Perissomyrmex nepalensis, Radchenko, 2003

Radchenko, Alexander, 2003, Perissomyrmex nepalensis sp. nov. - new evidence of Old World origins for the genus (Hymenoptera, Formicidae), Entomologica Basiliensia 25, pp. 13-22 : 14-18

Perissomyrmex nepalensis sp.nov.

Material examined. Holotype worker: Nepal, Kosi, Chanki , 27°H'-12'N, 87°27'-28'E Alt. 2600-3000 m, No. 221 c , 22-24. vi.2001 ( NHMB expedition in Nepal, 2001) . Paratypes: 1 worker, same site, date and collectors ( NHMB) ; 3 workers: India, W. Bengal, Darjeeling , Tiger Hill, 2450 m, 28.viii. 1997 (G. Cuccodoro) ( BMNH) .

Workers (Figs 1-10). Head clearly wider than long, distinctly broadened anteriorly (in holotype worker; but in paratype workers it is much less broadened; compare Figs 1 and 9, and CWI in Table 1 ), with rounded occipital corners and more or less straight, at most very shallowly concave, occipital margin. Anterior clypeal margin prominent medially, with a pair of relatively long medial lobes, and two much smaller lateral denticles. Mandibles elongate, with unwidened masticatory margin and with four teeth: three on masticatory margin and one on inner margin, separated from the others by long diastema. Frontal lobes not developed, antennal articulations exposed. Eyes small, more or less rounded, situated approximately at the mid-point of the sides of head. Ocelli absent. Antennal scape very feebly curved at the base, quite long, reaches distinctly beyond occipital corners. Frontal carinae short, feebly curved, merging into the costulae, which reach occipital margin (this feature is not particularly clear; in the holotype worker the right carina curves outwards to merge into the costula, which surrounds the antennal socket). Antennal sockets surrounded by concentric costulae.

Head dorsum with quite coarse, longitudinal, slightly sinuous costulae, which are distinctly divergent towards occipital corners; frons between frontal carinae level with the eyes, having 10-11 costulae. Frontal triangular and clypeus smooth. Mandibles with fine longitudinal costulae and rugosity, relatively coarser on basal half of the mandibles. Whole surface of the head between costulae with a very fine, superficial microsculpture (visible under magnification not less than x 100) appears shiny. The palp formula is most probably 5,3 (previous authors gave no palp formula for Perissomyrmex species; unfortunately the labial and maxillary palps in all the specimens investigated are not clearly visible without dissection and making slides).

Alitrunk with convex promesonotal dorsum, which is distinctly raised over propodeal level. Promesonotal suture well developed, especially on the sides of alitrunk, but also distinctly visible from above. Posterio-lateral corners of pronotal dorsum forming rounded protuberance-like processes (viewed from above). Metanotal groove deep. Propodeal spines quite long, sharp, directed backwards and slightly upwards at an angle of about 45°, less or more divergent (viewed from above; compare Figs 5 and 10, and ESDI in Table 1 ). Propodeal lobes narrowly rounded. Petiole with long peduncle and strongly concave anterior surface, its node quite high, with rounded dorsum, without horizontal plate. Postpetiole quite high, with narrow, more or less cuneiform node, of which anterior surface slightly convex and posterior surface slightly concave (viewed in profile). Middle and hind tibiae without spurs.

Propleurae with coarse, regular, more or less straight, longitudinal costulae, which are broken or completely absent on anterio-dorsal surface of pronotum. Lower part of mesopleurae smooth; both upper part of mesopleurae and sides of propodeum with short, somewhat sinuous, irregular longitudinal costulae. Distal part of pronotal dorsum, mesonotal- and propodeal dorsum with similar irregular costulae; central part of propodeal dorsum and its declivity between spines smooth. Whole surface between costulae smooth and shiny (similar to that of the head). Petiole and postpetiole almost completely smooth and shiny, only distal part of postpetiole with short irregular rugae. Gaster smooth and shiny.

Head with very abundant and long, thin standing hairs, curved at the tips; anterior clypeal margin with very long setae. Alitrunk also with abundant hairs, which are even longer than hairs on the head. Antennal scape with hairs of different length, but longest ones approximately 1.6 times longer than maximum width of scape. Femora and tibiae with similar hairs, longest hairs on the hind tibiae 1.4-1.5 times longer than maximum width of tibia. Tarsi with long hairs on their outer margin (longest hairs 3.5-3.6 times longer than maximum width of the tarsus), and with much shorter, "brush-like", dense subdecumbent hairs on their inner margin. Waist and gaster with numerous, long, slightly curved hairs. Whole surface of the body without decumbent pilosity.

Head, alitrunk and waist dark brownish-black to black, gaster dark brown, appendages distinctly lighter, brownish-yellow, clypeus and mandibles reddish-brown.

Queens and males as yet unknown.

Measurements (in mm; data for holotype are in brackets): HL 1 0.82-1.07 (1.00), HL2 0.91-1.14 (1.06), HW 1 0.89-1.17 (1.08), HW2 0.93-1.19 (1.14), SL 0.83-1.00 (0.99), OL 0.10-0.12 (0.10), AL 1.04-1.25 (1.20), PL 0.43-0.47 (0.46), PPL 0.24,0.29 (0.28), PH 0.29-0.34 (0.33), PPH 0.29-0.34 (0.32), PW 0.17-0.19 (0.18), PPW 0.22-0.26 (0.24), ESL 0.17-0.29 (0.29), ESD 0.30-0.40 (0.33), HTL 0.74-0.95 (0.91), PNW 0.56-0.68 (0.63).

Indices see in Table 1 .

Ecology is unknown. All specimens were collected from pitfall traps at an altitude of between 2450 and 3000 m.

Name derivation. Species named after Nepal, the country in which the holotype was found.

Comparative analysis

Although P. monticola shares many features with both previously described species, it clearly differs from them by a complex of morphological characters.

It is similar to P. snyderi in the long, outstanding hairs on the body and appendages, which in P. snyderi are less abundant on the head margins, but even longer on antennal scape and legs (in P. nepalensis sp.nov. longest hairs approximately 1.6 times longer than maximum width of the scape versus about 1.7 times in P. snyderi ; respectively, on the hind tibiae longest hairs 1.4-1.5 times longer than maximum width of the tibia versus 1.7 times, and on the hind tarsi longest hairs 3.5-3.6 times longer than maximum width of the tarsus versus 4-4.5 times) (compare also Figs 1, 4-8 and 11, 13-17). In contrast, P. monticola has much less abundant outstanding hairs on the head, and much shorter ones on appendages: antennal scape with abundant, but very thin, fine hairs, which are not longer than maximum diameter of the scape; longest hairs on hind tibiae subequal or at most slightly longer than maximum width of the tibia, and on the hind tarsi longest hairs not more than 3 times longer than maximum width of the tarsus (compare also Figs 1, 4-8 and 18, 20-24).

In body colour, P. nepalensis sp.nov. is similar to P. snyderi , but has brownishyellow appendages (much lighter than body) compared with the much darker brown of the latter species. On the other hand, the body colour of P. monticola is somewhat lighter than that of both other species and the appendages are even lighter (quite bright yellow) than in P. nepalensis sp.nov.

The shape and length of the central pair of clypeal lobes in P. nepalensis sp.nov. is similar to that in P. monticola , but in P. snyderi they are much shorter (compare Figs 1, 2, 18, 19 and 11, 12).

The sculpture of the head dorsum of P. nepalensis sp.nov. is similar to that of P. monticola , only in the latter the frontal carinae curve outwards to merge into the costulae, which surround the antennal socket (at least in the investigated paratype specimen). Costulation on head dorsum in P. snyderi is somewhat denser - the frons between frontal carinae, level with the eyes, has 14 costulae versus 10-11 in P. nepalensis sp.nov.

The sculpture of the alitrunk differs between all three species. P. monticola differs from both the others in much less developed sculpture on mesopleurae and sides of propodeum, while P. nepalensis sp.nov. differs from the two other species in broken transversal costulation on the anterio-dorsal surface of pronotum, and by more irregular sculpture on the alitrunk dorsum (compare Figs 4, 5, 13, 14, 20 and 21).

P. nepalensis sp.nov. has a similarly shaped petiole to that of P. monticola , while the petiolar node of P. snyderi is more widely rounded, with a more or less distinct, convex dorsal plate (compare Figs 4, 20 and 13).

Smith (1947) gave no measurements and indices in his description of P. snyderi . I therefore measured the holotype and in order to ensure comparability I also re-measured a paratype worker of P. monticola (for indices see Table 1 ):

P. snyderi (holotype worker): HL 1 0.94, HL2 0.98, HW1 0.97, HW2 1.02, SL 0.96, OL 0.14, AL 1.11, PL 0.42, PPL 0.29, PH 0.30, PPH 0.33, PW 0.20, PPW 0.25, ESL 0.25, ESD 0.37, HTL 0.80, PNW 0.60 mm [range of polymorphism of this species shown by Longino & Hartley (1994)].

P. monticola (paratype worker): HL 1 1.03, HL2 1.12, HW 1 1.08, HW2 1.10, SL 0.99, OL 0.13, AL 1.22, PL 0.44, PPL 0.30, PH 0.33, PPH 0.36, PW 0.19, PPW 0.27, ESL 0.31, ESD 0.32, HTL 0.95, PNW 0.66 mm.

A key to identification of Perissomyrmex species

1. Antennae and legs with long, standing hairs (Figs 6-8, 15-17) 2.

Antennae and legs with much shorter standing hairs ( Figs 22-24 ). P. monticola de Andrade, 1993

2(1) Central pair of clypeal lobes short (Figs 11, 12). Sculpture on head dorsum denser, frons between frontal carinae level with the eyes, having not less than 14 costulae (Fig. 11). Appendages dark brown P. snyderi Smith, 1947

Central pair of clypeal lobes long (Figs 1, 2). Sculpture on head dorsum sparser, frons between frontal carinae level with the eyes, having 10-11 costulae (Fig. 1). Appendages brownish-yellow P. nepalensis sp.nov.

In conclusion, I suggest that the discovery of a second species of Perissomyrmex in tropical Asia, which generally more resembles the Neotropical P. snyderi than the Bhutanese P. monticola , supports an Old World origin for this genus, as hypothesised by Baroni Urbani & de Andrade (1993).

Figures

Figs 18-24. Details of structure of P. monlicola de Andrade (paratype worker): 18, head, frontal view; 19, lower part of clypeus; 20, alitrunk and waist in profile; 21, alitrunk and waist from above; 22, antennal scape, lateral view; 23, antennal scape, dorsal view; 24, tibia and first tarsal joint of hind leg. Scale lines 2 mm; short line: Figs 18, 20, 21; long line: Figs 19, 22-23.

Tables

Table 1. Indices calculated for the holotype and paratype workers of the species of the genus Perissomyrmex Smith.

Indices	P. ne palensis sp.nov. holotype paratypes mean			P. snyderi (holotype)	P. monticola (paratype)
Clr	0.93	0.92-0.94	0.93	0.96	0.95
CI2	0.98	0.97-1.02	0.99	1.01	1.04
CWI	1.06	1.02-1.04	1.03	1.05	1.02
SI	0.92	0.82-0.93	0.88	0.99	0.92
OI	0.09	0.10-0.12	0.10	0.14	0.12
Pit	0.39	0.40-0.43	0.41	0.48	0.43
Pl 2	1.39	1.38-1.48	1.41	1.40	1.33
PPI,	0.86	0.90-0.96	0.91	0.86	0.90
PPI 2	0.88	0.83-0.91	0.86	0.88	0.83
ESLI	0.27	0.19-0.25	0.24	0.26	0.29
ESDI	1.14	1.22-1.76	1.40	1.48	1.03