Leptanilla hypodracos Wong & Guenard

Wong, Mark K. L. & Guenard, Benoit, 2016, Leptanillahypodracos sp. n., a new species of the cryptic ant genus Leptanilla (Hymenoptera, Formicidae) from Singapore, with new distribution data and an updated key to Oriental Leptanilla species, ZooKeys 551, pp. 129-144 : 131-138

Taxon classification Animalia Hymenoptera Formicidae

Leptanilla hypodracos Wong & Guenard sp. n. Figs 1, 2, 3, 4, 5, 6, 7

Holotype.

Worker from SINGAPORE, Central Catchment Nature Reserve , 1°21.3'N; 103°48.9'E, ca. 55m asl, 15.VI.2015, via subterranean pitfall trap, leg. Mark K. L. Wong, label “MW150615-1.1” deposited in LKCNHM.

Paratypes.

Two workers in total, all with the same data as holotype (deposited at SBSHKU), labelled “MW150615-1.2” and “MW150615-1.3”. Unfortunately these specimens were incomplete when collected, with only a head present for one specimen and the second specimen missing part of its antennae and legs. Both specimens were probably damaged by other ants present in the subterranean pitfall trap during collection. The second specimen was very fragile and was damaged during specimen manipulation (breakage at the propodeum/petiole junction). The broken parts were kept in ethanol while the head and mesosoma were mounted for measurements.

Measurements and indices.

Holotype.HL 0.35 mm; HW 0.27 mm; MaL 0.16 mm; SL 0.19 mm; EL 0 mm (eye absent); WL 0.44 mm; PNW 0.18 mm; PNH 0.12 mm; MW 0.11 mm; PTL 0.10 mm; PTW 0.06 mm; PTH 0.10 mm; TL 1.73 mm (stinger not included); PPL 0.09 mm; PPW 0.08 mm; PPH 0.12 mm; CI 78, SI 69, MaI 57, PI 60, PPI 90, PPHI 70.

Paratype (n = 1). HL 0.35 mm; HW 0.27 mm; MaL 0.15 mm; SL 0.19 mm; WL 0.44 mm; PNW 0.18 mm; PNH 0.12 mm; MW 0.11 mm; CI 76, SI 69, MaI 54.

Worker description.

Head. Head longer than wide (CI = 76-78). In full-face view, posterior margin of head straight to slightly concave. Lateral margins of head slightly convex with posterior margins rounded. Eyes absent. Anterior clypeal margin extending forward with two rounded lobes anterolaterally and slightly concave on its anteromedian portion (Fig. 1B). Median portion of clypeus raised. Mandibles short relative to head (MaI = 54-57) armed with three teeth. Mandibles with a distinct ridge on their basal margin (Fig. 2B). Apical tooth large and acute followed by two smaller teeth; with the basal tooth significantly smaller, blunt and pointing inward. Antennal insertion exposed. Antennae with 12 segments. Scape inflated in its median portion, dorsally concave, and extending over the mid-point of head. Pedicel distinct from the scape and flagellum by marked constrictions. Flagellum incrassate with the last antennal segment distinctly longer than the previous flagellomeres, about the size of the previous two segments.

Mesosoma. In lateral view, mesosoma with a continuous straight appearance with the exception of a well-marked interruption of the promesonotal suture (Fig. 3B). In dorsal view, pronotum wider than posterior portions of mesosoma, especially on its anterior half (Fig. 4B). In profile view, a distinct sulcus of fine striae separates the pronotum from the propleuron extending from the dorsal portion of the neck and reaching the inferior part of the promesonotal suture just above the coxal junction (Fig. 5B). In profile view, both anterodorsal and anteroventral parts of pronotum rounded with the latter droplet-shaped. Mesonotum and propodeum with similar width and without obvious inflated portion. Promesonotal suture deeply impressed and clearly visible in both dorsal and profile view. Metapleural gland bulla large and elongate, nearly as large as the maximum width of hind coxa (Fig. 6B). Posterior part of propodeum forming the propodeal declivity nearly at right angle with rounded edges.

Metasoma. In profile view, dorsal and ventral portion of petiolar node markedly convex, rounded without acute portion nor subpetiolar process. Dorsal margin of postpetiole convex and rounded. Dorsal margin of the postpetiolar node lower than the maximal height of the dorsal margin of the petiolar node. Sternopostpetiolar process well developed and rounded. In dorsal view, petiolar node longer than wide (PTL = 0.10 mm, PTW = 0.06 mm) while postpetiole more rounded (PPL = 0.09 mm, PPW = 0.08 mm).

Sculpture. Sculpture absent on most of the body. Most of the body with a slick and shiny appearance with the exception of the neck with clear transversal striae (Fig. 7B). Hair insertion on head giving an impression of the presence of small punctuations.

Pubescence. Pubescence present on most of the body, especially on dorsal parts. Antennae and mandibles with numerous erect to suberect long hairs.

Coloration. Head, thorax and fore coxa with a dark amber colour, while petiole, postpetiole and most of the gaster slightly lighter. Antennae, legs (with the exception of the fore coxa) and tip of the gaster with a much lighter yellow coloration.

Castes. Male and female unknown.

Etymology.

The species epithet is derived from a combination of the Latin terms for ‘under’ and ‘dragon’, in reference to the slender, dragon-like appearance of this subterranean predator. The species epithet is a noun, and thus invariant.

Distribution.

Southeast Asia. Only known from Singapore.

Ecology.

Leptanilla hypodracos was collected from a well-shaded patch of tropical low-lying old secondary forest with a high density of leaf litter and woody debris on the forest floor. As with other Leptanillinae, Leptanilla hypodracos presents a hypogaeic lifestyle and was collected in a baited subterranean pitfall trap at a depth between 10-15 cm. Colony size and structure is unknown. Although the specimens were collected in a trap containing tuna bait, it is presently unclear as to whether Leptanilla hypodracos were recruited to the bait, since other Leptanilla species have previously been suggested to be specialist predators of geophilomorph centipedes ( Masuko 1990) and have yet to demonstrate any scavenging habits. In contrast, other species present at the same bait were collected in high densities (>100 individuals each), and these belonged to mass-raiding species of Dorylus Fabricius, 1973 and generalized foraging species of Carebara Westwood, 1840.

Remarks.

Based on a morphological examination, Leptanilla hypodracos is close to several other Leptanilla from the Oriental region, namely Leptanilla escheri Kutter, 1948, Leptanilla butteli Forel, 1913, and Leptanilla thai , but is most similar to Leptanilla clypeata .

Leptanilla hypodracos differs from Leptanilla escheri in the anterior margin of the petiole in profile view, which is rounded in Leptanilla hypodracos but more angular in Leptanilla escheri while in dorsal view, Leptanilla hypodracos displays a long and narrow petiole (PI = 47, PPI = 83) that contrasts with the rounded petiole which is as wide as it is long in Leptanilla escheri (PI = 87-120, PPI = 117-145). In dorsal view Leptanilla hypodracos also has a narrower mesosoma than Leptanilla escheri . Furthermore, as records of Leptanilla escheri are restricted to southern Indian highlands where the elevation ranges from 1250 to 1775m asl, and Leptanilla hypodracos was collected in a tropical lowland forest of Singapore at an elevation of 55m asl, it is conceivable that the two species occupy differing ecological niches.

Similar species reported from the Malay Peninsula include Leptanilla butteli from West Malaysia and Leptanilla thai from Southern Thailand. However, Leptanilla hypodracos is distinguished from these species in having a more rounded petiolar node and a less inflated petiole. In comparison, both Leptanilla butteli and Leptanilla thai possess square-shaped petiolar nodes with rounded angles and more inflated petioles ( Baroni Urbani 1977). In full-face view, the extension of the anterior clypeal margin is present in Leptanilla hypodracos but absent in Leptanilla butteli . In terms of overall size, Leptanilla hypodracos (TL = 1.73 mm) is larger than both Leptanilla butteli (TL = 1.40-1.50 mm) and Leptanilla thai (TL = 1.40-1.50 mm), although the head size of Leptanilla thai (HL = 0.36 mm, HW = 0.27 mm) ( Baroni Urbani 1977) is comparable to that of Leptanilla hypodracos (HL = 0.35 mm, HW = 0.27 mm).

Leptanilla hypodracos presents the most similarities with Leptanilla clypeata from Java, Indonesia, but can be distinguished from the latter by a suite of distinct characteristics. We also provide a new set of complete measurements for Leptanilla clypeata (see below). The primary difference is observed in dorsal view and pertains to the shape and size of the petiolar node and postpetiole. In Leptanilla hypodracos , the petiolar node is nearly twice longer than wide (PI = 60, PTL = 0.10 mm, PTW = 0.06 mm) and the postpetiole is longer than wide, and also more rounded (PPI = 90, PPL = 0.9 mm, PPW = 0.08 mm). However in Leptanilla clypeata , the petiolar node is almost as wide as long (PI = 82, PTL = 0.11 mm, PTW = 0.09 mm in Ito et al. 2001; new measurements PI = 100, PTL = 0.10 mm, PTW = 0.10 mm), while the postpetiole is distinctly wider than long (PPI = 137, PPW = 0.11 mm, PPL = 0.08 mm in Ito et al. 2001; new measurements PPI = 133, PPW = 0.12 mm, PPL = 0.09 mm) contrary to Leptanilla hypodracos . Hairs on the posterodorsal subpetiolar process of Leptanilla hypodracos are sparser and shorter than in Leptanilla clypeata . The posterodorsal corner of the prodeum also more angular in Leptanilla hypodracos while being more rounded in Leptanilla clypeata . In full-face view, the mandibles of Leptanilla hypodracos display a long and well-defined basal tooth, however this character is neither visible in the observed specimen of Leptanilla clypeata nor on the figures of Ito et al. (2001, Figures 7A, C).

In addition to the characteristics above, there are several other differences between Leptanilla hypodracos and Leptanilla clypeata , which should be confirmed with future collection of both species. The head of Leptanilla hypodracos (CI = 76-78) is slightly narrower than that of Leptanilla clypeata (CI = 82 in Ito et. al. 2001, and CI = 84 with our measurements below) (Fig. 1). In profile view, the metanotal groove appears more deeply impressed in Leptanilla hypodracos than it does in Leptanilla clypeata . In full-face view, the anterior part of the clypeal projection is slightly concave to straight in Leptanilla hypodracos but deeply concave in Leptanilla clypeata . Lastly, in dorsal view the pronotum of Leptanilla hypodracos (PNW = 0.18 mm) is narrower than that of Leptanilla clypeata (PNW = 0.20 mm).