Temnothorax pilicornis

Temnothorax pilicornis is known only from the islands off the coast of Baja California, where it has been collected from pitfall traps. This species has large eyes and lightly colored integument, which are typical of crepuscular species in xerophytic habitats. (Prebus 2021)

Identification
Prebus (2021) – The lone member of the pilicornis species group of the Temnothorax salvini clade.

Temnothorax pilicornis can be separated from all other species in the salvini clade by the following character combination: compound eyes large (OI ≥ 27); propodeal spines shorter than the propodeal declivity (PSI 27-29) and directed posteriorly, forming a rounded ~90° angle with the declivity; hind femora moderately to strongly incrassate (FI 282-323); petiolar node erect and subquadrate, not overhanging the caudal cylinder in profile view; postpetiole moderately broad (PWI 207-223); base of first gastral tergite sculptured; antennal scapes with dense suberect pilosity; setae on head, mesosoma, waist segments and gaster erect, short, sparse and blunt; integument light yellow.

Similar species: Temnothorax anaphalantus, Temnothorax andrei, Temnothorax carinatus, Temnothorax cokendolpheri, Temnothorax goniops, Temnothorax nitens, Temnothorax pseudandrei, Temnothorax wardi, species of the annexus and silvestrii groups. At first glance, this species is very similar to T. andrei or T. carinatus, but the broad post-petiole and areolate-costulate dorsum of the head is an indication of its true affiliation with the salvini clade. Temnothorax pilicornis can be separated from T. andrei, T. anaphalantus, T. carinatus, T. cokendolpheri, T. nitens, T. pseudandrei and the annexus group by the very broad postpetiole (PWI >200). Temnothorax pilicornis can be further separated from the annexus group, as well as T. wardi by the entire and evenly convex anterior clypeal margin, which is emarginate in the latter two. The sculpture, petiole, and propodeal spines of T. carinatus, T. cokendolpheri, and T. wardi differ from T. pilicornis as well, with the former three having weak areolate-costulate sculpture on the head (generally with a medial strip of smooth sculpture), a less pedunculate petiole, and the spines reduced to weak angles. Temnothorax pilicornis can be separated from members of the silvestrii group by the placement of the compound eyes, which are separated from the mandibular insertions by about their total length in T. pilicornis, but by more than their total length in the silvestrii group; the posterior margin of the head is convex in the silvestrii group, but flat in T. pilicornis; the anterior clypeal margin is flat in the silvestrii group, but convex in T. pilicornis This species differs from T. goniops and Temnothorax terrigena by the subdecument pilosity on the antennal scapes, which is decumbent in T. goniops and T. terrigena.

Distribution
Low elevations of Baja California.

Distribution based on Regional Taxon Lists
Neotropical Region: Mexico.

Nomenclature

 * . Temnothorax pilicornis Prebus, 2021: 255, fig. 132 (w.) MEXICO (Baja California Sur).

Worker
(n = 5): SL = 0.423-0.490 (0.460); FRS = 0.156-0.188 (0.173); CW = 0.517-0.602 (0.561); CWb = 0.469-0.549 (0.508); PoOC = 0.222-0.245 (0.235); CL = 0.606-0.689 (0.644); EL = 0.149-0.170 (0.161); EW = 0.118-0.139 (0.125); MD = 0.111-0.157 (0.138); WL = 0.702-0.817 (0.755); SPST = 0.192-0.219 (0.206); MPST = 0.209-0.255 (0.233); PEL = 0.266-0.319 (0.291); NOL = 0.143-0.182 (0.164); NOH = 0.096-0.122 (0.105); PEH = 0.202-0.242 (0.224); PPL = 0.188-0.213 (0.199); PPH = 0.198-0.241 (0.212); PW = 0.344-0.396 (0.364); SBPA = 0.142-0.187 (0.162); SPTI = 0.192-0.245 (0.213); PEW = 0.144-0.183 (0.161); PNW = 0.144-0.183 (0.163); PPW = 0.314-0.39 (0.348); HFL = 0.451-0.542 (0.501); HFWmax = 0.126-0.142 (0.137); HFWmin = 0.042-0.049 (0.046); CS = 0.772-0.894 (0.830); ES = 0.209-0.237 (0.224); SI = 89-96 (91); OI = 26-28 (27); CI = 77-80 (79); WLI = 148-150 (149); SBI = 29-34 (32); PSI = 27-29 (27); PWI = 207-223 (216); PLI = 130-168 (147); NI = 140-175 (156); PNWI = 100-106 (101); NLI = 53-61 (56); FI = 282-323 (300).

In full-face view, head subquadrate, elongate (CI 77-80). 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 evenly convex 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 89-96). Antennae 12-segmented; antennal club of composed of three segments, with the apical-most segment longer than the preceding two in combination. Frontal carinae long, extending past the antennal toruli by about four times the maximum width of the antennal scape. Compound eyes moderately protruding past the lateral margins of the head capsule. Lateral margin of head very weakly convex, nearly flat. Posterior head margin flat but rounding evenly into the lateral margins.

In profile view, compound eyes ovular and large (OI 26-28), with 12 ommatidia in longest row. Pronotal declivity distinct, neck and anterior face of pronotum forming a ~110° angle; anterior face and dorsal face forming a rounded ~110° angle. Mesosoma very weakly convex from the pronotal declivity to the propodeal spines, nearly flat; propodeum very weakly depressed, so that the dorsal margin dips slightly anterior to the base of the propodeal spines. Promesonotal suture extending from the posterior margin of the procoxal insertion only to the mesothoracic spiracle, which is weakly developed. Metanotal groove visible as a disruption of the sculpture laterally from where it arises between the mid- and hind coxae to where it ends in the poorly developed metathoracic spiracle, which is nearly indistinguishable against the ground sculpture. Propodeal spiracle poorly developed, directed posterolaterally, and separated from the propodeal declivity by about four spiracle diameters. Propodeal spines moderately well developed and moderately long (PSI 27-29), about as long as the propodeal declivity, flared at the base, straight, directed posterodorsally, and blunt. Propodeal declivity flat, forming a rounded ~90° angle with the base of the propodeal spines. Propodeal lobes rounded and weakly developed. Metapleural gland bulla small, extending from the metacoxal insertion halfway to the propodeal spiracle. Petiole short (PLI 130-168), without tubercles anterodorsally. Subpetiolar process in the form of a moderately large, blunt tooth, with a posterior flange that extends along most of the ventral face of the petiole. Petiolar peduncle short: petiolar node covering most of the petiolar dorsum. Petiolar node robust: node transitioning evenly to the petiolar peduncle anteriorly, with a weakly concave anterior face; anterior face forming a ~100° angle with the dorsal face, which is weakly convex; dorsal face rounding evenly into the short posterior face, which forms a ~100° angle with the caudal cylinder. Postpetiole evenly rounded anteriorly, flattened dorsally, and lobed ventrally.

In dorsal view, transition between the dorsum and the anterior face of the pronotum marked by a distinct carina. Humeri developed and distinct: anterior face of the pronotum meeting the lateral face at a distinct ~90° angle; mesothoracic spiracles weakly protruding past the lateral margins of the mesosoma, visible as slight angles where the pronotum meets the mesonotum. Promesonotal suture indicated by a change in sculpture and slight change in color of the integument. Metanotal groove absent: mesonotum and propodeum completely fused and lateral margins converging evenly to the bases of the propodeal spines. Propodeal spines broadly 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 not protruding past the lateral margins. Petiolar node campaniform: rounded anteriorly and very weakly convex posterior, nearly flat; node slightly wider than the peduncle, and evenly grading into the caudal cylinder, which is wider than the node. Postpetiole moderately broad (PWI 207-223) and campaniform, articulating with the nearly the entire anterior margin of the gaster, but leaving angulate corners of the gaster exposed on each side. Anterior margin of the postpetiole broadly convex and evenly rounds into the lateral margins, which diverge slightly to the angulate posterior corners; posterior margin broadly concave. Metafemur moderately to strongly incrassate (FI 282-323).

Sculpture: median clypeal carina present but may be difficult to distinguish from the costulate ground sculpture; extending posteriorly to the level of the antennal toruli and flanked on either side by two equally strong carinae. Lateral clypeal lobes with additional, weaker carinae; ground sculpture densely areolate-costulate. Antennal scapes shining through weak areolate ground sculpture. Cephalic dorsum densely areolate-costulate. Lateral surfaces sculptured similarly to the dorsum, but with stronger rugulae between the compound eye and the mandibular insertion. Ventral surface of head smooth and shining through weak areolate sculpture. Mesosoma with areolate sculpture on the pronotal neck. Lateral surface mesosoma densely areolate. Propodeal declivity densely areolate. Dorsal surface of pronotum with costulae over dense areolate ground sculpture; remainder of the mesosoma densely areolate, with costulae on the lateral margins and strigulae directly anterior to the base of the propodeal spines. Femora shining through weak areolate sculpture. Petiole and postpetiole uniformly areolate; petiole with a weak carina that extends from the spiracle to the caudal cylinder. Gaster very weakly areolate on the basal quarter of the first gastral tergite; otherwise smooth and shining, without spectral iridescence.

Setae: antennal scapes and funiculi with short, subdecumbent pilosity. Dorsum of the head, pronotum, waist segments, and gaster with moderately abundant, erect, blunt-tipped setae, some of which are nearly clavate. The longest setae are about half the width of the compound eye. The head dorsum bears ~28, mesosoma ~16, petiole 6, postpetiole ~12, and first gastral tergite ~34 setae. Longer, tapering setae are present on the ventral surface of the head, propleuron, procoxae, and ventral surface of the gaster. Short, sparse pubescence present over the entire body, but is difficult to detect against the lightly colored integument and dense sculpture.

Color: predominantly light yellow; masticatory margin of the mandible dark brown.

Type Material
Holotype worker: MEXICO: Baja California Sur: Isla Carmen, S end,, 20 m, 18 July 1999, A.M. Boulton #245, pitfall trap (CASENT0756186, top specimen on pin).

Paratype worker: same pin as holotype, 1 worker (bottom specimen on pin) [CASC].

Etymology
Morphological, from the Latin ʻpilus' (= hair) + ʻcornis' (= horned), in reference to the dense suberect pilosity on the antennal scapes.

Determination Clarifications
Leptothorax sp. BCA-6. Johnson & Ward, 2002: 1023.