A new species of the Gnamptogenys Mordax subgroup (Hymenoptera: Formicidae), with an Identification key to the species within the subgroup

T We describe, Gnamptogenys rugimala n. sp , a very distinct new species of the ectatommine genus Gnamptogenys, from specimens collected in forests of southeastern Brazil. We provide some data about G. rugimala n. sp occurrence and ecology as well as a species identification key for the mordax


Introduction
The ectatommine ant genus Gnamptogenys Roger, 1863 has a distribution ranging from the Neotropics to the southern Nearctic and from Indomalaysia to Australia. They are usually found in the leaf litter of tropical and subtropical forests, commonly nesting in subterranean chambers or in rotten logs. In his revision of the New World Gnamptogenys, Lattke (1995) proposed six groups and eleven subgroups. One of these groups is the mordax group, which is divided into four subgroups. The mordax subgroup, which is currently represented by five species, is defined by the following suite of characters: subfalcate mandibles with a smooth and shining dorsal surface; a concave anterior clypeal margin with rounded lamellar sides; a well-impressed metanotal groove; a slightly pedunculate petiolar node; and a subpetiolar process that projects anterad (Lattke, 1995).
The species G. boliviensis Lattke, 1995;G. continua (Mayr, 1887); G. interrupta (Mayr, 1887); G. mordax (Smith, 1858) and G. stellae Lattke, 1995 considered collectively range from Veracruz (central Mexico) to southeastern Brazil (Guénard et al., 2017). Longino (1998) found consistent morphological differences within species determined as G. mordax and G. interrupta, a situation that suggests the presence of cryptic species within each nominal species. Little is known of their natural history except for their preference for nesting and foraging in the leaf litter and decomposing wood on the ground (Lattke, 1990). Midden contents from a few nests of G. mordax and G. interrupta in Venezuela suggest at least some preference for preying upon beetles (Lattke, 1990).
During the routine curation of Gnamptogenys samples in the Museu de Zoologia da Universidade de São Paulo (MZSP) we found two conspecific specimens from two different localities in southeast Brazil belonging to the mordax species subgroup with a unique combination of character states not seen in any other of the known species. We describe this new species (Fig 1) and present an identification key to species of this subgroup. Biosistemática de Formigas, Curitiba, PR, Brasil

Material and methods
Morphological terms used follow Keller (2011) for general morphology, Harris (1979) for sculpturing, and Wilson (1955) for pilosity. Measurements were made using an ocular micrometer on a Zeiss  Stemi SV 6 stereo microscope and follow those of Lattke (1995).
HL ( For comparative purposes, we examined workers of two mordax subgroup species with the following data. We also examined high-resolution pictures of the types of four species, as well as those of two workers of G. stellae, all available on AntWeb (2019). Specimen identifier numbers as follows: G. boliviensis, CASENT0900556 (Photo: Ryan Perry); G. continua, CASENT0178676 (Photo: April Nobile); G. interrupta, CASENT0915912 (Photo: Anna Pal); G. mordax, CASENT0907188 (Photo: Will Ericson), CASENT0900547 (Photo: Ryan Perry); G. stellae, CASENT0281227 (Photo: Estella Ortega), INB0003662341 (Photo: Estella Ortega). Etymology. The species epithet is derived from the Latin noun for jawbone, mala, and the Latin noun for crease or wrinkle, ruga.

Gnamptogenys rugimala
Diagnosis. Within the mordax subgroup this species is recognized by the dorsum of the mandible with striae/rugae on at least one fourth of the mandible length; relative small eye size (OI < 11); broad pronotal-anepisternal suture; second gastral tergite smooth and shining.
Head in dorsal view rectangular, posterior cephalic margin slightly concave, lateral margin straight to weakly convex, head slightly wider anteriorly than posteriorly; clypeus with anteromedian projection slightly wider than distance between frontal lobes, anterior margin of projection sinuous with broad median concavity and lateral convexity that extends posteriorly to rest of clypeus, clypeal lamella very narrow, best seen in anteroventral view of clypeus. Labrum with median concavity at apex, dorsal surface transversely imbricate, prementum smooth and shining, stipes with median rugulose sulcus; hypostoma finely imbricate. Cephalic dorsum and vertex longitudinally costate with sparse piligerous punctae, individual costula smooth and shining. Scape dorsoventrally flattened, failing to reach posterior cephalic border by slightly more than one apical width, dorsum smooth and shining with sparse punctulae. Mandible elongate, semifalcate, with broad basal convexity, internal and masticatory margins only distinguishable from one another by absence of teeth on internal margin, masticatory margin with series of low blunt denticles, better observed in oblique ventral view of mandible; dorsum with narrow band of rugulae and elongate punctae bordering masticatory margin from base to midlength of mandible, medioapically mostly smooth. Cephalic vertexal face concave, meeting dorsum at blunt angle; eye small, 6-8 ommatidia long, set just posterad to midlength of lateral cephalic margin in lateral view; ventral cephalic face with broadly diverging costulae.
Petiole with short peduncle; in lateral view low, subquadrate, anterior margin oblique, broadly concave, dorsal margin slightly convex, posterior margin vertical, broadly convex; anterior face rugose, laterally and dorsally with longitudinal costae; posterior face narrow and transversely costate. Subpetiolar process in lateral view trapezoid, with longest base attached to sclerite, anterior margin broadly convex, ventral margin broadly concave and posterior margin almost straight; surface irregularly areolate. Anterior face of abdominal tergite III mostly smooth, dorsal and lateral faces longitudinally costate; abdominal sternite III with slightly weakened costae laterally, smooth and shining centrally with sparse punctae; rest of gastral segments smooth and shining with sparse punctulae. Procoxa transversely costate in lateral view, meso and metacoxa rugose; metacoxa with low dorsal lobe. Tibiae and femora mostly smooth and shining with sparse punctulae; probasitarsal notch with dense row of hairs and single median seta.
Head, thorax, dorsum of petiole and gaster without basal pubescence, with sparse erect to suberect yellow hairs, abundant pilosity on posterior gastral segments. Dorsum of antennal scape mostly devoid of pilosity except for posterior and anterior margins with subdecumbent hairs shorter than scape width. Antennae and legs yellowish brown to ferruginous; mandible brown; head, thorax and abdomen ferruginous brown to dark brown, sides lighter colored than dorsum, head dark brown to black.

Geographic range
This species is only known from the states of São Paulo and Paraná, southeastern Brazil.

Biology
Both ants were captured using Winkler extractors. Both of them came from an Atlantic forest region, classified as Cfb on Köppen climate classification, with annual rainfall of 1,550 mm and average temperature of 17°C through the year (Alvares et al., 2014). According to IBGE (2019), these areas are defined as Floresta Ombrófila Densa Montana in association with secondary vegetation. This vegetation is found in altitudes ranging from 400 to 1.000 meters and generally has a thin soil layer, bearing trees of 20 meters height on average, with small leaves and thin trunks. Both specimens were found at an approximate altitude of 850 m

Discussion
Gnamptogenys rugimala is the only species in the subgroup with rugae on the mandibular dorsum. Gnamptogenys continua and G. boliviensis are very similar to this species, but present costulae on the second gastral tergite, and both species have a relatively larger eye diameter when compared with G. rugimala. The anterior clypeal margin of G. continua is weakly sinuous compared with G. rugimala. Gnamptogenys continua has a smooth and shining vertex, while in G. rugimala it is costate. The anterior pronotal face is mostly smooth and shining in G. continua, differing from the rugose face present in G. rugimala. Gnamptogenys continua has the metapleuron totally costulate, differing from G. rugimala which has the anterior metapleuron mostly smooth and shining. Gnamptogenys continua presents a reduced anepisternum, but it is distinct and does not present a broad pronotal-mesopleural suture, present in G. rugimala. Finally, G. continua bears a distinct anterolateral lobe on the propodeal declivity, poorly developed on G. rugimala. Compared with G. boliviensis the dorsal head sculpturing is very distinct, G. boliviensis presents a great number of striae, while G. rugimala presents thick costulae on its dorsum head. The pronotal-anepisternal suture in G. rugimala is broad, different from the narrow one present in G. boliviensis. Gnamptogenys interrupta and G. stellae do not have dorsal lobes on the metacoxa, readily separating them from G. rugimala before even considering other morphological characters. Gnamptogenys mordax is easily distinguishable by the presence of a large cuticular projection on the metacoxal dorsum. Besides that, G. mordax has much larger compound eyes (OI > 18) placed slightly dorsolaterally on its head. Gnamptogenys rugimala presents smaller and laterally placed compound eyes that are hard to see in a full face view.