination: dorsum of mesosoma very weakly sinuate in profile view; hind femora weakly incrassate (FI 258–319); propodeal spines acute and directed dorsally; petiolar node rounded dorsally; postpetiole moderately broad (PWI 159–175); integument dark brown; setae on head, mesosoma, waist segments and gaster erect, short, sparse and blunt (never long and tapering).

Similar species: Temnothorax achii, Temnothorax altinodus, Temnothorax ixili, Temnothorax subditivus, Temnothorax tuxtlanus, Temnothorax xincai, members of the augusti, goniops, and pulchellus groups, and species of the sallei clade. Temnothorax acutispinosus can be distinguished from similar appearing members of the sallei clade (e.g., Temnothorax manni, Temnothorax mexicanus, Temnothorax punctithorax) by the petiole, which lacks a transverse carina anterodorsally. In contrast to all of the above species (except T. altinodus), T. acutispinosus has acute, dorsally directed propodeal spines. Temnothorax acutispinosus can be distinguished from T. altinodus by the relatively compact mesosoma (WLI 131–136 vs. 148 in T. altinodus) and weakly incrassate hind femora, which are enlarged in T. altinodus.

Distribution
Prebus (2021) - Southern Mexico to Honduras, mid elevations of the Sierra Madre de Chiapas and Central American Nucleus.

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

Biology
Prebus (2021) - Temnothorax acutispinosus is known from a few collections in mid elevation mesic forest in Chiapas state in Mexico and Comayagua in Honduras. This species is apparently a canopy dweller, and probably nests arboreally: the types were collected from under epiphytes on a treefall or via canopy baiting. Temnothorax acutispinosus is closely related to the rugosus and annexus species groups from Mexico north of the Isthmus of Tehuantepec and the Southwestern United States, all of which are apparently arboreal.

Nomenclature

 * . Temnothorax acutispinosus Prebus, 2021: 85, fig. 93 (w.) MEXICO (Chiapas).

Worker
(n = 3): SL = 0.533–0.608 (0.567); FRS = 0.201–0.232 (0.217); CW = 0.689–0.770 (0.725); CWb = 0.636–0.725 (0.675); PoOC = 0.287–0.324 (0.302); CL = 0.721–0.816 (0.764); EL = 0.165–0.195 (0.179); EW = 0.122–0.124 (0.123); MD = 0.180–0.210 (0.198); WL = 0.867–0.964 (0.899); SPST = 0.188–0.233 (0.211); MPST = 0.272–0.338 (0.298); PEL = 0.325–0.337 (0.331); NOL = 0.183–0.204 (0.195); NOH = 0.137–0.139 (0.138); PEH = 0.238–0.263 (0.25); PPL = 0.200–0.231 (0.213); PW = 0.402–0.464 (0.431); SBPA = 0.157–0.180 (0.166); SPTI = 0.208–0.210 (0.209); PEW = 0.148–0.170 (0.158); PNW = 0.155–0.163 (0.158); PPW = 0.258–0.271 (0.263); HFL = 0.564–0.652 (0.599); HFWmax = 0.144–0.169 (0.158); HFWmin = 0.050–0.062 (0.055); CS = 0.997–1.133 (1.057); ES = 0.227–0.257 (0.240); SI = 84; OI = 23; CI = 88–89 (88); WLI = 131–136 (133); SBI = 24–25 (25); PSI = 22–27 (24); PWI = 159–175 (166); PLI = 146–163 (156); NI = 134–149 (141); PNWI = 96–105 (100); NLI = 56–61 (59); FI = 258–319 (288).

In full-face view, head subquadrate, longer than broad (CI 88–89). Mandibles densely, finely striate but shining and armed with five teeth: the apical-most well developed and acute, followed by a less developed preapical tooth and three equally developed smaller teeth. Anterior clypeal margin emarginated medially. Antennal scapes short: when fully retracted, failing to reach the posterior margin of the head capsule by about the maximum width of the scape (SI 84). Antennae 12-segmented; antennal club of composed of three segments, with the apical-most segment slightly longer than the preceding two in combination. Compound eyes moderately protruding past the lateral margins of the head capsule. Frontal carinae short, extending past the antennal toruli by about one and a half times the maximum width of the antennal scape. Lateral margin of head weakly convex, forming a continuous arc from the mandibular insertions to the posterior margin of the head. Posterior head margin flat but rounding evenly into the lateral margins.

In profile view, compound eyes ovular and moderately large (OI 23), with 11 ommatidia in longest row. Pronotal declivity distinct: dorsal margin of anterior face of pronotum marked by a weak carina; neck and anterior face of pronotum forming a ~120° angle. Mesosoma very weakly sinuate: dorsum of promesonotum forming an even convexity between the pronotal declivity and the metanotum, metanotum and propodeum slightly depressed below the level of the promesonotum; metanotum slightly convex in some specimens; propodeal dorsum flat. Promesonotal suture extending from the posterior margin of the procoxal insertion to the mesothoracic spiracle, which is moderately well developed. Metanotal groove visible as a disruption of the sculpture laterally from where it arises between the mid- and hind coxae, continuing dorsally as a weak impression between the posterior margin of the mesonotum and the anterior margin of the metanotum. Propodeal spiracle weakly developed, directed posterolaterally, and separated from the propodeal declivity by about five spiracle diameters. Propodeal spines moderately long, about as long as the propodeal declivity (PSI 22–27), tapering evenly from the base, directed dorsally, and acute. Propodeal declivity with a fine carina joining the base of the propodeal spines and the propodeal lobes; weakly concave, forming a ~120° angle with the base of the propodeal spines. Propodeal lobes rounded and weakly developed. Metapleural gland bulla moderately large, extending from the metacoxal insertion two thirds of the way to the propodeal spiracle. Petiole short (PLI 146–163), with weakly developed tubercles anterodorsally. Subpetiolar process in the form of a moderately large, blunt, triangular tooth; ventral margin of petiole weakly bulging posterior to it. Petiolar peduncle short: comprising about a quarter of the total petiolar length. Petiolar node robust, erect, and rounded: transition between peduncle and node marked by a rounded angle of ~120°, resulting in a weakly concave anterior node face; anterior face rounding evenly into the convex dorsal face; dorsal face rounding evenly into the posterior face, which forms a ~120° angle with the caudal cylinder. Postpetiole evenly rounded anteriorly, strongly bulging anterodorsally, flattened posterodorsally; concave ventrally, with an acute, anteriorly directed subpostpetiolar process.

In dorsal view, humeri moderately well developed and distinct: evenly rounded and wider than the rest of the mesosoma; mesothoracic spiracles very weakly protruding past the lateral margins of the mesosoma, visible as slight angles where the pronotum meets the mesonotum. Promesonotal groove represented by a weak sulcus. Metanotum delineated anteriorly and posteriorly by very faint impressions. Propodeal spines narrowly approximated basally and diverging apically, their apices separated from each other by about their length, the negative space between them “U” shaped. Petiolar peduncle with spiracles weakly protruding past the lateral margins, but not noticeably constricted anterior to them. Petiolar node evenly ovular; node slightly wider than the peduncle, and evenly grading into the caudal cylinder, which the same width as the node. Postpetiole narrow (PWI 159–175) and subquadrate. Anterior margin of the postpetiole weakly convex and meets the lateral margins at a rounded ~90° angle; lateral margins parallel to each other; posterior margin flat. Metafemur moderately to strongly incrassate (FI 258–319).

Sculpture: median clypeal carina present, extending posteriorly nearly to the frontal triangle, and flanked on either side by two equally strong carinae. Lateral clypeal lobes with additional, weaker carinae; ground sculpture areolate. Antennal scapes shining through weak areolate ground sculpture. Cephalic dorsum areolate, with the areolae arranged into longitudinal rows by fine costulae. Lateral surfaces of head areolate, with sculpture similar to the dorsum of the head between the compound eye and the posterior margin of the head; sculpture between the compound eye and the mandibular insertion areolate-rugose. Ventral surface of head smooth and shining, with weak costulae. Pronotal neck areolate. Anterior face of the pronotum areolate. Lateral surface of the mesosoma areolate, with weak costulae overlying the ground sculpture on all surfaces except between the propodeal spiracle and the base of the propodeal spines. Dorsal surface of mesosoma areolate, with overlying rugose sculpture on the pronotum. Femora shining, with traces of weak areolate sculpture. Petiole and postpetiole predominantly areolate, but the anterior face of the postpetiole smooth and shining. First gastral tergite and sternite smooth and shining, with weak spectral iridescence.

Setae: antennal scapes and funiculi with short, adpressed pilosity. Dorsum of the head, pronotum, waist segments, and gaster with moderately abundant, erect, blunt-tipped setae, the longest of which are about the width of the compound eye. The head bears ~28, mesosoma ~16, petiole 6, postpetiole ~14, and first gastral tergite ~44 setae. Short, sparse pubescence present over the entire body, but difficult to detect against the densely sculptured integument.

Color: predominantly dark brown, with antennae, apices of mandibles, and legs testaceous. Sting testaceous yellow. Gyne: Unknown.

Type Material
Holotype worker: MEXICO: Chiapas: Custepec, 15.72196_N 92.95037_W ± 50 m, 1,530 m, 19 May 2008, J. Longino #6285, mesophyll forest, under epiphytes in treefall (JTLC000007447).

Paratype workers: MEXICO: Chiapas: same data as holotype, 1 worker (JTLC000007448) 1 worker (JTLC000007449)  1 worker (JTLC000007450)  2 workers (CASENT0869149, CASENT0869156)  1 worker (CASENT0869150)  1 worker (CASENT0869151)  1 worker (CASENT0869152)  1 worker (CASENT0869153)  1 worker (CASENT0869154)  1 worker (CASENT0869155) [CASC]; same data as holotype, except: J. Longino #6286, mesophyll forest, under epiphytes in treefall (CASENT0869119) [UNAM].

Etymology
Morphological, from the Latin ‘acutus’ (= sharp) + ‘spinosus’ (= thorny), a reference to the sharp, dorsally directed propodeal spines.