Temnothorax acuminatus

Temnothorax acuminatus has been collected from several high elevation mesophyll forest localities in Chiapas state, Mexico. The type series was collected in the same treefall as the holotype of Temnothorax acutispinosus, under epiphytes and in bark crevices. Additional workers have been collected from Winkler leaf litter extraction and terrestrial baiting; it remains unclear whether this species is strictly arboreal. (Prebus 2021)

Identification
Prebus (2021) – A member of the acuminatus group of the Temnothorax salvini clade, T. acuminatus is most closely related to the only other member of its species group, Temnothorax tuxtlanus.

Temnothorax acuminatus can be separated from other salvini clade species by the following character combination: dorsum of mesosoma very weakly sinuate in profile view; dorsum of propodeum without erect setae; petiole with a weak transverse carina anterodorsally; petiolar peduncle short, comprising about a quarter of the total petiole length; petiolar node cuneiform; postpetiole relatively narrow (PWI < 170); setae on head, mesosoma, waist segments and gaster erect, short, sparse and blunt (never long and tapering); integument dark brown, with mandibles, pronotal neck, tibiae, tarsi, and sting testaceous brown.

Similar species: Temnothorax achii, Temnothorax acutispinosus, Temnothorax altinodus, Temnothorax ixili, Temnothorax subditivus, Temnothorax tuxtlanus, Temnothorax xincai, members of the augusti, goniops, and pulchellus groups, and species of the sallei clade. T. acuminatus may be separated from T. acutispinosus by the cuneiform petiolar node (rounded dorsally in T. acutispinosus), smaller subpetiolar tooth, and more posteriorly directed propodeal spines. Temnothorax acuminatus can be distinguished from similar appearing members of the sallei clade (e.g. Temnothorax manni, Temnothorax mexicanus, Temnothorax punctithorax) by the sculpture of the head: in similar looking sallei clade species, the head is mostly smooth and shining, with concentric rugulae surrounding the antennal insertions; additionally, the medial lobe of the clypeus is typically smooth, with three distinct longitudinal carina, whereas it is densely costulate-rugulose in T. acuminatus. In contrast to all of the remaining species above, T. acuminatus has a cuneiform petiolar node, a feature not found in other members of the salvini clade, except for Temnothorax rugosus. Temnothorax acuminatus is easily separated from T. rugosus by the smaller size, lack of medial notch in the anterior margin of the clypeus, lack of setae on the propodeal dorsum, and hind femora that are not incrassate.

Distribution
Mid-to-high elevations of the Sierra Madre de Chiapas mountains in southern Mexico.

Distribution based on Regional Taxon Lists
Neotropical Region: Mexico.

Nomenclature

 * . Temnothorax acuminatus Prebus, 2021: 75, figs. 90A, 91 (w.dq.) MEXICO (Chiapas).

Worker
(n = 5): SL = 0.450-0.509 (0.475); FRS = 0.175-0.219 (0.198); CW = 0.575-0.641 (0.611); CWb = 0.542-0.614 (0.575); PoOC = 0.282-0.316 (0.292); CL = 0.645-0.713 (0.666); EL = 0.143-0.164 (0.151); EW = 0.093-0.112 (0.102); MD = 0.132-0.153 (0.141); WL = 0.752-0.837 (0.785); SPST = 0.178-0.195 (0.189); MPST = 0.244-0.286 (0.261); PEL = 0.255-0.278 (0.269); NOL = 0.141-0.159 (0.151); NOH = 0.114-0.128 (0.119); PEH = 0.216-0.240 (0.227); PPL = 0.172-0.211 (0.191); PW = 0.363-0.418 (0.382); SBPA = 0.156-0.184 (0.168); SPTI = 0.187-0.239 (0.207); PEW = 0.147-0.166 (0.154); PNW = 0.112-0.115 (0.114); PPW = 0.227-0.243 (0.235); HFL = 0.487-0.539 (0.510); HFWmax = 0.118-0.131 (0.125); HFWmin = 0.044-0.048 (0.047); CS = 0.865-0.971 (0.908); ES = 0.192-0.218 (0.202); SI = 80-85 (83); OI = 22; CI = 84-88 (86); WLI = 132-139 (137); SBI = 27-30 (29); PSI = 22-26 (24); PWI = 144-164 (152); PLI = 131-158 (142); NI = 112-139 (127); PNWI = 68-78 (74); NLI = 52-61 (56); FI = 265-273 (269).

In full-face view, head subquadrate, longer than broad (CI 84-88). Mandibles weakly, 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 weakly convex. 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 80-85). Antennae 12-segmented; antennal club of composed of three segments, with the apical-most segment slightly longer than the preceding two in combination. Frontal carinae short, extending past the antennal toruli by about one and a half times the maximum width of the antennal scape. Compound eyes weakly protruding past the lateral margins of the head capsule. Lateral margin of head weakly convex, forming a continuous arc from the mandibular insertions to the posterior margin of the head. Posterior head margin weakly concave medially, rounding evenly into the lateral margins.

In profile view, compound eyes elongate-ovular and small (OI 22), with 10 ommatidia in longest row. Pronotal declivity indistinct, neck and anterior face of pronotum forming a ~120° angle. Mesosoma weakly sinuate: evenly convex from where it joins the pronotal neck to the metanotal groove; propodeum slightly depressed below the level of the promesonotum, and weakly convex. Promesonotal suture extending from the posterior margin of the procoxal insertion to the mesothoracic spiracle, which is moderately well developed, then continuing dorsally as a weak sulcus. Metanotal groove visible as a disruption of the sculpture laterally from where it arises between the mid- and hind coxae to the poorly developed metathoracic spiracle, which is nearly indistinguishable against the ground sculpture, then continuing dorsally as a weak impression. Propodeal spiracle weakly developed, directed posterolaterally, and separated from the propodeal declivity by about four spiracle diameters. Propodeal spines short (PSI 22-26), about two thirds the length of the propodeal declivity, tapering evenly from the base, straight, and acute. Propodeal declivity with a weak carinae joining base of propodeal spine and propodeal lobe; weakly concave, forming a rounded ~120° angle with the base of the propodeal spines. Propodeal lobes rounded and weakly developed, but dorsal margin weakly angulate. Metapleural gland bulla small, extending from the metacoxal insertion halfway to the propodeal spiracle. Petiole short (PLI 131-158), with tubercles anterodorsally. Subpetiolar process in the form of a small, blunt, triangular tooth which grades evenly into the ventral margin of the petiole posteriorly; ventral margin of petiole weakly bulging posterior to it. Petiolar peduncle short: comprising about a quarter of the total petiole length. Petiolar node erect and cuneiform: peduncle grading evenly into the anterior node face; anterior face forming a ~70° angle with the evenly rounded posterior face; posterior face forms a ~120° angle with the caudal cylinder. Postpetiole weakly rounded anteriorly, anterior face rounds evenly into the weakly rounded dorsal face; weakly lobed ventrally.

In dorsal view, humeri developed and distinct: evenly rounded and wider than the rest of the mesosoma; mesothoracic spiracles weakly protruding past the lateral margins of the mesosoma, visible as slight angles where the pronotum meets the mesonotum. Promesonotal groove visible as a weak sulcus and disruption in the ground sculpture. Metanotal groove visible as a weak impression. Propodeal spines broadly approximated basally and weakly diverging apically, their apices separated from each other by about twice 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, when viewed at a posterodorsal aspect, tapering evenly from the base, with the dorsal margin evenly and strongly convex; apex of node narrower than the peduncle and caudal cylinder. Postpetiole narrow (PWI 144-164) and subquadrate. Anterior margin of the postpetiole flat and evenly rounds into the lateral margins through a ~90° angle; lateral margins weakly converge to the rounded posterior corners; posterior margin broadly concave. Metafemur moderately incrassate (FI 265-273).

Sculpture: median clypeal carina present, extending posteriorly nearly to the frontal triangle, and flanked on either side by multiple weaker carinae; clypeus appears costulaterugulose. Lateral clypeal lobes with additional, weaker carinae; ground sculpture weakly areolate. Antennal scapes weakly areolate. Cephalic dorsum predominantly areolaterugulose, with the areolae arranged into longitudinal rows by fine costulae; very fine concentric rugulae surrounding the antennal insertions. Lateral surfaces of head sculptured similarly to the dorsum, but with areolae arranged into concentric whorls by fine costulae above the compound eyes; fine rugulose sculpture overlying the areolate sculpture between the compound eye and mandibular insertion. Ventral surface of head smooth and shining. Pronotal neck and anterior face of the pronotum shining through weak, transversely arranged areolae. Lateral surface of the pronotum shining medially, with weak costulae and areolae around the margins. Meso- and metapleurae areolate, with fine costulae overlying the ground sculpture. Smooth and shining between the propodeal spiracle and the propodeal spines. Dorsal surface of mesosoma uniformly areolate, with fine strigulae on the anterior margin of the pronotum. Femora shining, with weak areolate sculpture on the distal third. Petiole predominantly weakly areolate; anterior face of petiolar node smooth and shining. Postpetiole predominantly weakly areolate; anterior face smooth and shining. First gastral tergite and sternite smooth and shining, without spectral iridescence.

Setae: antennal scapes and funiculi with short, decumbent pilosity. Dorsum of the head, pronotum, waist segments, and gaster with moderately abundant, erect, blunt-tipped setae, the longest of which are about half the width of the compound eye. The head bears ~32, mesosoma ~16, petiole 4, postpetiole ~8, and first gastral tergite ~56 setae. Short, sparse pubescence present over the entire body, but difficult to detect against the densely sculptured integument.

Color: predominantly dark brown, with mandibles, pronotal neck, tibiae, tarsi, and sting testaceous brown.

Queen
(n = 3): SL = 0.495-0.513 (0.506); FRS = 0.22-0.231 (0.226); CW = 0.72-0.739 (0.727); CWb = 0.668-0.719 (0.691); PoOC = 0.295-0.304 (0.3); CL = 0.727-0.75 (0.739); EL = 0.212-0.22 (0.217); EW = 0.157-0.173 (0.164); MD = 0.139-0.159 (0.146); WL = 1.171-1.205 (1.193); SPST = 0.211-0.272 (0.247); MPST = 0.278-0.333 (0.307); PEL = 0.312-0.365 (0.343); NOL = 0.17-0.217 (0.197); NOH = 0.131-0.146 (0.139); PEH = 0.273-0.293 (0.28); PPL = 0.215-0.242 (0.225); APT = 1-1 (1); PW = 0.651-0.699 (0.677); SBPA = 0.305-0.325 (0.312); SPTI = 0.305-0.319 (0.311); PEW = 0.189-0.212 (0.204); PNW = 0.126-0.146 (0.138); PPW = 0.301-0.33 (0.314); HFL = 0.59-0.614 (0.603); HFWmax = 0.128-0.152 (0.138); HFWmin = 0.053-0.065 (0.059); CS = 1.032-1.094 (1.061); ES = 0.299-0.3 (0.299); SI = 71-74 (73); OI = 27-29 (28); CI = 92-96 (93); WLI = 167-176 (173); SBI = 43-47 (45); PSI = 18-23 (21); PWI = 147-159 (154); PLI = 145-168 (153); NI = 122-166 (143); PNWI = 59-75 (68); NLI = 54-62 (57); FI = 205-258 (235).

In full-face view, head subquadrate, slightly longer than broad (CI 92-96). Mandibles weakly striate but shining and armed with five teeth: the apical-most well developed, followed by a less developed preapical tooth and three equally developed smaller teeth. Anterior clypeal margin evenly convex medially. Frontal carinae moderately long, extending past the antennal toruli by about two times the maximum width of the antennal scape. Antennal scapes short: when fully retracted, failing to reach the posterior margin of the head capsule by about two times the maximum width of the scape (SI 71-74). Antennae 12-segmented; antennal club composed of three segments, with the apical-most segment slightly longer than the preceding two in combination. Compound eyes weakly protruding past the lateral margins of the head capsule. Lateral margins of head evenly convex behind the compound eyes, then parallel to each other from the mandibular insertions to below the compound eyes. Posterior head margin flat, rounding evenly into the lateral margins.

In profile view, compound eyes ovular and large (OI 27-29), with 17 ommatidia in longest row. Mesoscutum rounded evenly anteriorly, covering the dorsal surface of the pronotum, and flat dorsally. Mesoscutellum on the same plane as the mesoscutum; rounded posteriorly. Posterior margin of metanotum extending past the posterior margin of the mesoscutum. Propodeal spiracle moderately well developed, directed posterolaterally, and separated from the propodeal declivity by about four spiracle diameters. Propodeal spines thin and short (PSI 18-23), about a third as long as the propodeal declivity, tapering evenly from the base, straight, and blunt. Propodeal declivity with a carina joining base of propodeal spine and propodeal lobe; straight and flat, forming a rounded ~120° angle with the base of the propodeal spines. Propodeal lobes rounded and very weakly developed, but dorsal margin slightly angulate. Metapleural gland bulla small, extending from the metacoxal insertion halfway to the propodeal spiracle. Petiole moderately long (PLI 145-168), with flanges anterodorsally. Subpetiolar process in the form of a small, blunt, triangular tooth, which grades evenly into the ventral margin of the petiole posteriorly. Petiolar peduncle short: comprising about a third of the total petiole length. Petiolar node erect and cuneiform: peduncle transitioning evenly into the anterior node face; anterior face forming a blunt ~80° angle with the posterior face; posterior face forms a ~110° angle with the caudal cylinder. Postpetiole flat anteriorly, bulging slightly anterodorsally before it transitions into the flattened posterodorsal face; ventral surface weakly lobed.

In dorsal view, mesoscutum covering pronotum anteriorly, but humeri visible laterally as rounded sclerites. Propodeal spines parallel to each other, their apices separated from each other by about two and a half times their length. Petiolar peduncle with spiracles protruding past the lateral margins. Petiolar node, when viewed at a posterodorsal aspect, tapering dorsally; dorsal margin evenly convex. Apex of petiolar node about half as wide as the base; narrower than the peduncle caudal cylinder. Postpetiole narrow (PWI 147-159) and subquadrate. Anterior margin of postpetiole flat, with corners marked by rounded ~90° angles as it transitions to the lateral margins, which converge slightly to the rounded posterior corners; posterior margin flat. Metafemur weakly incrassate (FI 205-258).

Sculpture: median clypeal carina present, extending from the anterior margin nearly to frontal triangle, and flanked by weaker, indistinct carinae; clypeus appears costulaterugulose. Lateral clypeal lobes with additional weaker carinae; ground sculpture weakly areolate. Antennal scapes weakly areolate. Cephalic dorsum areolate-rugulose, with fine costulae arranging the areolae into columns. Fine concentric costulae surrounding the antennal insertions. Lateral surfaces of head sculptured similarly to the dorsum, but with areolae arranged into concentric whorls by fine costulae above the compound eyes; areolate-rugulose sculpture between the compound eye and mandibular insertion. Ventral surface of head shining, with weak costulae. Pronotal neck finely strigulate. Anterior face of pronotum smooth and shining. Lateral face of pronotum, katepisternum, and anepisternum weakly areolate, with weak costulae. Metapleural gland bulla with costate sculpture overlying it. Lateral face of propodeum areolate-strigulate. Propodeal declivity weakly areolate. Mesoscutum and mesoscutellum with costulae over weak areolate ground sculpture. Dorsum of propodeum areolate with concentric costulae overlying the ground sculpture. Femora smooth and shining, with traces of weak areolate sculpture. Petiole predominantly areolate-rugulose; anterior face of petiolar node smooth and shining. Postpetiole predominantly areolate-rugulose; anterior face smooth and shining. First gastral tergite and sternite smooth and shining, without spectral iridescence.

Setae: antennal scapes and funiculi with short, decumbent pilosity. Dorsum of the head, pronotum, waist segments, and gaster with moderately abundant, flexuous, tapering setae, the longest of which are about half the width of the compound eye. Short, sparse pubescence present over the entire body, but difficult to detect against the densely sculptured integument.

Color: predominantly dark brown, with mandibles, pronotal neck, tibiae, tarsi, and sting testaceous brown.

Type Material
Holotype worker: MEXICO: Chiapas: Custepec, ± 50 m, 1,530 m, 19 May 2008, J. Longino #6281, mesophyll forest, ex bark crevice in treefall (JTLC000007439).

Paratype workers and gynes: same data as holotype, 1 dealate gyne (JTLC000007440) [CASC]; same data as holotype, except: J. Longino #6286, under epiphytes in treefall, 1 dealate gyne (JTLC000007452) 1 worker (JTLC000007451) [MCZC] 1 worker (CASENT0869118) ; same data as holotype, except J. Longino #6278-s, mesophyll forest, foragers, 1 worker (JTLC000007468).

Etymology
Morphological, from the Latin ʻacuminatus' (= pointed, tapering), in reference to the cuneiform petiolar node.