Messor odrysarum Lapeva-Gjonova & Borowiec 2026, sp. nov.

Messor odrysarum Lapeva-Gjonova & Borowiec sp. nov. Figs 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 Material examined. Holotype: Bulgaria • 1 w. (pin), East Rhodopes, Kardzhali district, Sokolyane, 41°45.38'N, 25°25.92'E, alt. 468 m, 15 Sept. 2025, leg. A. Lapeva-Gjonova, BFUS Collection, Catalog Number: BFUS -I-AG 003233. Paratypes: BULGARIA • 7 w. (pin): the same locality as holotype, 25 Aug. 2022, leg. A. Lapeva-Gjonova (BFUS: from BFUS -I-AG 003201 to BFUS -I-AG 003207); • 14 w. (pin): the same locality as holotype, 03 June 2025, leg. A. Lapeva-Gjonova (BFUS: from BFUS -I-AG 003208 to BFUS -I-AG 003221); • 4 w. (pin): the same locality as holotype, 03 June 2025, leg. A. Lapeva-Gjonova (MNHW); • 1 g. (pin) (BFUS: BFUS -I-AG 003229), 3 m. (pin) (BFUS: from BFUS -I-AG 003230 to BFUS -I-AG 003232), 8 w. (pin) (BFUS: from BFUS -I-AG 003221 to BFUS -I-AG 003228): the same data as holotype, leg. A. Lapeva-Gjonova; • 1 g., 1 m., 3 w. (pin): the same data as holotype, leg. A. Lapeva-Gjonova (MNHW); • 4 w. (3 EtOH / 1 pin): Eastern Rhodopes, Kardzhali district, Oreshari vill., 41°36.59'N, 25°43.04'E, alt. 111 m, 22 Apr. 2014, leg. A. Lapeva-Gjonova (MNHW); • 1 w. (pin): Eastern Rhodopes, Haskovo district, Chernichino vill., 41°35.35'N, 25°50.91'E, 647 m, 23 Apr. 2021, leg. A. Lapeva-Gjonova (MNHW); • 5 w. (pin): same locality as previous, 15. Nov. 2025, leg. A. Lapeva-Gjonova (BFUS: from BFUS -I-AG 003196 to BFUS -I-AG 003200); • 5 w. (pin): Eastern Rhodopes, Kardzhali district, Maslinovo vill., 41°46.03'N, 25°32.56'E, alt. 362 m, 03 June 2025, leg. A. Lapeva-Gjonova (MNHW). Other material. Bulgaria • 3 w. (pin): Eastern Rhodopes, Kardzhali district, Oreshari vill., 41°36.59'N, 25°43.04'E, alt. 111 m, 22 Apr. 2014, leg. A. Lapeva-Gjonova (BFUS: BFUS -I-AG 000165, BFUS -I-AG 003173, BFUS -I-AG 003174, BFUS -I-AG 003176); • 1 g., 2 w. (pin): Eastern Rhodopes, Haskovo district, Chernichino vill., 41°35.35'N, 25°50.91'E, alt. 647 m, 23 Apr. 2021, leg. A. Lapeva-Gjonova (BFUS: from BFUS -I-AG 003183 to BFUS -I-AG 003185); • 10 w. (pin): same locality as previous, 14 Sept. 2025, leg. A. Lapeva-Gjonova (BFUS: from BFUS -I-AG 003186 to BFUS -I-AG 003195); • 7 w. (1 EtOH / 6 pin): Eastern Rhodopes, Kardzhali district, Maslinovo vill., 41°46.03'N, 25°32.56'E, alt. 362 m, 03 June 2025, leg. A. Lapeva-Gjonova (BFUS: BFUS -I-AG 003169; from BFUS -I-AG 003177 to BFUS -I-AG 003182). Etymology. The name refers to the ancient Thracian state of Odrysia, whose geographical extent included the area where the new species was found. The name is formed as a first-declension plural noun. Diagnosis. Messor odrysarum sp. nov. is assigned to the Messor structor group based on well-developed head and mesosoma sculpture, dense pilosity with erect mesosoma setae, absence of a true psammophore, and confirmed by COI analysis. The new species is most closely related to the Balkan-Anatolian species M. oertzeni, as indicated by the following characteristics: the longer antennal scape (SL / HW of 0.89 ± 0.05 in major workers and 1.09 ± 0.02 in gynes), the straight posterior head margin, the distinctly angulate propodeum in major workers, and the COI genetic distance of 5.72 %, which is the smallest compared to other species in the genus from the region. Workers of Messor odrysarum sp. nov. differs from M. oertzeni, in their smaller body size, uniform black colouration, narrowed head posterior to the eyes, more irregular sculpture on the head and promesonotum, and longer, denser setae on the head and mesosoma, but sparser on the metasoma. The gyne of M. odrysarum sp. nov. can be distinguished from M. oertzeni by its smaller size, uniformly black body colour and less regular sculpture on the occipital part of the head and dorsal mesosoma. The new species is currently known from the East Rhodopes in Bulgaria, while M. oertzeni is more widely distributed across the eastern Balkans and Anatolia. Description. Major workers (N = 20). Measurements: HL 1.99 ± 0.15 (1.73–2.24); HW 2.01 ± 0.19 (1.64–2.31); HL / HW 0.99 ± 0.03 (0.92–1.06); SL 1.78 ± 0.10 (1.62–1.93); SL / HW 0.89 ± 0.05 (0.80–0.99); EL 0.38 ± 0.04 (0.32–0.45); MW 1.30 ± 0.11 (1.09–1.48); PSL 0.30 ± 0.04 (0.25–0.38); PTL 0.70 ± 0.06 (0.57–0.82); PTH 0.55 ± 0.04 (0.48–0.62); PTH / PTL 0.79 ± 0.05 (0.70–0.86); WL 2.62 ± 0.19 (2.37–2.95); HFL 2.45 ± 0.15 (2.18–2.66); HFL / WL 0.93 ± 0.02 (0.90–0.99). Colour. Entire body shiny black, except for lower part of the genae, mandibles, antennal condyle, tip of last antennal segment, and joints of legs and tarsi, which are reddish. Head. Almost squared, HL / HW 0.99, sides slightly converging towards posterior margin, latter straight. Anterior clypeal margin slightly convex, finely crenulate, without median emargination, with a row of 8 long marginal, yellowish setae. Clypeus without appressed pubescence, with few short, erect setae. Central plate of clypeus and clypeal alae with longitudinal rugae without median keel, interspaces smooth, shiny. Eyes small and broadly oval (mean EL 0.378 mm). Frontal triangle shallowly impressed, with several longitudinal rugae and smooth interspaces, shiny. Frontal carinae extend beyond frontal lobes and merge with one of antennal semicircular rugae. Frons narrow, approximately 0.25 width of head at narrowest point. Antennal fossa deep and completely surrounded by semicircular rugae, its surface smooth and shiny. Head with longitudinal striation on genae and frons and with more irregular sculpture, being mixture of microreticulate and rugulose structures on vertex. Narrow median band from vertex to frons smooth. Anterior surface of head covered with short, sparse, yellowish appressed setae, while long, decumbent to semierect setae cover its entire surface. Ventral part of head and inner margin of mandibles with numerous, semierect setae of various lengths, straight to occasionally C-shaped, which do not form distinct psammophore. Antennae elongated, 0.80–0.99 as long as head width. At base, scape strongly extended, forming rounded outer and subangulate inner angles. In frontal view, apical part of scape slightly curved with preapical constriction. Funiculus distinctly longer than scape, pedicel moderately elongated, approximately 2.2 × as long as wide at apex, flattened dorsoventrally, approximately 0.87 × as long as segments 2 and 3 combined and 1.75 × as long as segment 2. Scape with diffused microreticulation, shiny, covered with long, dense, yellowish setae, decumbent to subdecumbent. Mandibles rounded, shiny surface with deep grooves with a few yellow setae, cutting edge in large majors without teeth or with serrulate edge. Mesosoma. Moderately long, approximately twice as long as wide. Promesonotum convex in lateral view with mesonotum slightly bulging above pronotal plate. Pronotum rounded at sides. Propodeum lower than promesonotum, flat dorsally and distinctly angulate; in largest workers with subangulate denticle; posterior slope oblique. Pronotum anteriorly and dorsally with distinct irregular reticulate sculpture, laterally with longitudinal rugae, interspaces smooth and shiny. Elevated dorsal plate of mesonotum with transverse rugae; sides reticulate; mesopleura with sharp, sparsely arranged, vertically positioned rugae; interspaces microreticulate and shiny. Propodeum dorsally and on posterior slope with sharp transverse rugae; metapleural area with sharp longitudinal rugae; interspaces with diffuse microreticulation; metapleurum and posterior face of propodeum partly smooth and shiny. Promesonotum, dorsal part of propodeum and mesometapleural sulcus with short, sparse, yellowish appressed setae. Numerous long, dense, erect setae cover mesosoma dorsally, longer on promesonotum and twice shorter on propodeum. Waist and gaster. Moderately long peduncle with moderately high triangular node, thin, PTH / PTL 0.79. Peduncle, and base of node with distinct reticulate sculpture, anterior face concave with distinct microreticulation, slightly dull, sides and posterior face of node strongly microreticulate with several irregular rugosities. Dorsal petiole angulate in lateral view, upper margin shallowly emarginate, top and lateral sides of node with 10–15 erect setae. Postpetiole rounded in lateral view, globular in dorsal view, 1.1–1.3 × as wide as the petiole; surface microreticulate; sides and posterior face with several sharp, irregular to transverse rugosities. Dorsal sclerite with c. 20 long erect setae; sternal sclerite with c. 10 shorter erect setae. First gastral tergite entirely microreticulate; surface shiny, bearing extremely sparse and short appressed setae together with long, semierect setae, the longest reaching 0.29 in length. Legs. Elongate, femora moderately swollen centrally, tibiae moderately widened apically, mid and hind tarsi longer than tibiae. Whole femora microreticulate, dorsally and laterally covered with dense and long, decumbent and subdecumbent and ventrally semierect to erect setae. Tibiae covered with dense and long decumbent to semierect setae. Smallest workers (N = 15). Measurements: HL 1.01 ± 0.07 (0.89–1.15); HW 0.95 ± 0.07 (0.83–1.08); HL / HW 1.07 ± 0.02 (1.04–1.13); SL 1.03 ± 0.08 (0.92–1.17); SL / HW 1.09 ± 0.02 (1.04–1.12); EL 0.20 ± 0.02 (0.17–0.25); MW 0.64 ± 0.04 (0.57–0.70); PTL 0.39 ± 0.03 (0.31–0.43); PTH 0.29 ± 0.02 (0.27–0.33); PTH / PTL 0.76 ± 0.04 (0.71–0.85); WL 1.40 ± 0.09 (1.23–1.53); HFL 1.20 ± 0.10 (1.02–1.37); HFL / WL 0.86 ± 0.05 (0.68–0.91). Colour. Same as major workers, black, the antennae, legs, waist and gaster appear dark brown. Head. Slightly more elongated (HL / HW mean 1.07) and more rounded in frontal view than major workers, softly converges posterad behind eyes, posterior head corners rounded, and occipital margin straight. Antennae elongated; scape 1.04–1.12 as long as head width, covered with long, dense erect setae. Sculpture of head less developed than in major workers, with striation on frontal area and genae, vertex and occipital corners with microreticula