Rhopalothrix mandibularis Guerrero & Grajales, 2024

Guerrero, Roberto J., Grajales-Andica, Andres F., Fernandez, Fernando, Tocora, Maria C., Fiorentino, Gianpiero & Garcia, Delly R., 2024, The ants of the genus Rhopalothrix Mayr, 1870 (Hymenoptera, Formicidae, Myrmicinae) in Colombia, ZooKeys 1191, pp. 129-150 : 129

Rhopalothrix mandibularis Guerrero & Grajales sp. nov.

Figs 2 , 7

Type material.

Holotype. Colombia • 1 worker; Quindío, Armenia, Sena; 4.56931°N, 75.64347°W; 1565 m a.s.l.; 18 Feb. 2020; A.F. Grajales-Andica & D.R. García-Cárdenas legs.; ex sifted leaf litter, gallery forest; CBUMAG:ENT:35947. Paratypes (N = 4). Colombia • 1 worker; same data as for holotype; CIUQ-025287. • 1 worker; Quindío, Armenia, Parque de la Vida; 4.54614°N, 75.65933°W; 1515 m a.s.l.; 8 Oct. 2020; A.F. Grajales-Andica & D.R. García-Cárdenas legs.; ex sifted leaf litter, gallery forest; CIUQ-025288. • 1 worker; Quindío, Armenia, Yulima; 4.5515°N, 75.671°W; 1485 m a.s.l.; 8 Feb. 2020; A.F. Grajales-Andica & D.R. García-Cárdenas legs.; ex sifted leaf litter, gallery forest; CIUQ-025289. • 1 worker; Valle del Cauca, Vda. El Tenjo, Finca La Alejandría; 3.51667°N, 76.16667°W; 1703 m a.s.l.; Aug. 2006; Grupos Hormigas U. V. legs.; ex sifted leaf litter; MUSENUV HOR 008.

Holotype worker measurements.

MdL 0.48, MdbW 0.08, ClyL 0.2, ClyW 0.44, HL 0.67, HW 0.76, WL 0.65, PrnW 0.43, PetL 0.36, PpetL 0.13, PetW 0.19, PpetW 0.31, T4L 0.6, GL 0.68.

Paratype workers measurements

(N = 3). MdL 0.48-0.52, MdbW 0.08-0.09, ClyL 0.19-0.21, ClyW 0.44-0.47, HL 0.65-0.69, HW 0.76-0.78, WL 0.65-0.69, PrnW 0.43-0.45, PetL 0.36-0.38, PpetL 0.13-0.17, PetW 0.19-0.22, PpetW 0.3-0.31, T4L 0.6-0.73, GL 0.67-0.73.

Geographic range.

Colombia.

Diagnosis.

Mandible elongated, much longer (MdL> 0.48) than those of other species in the isthmica clade, mandibles with outer and masticatory margins subparallel to each other and curving inward at tip; labrum with two slender subrectangular lobes, notch deep; propodeal tooth large, acute, right angled to declivitous face of propodeum, infradental lamella poorly developed, forming a thin rim.

Description.

Worker. Head in full-face view broader than long, diamond-shaped, with straight cephalic lateral margins strongly diverging posteriorly, extending below the level of the dorsal crest of the head, at the level of the latter a rounded widening that continues on lateral margins converging towards the rounded posterolateral cephalic corners; wide and concave posterior cephalic margin; front visibly protruding in dorsal view, with an arched transverse carina (= crest), and depression impressed behind the crest. In lateral view, mandible dorsally inclined in relation to head plane (Fig. 7B ); mandible with four to five teeth on masticatory margin as follow: three large equidistant teeth located medially on masticatory margin, basalmost (first) large tooth with a small tooth (sometimes undeveloped) above its base, a middle tooth almost half as long as the previous one, third tooth as long as first, a small fourth tooth as long as 1/3 of first; subapical tooth about twice as long as apical tooth, with denticles at base of both subapical and apical tooth. Trapezoidal labrum as long as broad, with slightly concave sides, subparallel anteriorly, and straight-sided base, labrum with two long blunt subrectangular lobes, with parallel inner faces and deep notch between, length of lobe equal to about 1 /3 of the distance from the base of the notch to the transverse carina at the base of the labrum, Clypeus almost twice as wide as long, with anteroclypeal lobes projecting anterad. Scape just reaching maximum width of head; pedicel and second flagellomere conical towards the base as long as wide, third and fourth flagellomere rectangular wider than long, fifth flagellomere subsquare, last flagellomere finger-shaped tapering apically, as long as the previous four funiculus.

In lateral view, pronotum and mesonotum at the same level, divided by arcuate promesonotal groove and metanotal groove moderately impressed; propodeal dorsum sloping in lateral view. In dorsal view, pronotum with slightly concave anterior margins, narrowing anteriorly to form a distinguishable neck, pronotum with rounded corners at maximum width; in dorsal view, mesonotum wider than long, narrowing posteriorly. Petiole with well-developed peduncle; in lateral view, with straight dorsal face and posteriorly convex ventral face, the latter with a small subpetiolar process projecting anterad as a blunt tooth; petiolar scale rounded in lateral view; postpetiole twice as wide as long (Fig. 7C ).

Short decumbent hairs on surface of head and mesosoma; dorsum of clypeal plate and above posteroclypeal margin with small squamiform hairs. External margin of scape with about 7-9 squamiform hairs similar in size; apex of scape with erect hairs shorter than squamiform ones; funicles with simple subdecumbent hairs. Legs with coxa and femur with few short decumbent hairs; tibia with abundant long, thick semi-erect hairs, and a pair of long flattened hairs located apically on the external surface of each one. About 4-8 squamiform setae on posterior half of first gastral tergite, unspecialized curved hairs scattered over the disc of the first gastral tergite.

Head, mesosoma, petiole and postpetiole shagreened, legs shiny with granular surface, except all tibiae with smooth surface; surface of first gastral tergite finely shagreened. Color reddish brown to ferruginous brown, with yellowish brown distal antennal flagellomeres.

Natural history.

This species inhabits humid forests between 1400 and 1700 m above sea level. The holotype and several paratypes were collected in fragments of humid gallery forest and Guadua (bamboo) forest in the city of Armenia. All known specimens are from Winkler samples of sifted leaf litter.

Etymology.

The name refers to the long mandibles of the worker, a trait not found in any other species in the isthmica clade.

Comments.

This species is placed in the diverse isthmica clade because it shares the two synapomorphies proposed by Longino and Boudinot (2013). This new species, however, has been widely confused in some Colombian collections with R. ciliata due to its similarity in mandibular shape, the shape of the two lobes of the labrum and the depth of the sinus. Rhopalothrix mandibularis can be differentiated from R. ciliata by the absence of squamiform setae on the rostrum, the latter with specialized setae and a flattened surface on the rostrum. Also, mandibles are longer and thinner along their length in R. mandibularis while in R. ciliata they are short and broad; in R. ciliata the tip of the labral lobes can reach up to half the length of the mandible, but in R. mandibularis the anterior margin of the labrum barely reaches the first tooth of the mandible.

Habitus of the worker of Rhopalothrix mandibularis is similar to that of R. stannardi Brown & Kempf, 1960, but the mandible length is remarkably different between the two, as well as the mandible dentition; R. mandibularis has three teeth located towards the middle of the masticatory margin (the most basal tooth is far from the base), while in R. stannardi the three teeth are equidistant, with the most basal tooth starting at the base of the masticatory margin. Another different feature is the infradental lamella, which is very poorly developed in R. mandibularis , while in R. stannardi the lamella is broad and descends almost perpendicularly from the tooth.

Figures

Figure 2. Distribution map of Rhopalothrix species in Colombia.

Figure 7. Rhopalothrix mandibularis sp. nov. Holotype worker (CBUMAG: ENT: 35947) A full-face view B lateral view C mandible distinguishing the teeth of the apical fork; drawing inserted showing the arrangement of the teeth of the apical fork of the mandible D dorsal view. Scale bars: 0.5 mm.