Octostruma excertirugis Longino

Longino, John T, 2013, A revision of the ant genus Octostruma Forel 1912 (Hymenoptera, Formicidae), Zootaxa 3699, pp. 1-61 : 29-32

Octostruma excertirugis Longino , sp. nov.

(Figs 1F, 3E, 5G, 12B, 14F, 23, 43)

Type material. Holotype worker: GUATEMALA, Izabal: 5 km NW Morales, 15.51465, -88.86440, ± 28 m, 280 m,

18 May 2009, 2° lowland rainforest, ex sifted leaf litter (LLAMA, Wm-B-04-1-09) [CAS, unique specimen identifier CASENT0629828]. Paratype workers, queen: same data [EAPZ, CASENT0629829; ECOSCE, CASENT0629830; CAS, CASENT0629831; JTLC, CASENT0629832]; same data except 15.51430, -88.86479, ± 50 m, 250 m, 17 May 2009 (LLAMA, Wa-B-04-2-36) [USNM, CASENT0610160; MCZC, CASENT0610161]; 15.51351, -88.86647, ± 26 m, 245 m (LLAMA, Wm-B-04-1-01) [UVGC, CASENT0611289; INBC, CASENT0611290; MZSP, CASENT0611291].

Geographic range. Mexico (Chiapas) to Costa Rica.

Diagnosis. Face lacking transverse arcuate carina; basal five teeth of mandible bluntly rounded (Fig. 3E); face sculpture longitudinally rugose; ground pilosity fully appressed; first gastral tergite punctate on anterior half, fading to nearly smooth and shining posteriorly.

Description. Worker. HW 0.57-0.66, HL 0.55-0.63, WL 0.64-0.77, CI 103-110 (n=15). Labrum as in Fig. 1F, wider than long, strap-like lateral portions converging from base to near apex, joined by thin translucent cuticle medially but leaving distinctly bilobed apex, with distinct median notch; mandible triangular, in profile view with mandible closed, in same plane as clypeus, apex of mandible not down-turned; mandible with 8 teeth (Fig. 3E), tooth 1 continuous with basal rim of dorsal surface, teeth 1-5 bluntly rounded, similar in shape, a minute denticle between 4 and 5, teeth 6-7 smaller, not as blunt, tooth 8 long and acute; masticatory margin evenly curved, with no development of downturned apical fork; dorsal surface of mandible punctate; ventral surface concave, twisting toward articulation, broad basally and narrowing abruptly to narrow apical half to third; scape flattened, with pronounced anterobasal lobe, dorsal surface somewhat roughened; clypeus with broad, shallow emargination anteriorly; clypeus and face irregularly longitudinally rugose; frontal carinae faint, nearly obsolete; antennal socket deep, dorsal rim of socket continuous with pronounced dorsal margin of antennal scrobe; antennal scrobe deep, pocket-like, strongly delimited dorsally, posteriorly, and ventrally with sharply defined thin cuticular rim; compound eye small, circular, composed of about 7 ommatidia; feeble carina extends from ventral margin of antennal socket across floor of scrobe to compound eye; at about midlength on ventral margin of scrobe a variably-developed short carina extends perpendicularly onto floor of scrobe; ventral half of scrobe floor anterior to this short carina shallowly foveolate, rest of scrobe floor smooth, matte; vertex margin anterior to occipital carina densely punctulate, matte (top of head, not visible in face view); occipital carina extends a short distance onto ventral surface of head, fading before reaching level of compound eye; undersurface of head rugulose.

Promesonotum and dorsal face of propodeum forming an even convexity in profile, promesonotal suture not impressed, promesonotum with broad, weak, longitudinal impression; metanotal groove not impressed; propodeum with distinct dorsal and posterior faces meeting at a broadly obtuse angle; propodeal spines well-developed , in the form of right-angled flat translucent perpendicular plates, extending ventrally as thin carinae; irregular rugulae extend between propodeal spines, faint to absent medially, weakly separating dorsal and posterior faces of propodeum; propodeal spiracle large, diameter similar to width of base of propodeal spine, located below propodeal spine and abutting posterior margin; all surfaces of mesosoma matte; dorsum of promesonotum irregularly rugose, dorsal face of propodeum faintly punctate, posterior face of propodeum smooth, lateral pronotum punctate; dorsolateral propodeum punctate, lower propodeum and mesopleuron confluent and smooth.

Petiole in profile with peduncle differentiated from node, node with differentiated anterior face; node subquadrate, with long sloping dorsal face and short vertical posterior face; anteroventral margin with pronounced, anteriorly-directed peg-like tooth; postpetiole low, broad, crescent-shaped in dorsal view; dorsum of petiolar node and postpetiole punctate; first gastral tergite and sternite anteriorly with dense, confluent puncta , on disc puncta are sparse with smooth shiny interspaces, on posterior margin puncta are more dense but smaller than anterior puncta and not confluent.

Anterior labral lobe with radiating tuft of soft, thick, translucent, capitate setae of unequal length projecting from apex (like Fig. 2); each larger mandibular tooth with fully appressed seta running length of tooth; anterior margin of scape with about 11 spatulate setae; clypeus and face with fine, sparse fully appressed ground pilosity; face typically with 10 erect spatulate setae arranged as in Fig. 5G; pronotum with one pair erect setae on humeri; mesonotum with a pair of erect spatulate setae; mesotibia with conspicuous spatulate ground pilosity, about 5 short spatulate setae of variable length at apex; petiole with 2 erect setae; postpetiole with 2 erect setae; first gastral tergite with 2 spatulate setae at posterior margin, 2-6 (usually 2) setae on disc, ground pilosity fully appressed, sparse (length of setae less than distance between them); first gastral sternite with abundant short clavate to spatulate setae on posterior half to two thirds of sternite.

Color red brown.

Queen. HW 0.58-0.64, HL 0.61-0.65, WL 0.81-0.90, CI 95-101 (n=5). Head shape as in Fig. 14F; labrum, mandible, scape, and head sculpture similar to worker; antennal scrobe floor entirely smooth and matte; face with about 8 erect setae distributed as in worker, plus 2-6 on central frons, anterior to lateral ocelli; ocelli distinct; compound eye large, multifaceted, about 12 ommatidia in longest row.

Mesosoma with queen-typical alar sclerites; pronotum shallowly rugulose anteriorly, with dense confluent puncta laterally; mesoscutum, axilla, and scutellum shallowly longitudinally rugulose; anepisternum and katepisternum separated by strong sulcus; anepisternum, katepisternum, and most of side of propodeum with dense confluent puncta , with smooth matte patch in center of lower side of propodeum; dorsal face of propodeum faintly punctate; posterior face of propodeum smooth and shining dorsally, faintly foveolate ventrally; propodeal spines similar to worker; first gastral tergite and sternite with relatively uniform puncta , interspaces subequal in width to puncta , smooth and shining; pronotum with 2-4 erect setae, mesoscutum with 2-6, axilla, scutellum, and metanotum lacking erect setae, petiolar node with 2, postpetiolar disc with 2, first gastral tergite with about 10. Other characters similar to worker.

Biology. Octostruma excertirugis is a moderately abundant lowland species from Mexico to Costa Rica. All records are from sea level to 800 m. It occurs in mature to highly disturbed rainforest and in seasonal moist forest. All collections are from Berlese and Winkler samples of sifted litter and rotten wood from the forest floor. In quantitative 1 m 2 litter plot samples, it can occur in up to 16% of samples and is as or more abundant in second growth forest than in mature forest. Dealate queens are occasionally found together with workers in litter samples.

Etymology. The name refers to the pronounced rugae on the face, that often project through the soil layer. It is a dative plural noun and thus invariant.