Rostromyrmex pasohensis

A small, cryptobiotic inhabitant of rainforest leaf litter. This rarely collected ant is the sole member of its genus.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Malaysia, Singapore.

Biology
Rosciszewski (1994) - The ants were collected in the litter layer of the forest floor. In one case three specimens were found (1 queen and 2 workers) below a piece of dead wood. Further, 5 workers and 1 queen were found with some brood in a piece of strongly rotten wood. In the third case a similar small colony (6 workers, 1 queen, and some brood) were found in the same microhabitat. The male was bred in captivity. Unfortunately, during a long absence of the author the colony died and the specimens were partly destroyed by mold (and therefore not useful as paratypes).

The ants can easily be overlooked because of their small size, slow movements and dark colouration. They are apparently inhabitants of rotten wood on the ground, forming small, probably monogyne colonies. Their diet is not known. Kept in captivity, the ants were not observed eating the offered honey or dead insects.

Nomenclature

 *  pasohensis. Rostromyrmex pasohensis Rosciszewski, 1994: 163, figs. 1-19 (w.q.m.) WEST MALAYSIA.

With characters of the generic diagnosis Rostromyrmex.

Worker
Holotype — TL 2.17, HL 0.54, HW 0.45, CI 83, SL 0.33, Si 73, PW 0.34, AL 0.59.

Strongly reduced eyes situated at about 1/3 head length on sides of head (measured from mandibular insertions to occipital margin) and measure 0.037 mm in diameter. Length of rostrum in dorsal view is 0.06 mm. Antennal segments 3-6 about 2 times as broad as long, segment 7 slightly broader than long. Apical club more than 2 times longer than remainder funiculus. Sides of head in face view slightly narrowing towards mandibles and rounded towards feebly and shallowly concave occipital margin. Propodeal spines length 0.10 mm. Propodeal declivity almost vertical, slightly sloped dorsad, meeting propodeal dorsum at an angle of about 45° at anterior level of spine bases. A thing, transverse ruga lies between propodeal faces. It may be followed by one or two rugae on propodeal declivity. Metanotal groove in dorsal view at narrowest point of alitrunk and continues laterally as a suture to ventrolateral incision above middle and hind coxae. The suture is interspersed with transverse cross-ribs. Petiolar peduncle relatively long and slender, subpetiolar process (anterior to and below petiolar spiracles) very small. Petiolar node distinct, high, ascending almost vertically, rounded dorsally, slightly broader than long, without a visible step posteriorly. Postpetiole in lateral view slightly lower than petiole, shallowly rounded dorsally, broader than long. Postpetiolar process small and rounded, with two pairs of hairs laterally.

As part of sculpture, small knobs occur on dorsum of head, alitrunk and nodes of petiole and postpetiole. They are readily seen by SEM, less easily under a light microscope. Sculpture on sides of head (including antennal scrobes and base of mandibles) foveate-reticulate with hairs in the pits, sculpture more diluted on ventral side of head capsule. Surface of rostrum with traces of sculpture laterally, moderately shining. Anterolateral portion of clypeus smooth and shining. Scape sculptured dorsally. Mandibles, except laterobasally, smooth and shining. Dorsum of head with irregular sculpture, partly diluted between pits and, particularly towards occiput, equipped with small knobs. Alitrunk sculpture similar, except pits around propodeal spiracle (except ventrad) and on pronotal dorsum small and without hairs. Propodeal declivity, beneath posterior level of spine bases, smooth and shining. Sculpture of nodes almost entirely consisting of knobs, petiolar peduncle foveate. Gaster smooth and shining. Hind parts of coxae and basal parts of femora with weak impressions. Distal parts of femora smooth and shining ventrally, this area flattened and without hairs. Remainder of legs, as well as antennal funiculus, without or with only traces of sculpture, moderately shining. Pilosity moderately dense on whole body, sparse only on meso- and metapleuron and on petiolar peduncle. Gaster with pilosity less dense than on head and alitrunk. Hairs mostly short, approx.. 0.025 mm long, hooked, decumbent to suberect, appressed on legs and antennae. Scattered long hairs present. Maximal hair length on head dorsum 0.036 mm, on alitrunk dorsum 0.086 mm and on gaster 0.049mm. Length of setae on rostrum 0.074 mm, setae between rostrum and projection of anterior clypeal margin 0.098 mm, single median seta 0.074 mm. Body colour uniformly dull red, legs, antennal funiculi, mandibles and rostrum somewhat lighter.

Paratype worker—TL 2.10, HL 0.52, HW 0.43, CI 82, SL 0.31, SI 73, PW 0.32, AL 0.57. One pair of hairs laterally on postpetiolar process. Petiolar node with a small step posteriorly. Other characters as in holotype worker. Two more paratype workers are present in, London.

Queen
Paratype — TL 2.34, HL 0.55, HW 0.47, CI 84, SL 0.34, SI 72, PW 0.36, AL 0.66. Differs from workers as follows. Slightly larger. Eyes well developed, maximal diameter 0.12 mm. Small black spots present around ocelli. Metapleural lobes somewhat weaker developed. Petiolar node provided with small step posteriorly.

Male
Paratype male—TL 1.74 [petiolar node and peduncle measured in combination], HL 0.38, HW [including eyes] 0.40, CI 104.84, SL 0.13, SI 33.85, PW 0.34, AL 0.63.

Median 3 setae on anterior clypeal margin about same length (ca. 0.06 mm), 4 lateral setae are somewhat shorter. Antennal scrobes relatively short (reaching about 2/3 of HL), shallow and poorly delimited, deepened beneath antennal sockets. Frontal carinae not bordering antennal scrobes dorsally, but following their declivity. A weak, carina on ventrolateral margin of head extends from occipital margin to about level of eyes. Eyes large (max. diameter 0.19 mm), occupying most of anterolateral head, extending posteriorly to about level of antennal scrobes. Antennae with all segments longer than wide (pedicellus only slightly so because distally somewhat thickened). Terminal segments slightly longer than the two preceding segments together. Scape relatively short, somewhat flattened dorsoventrally. Head slightly wider across eyes than long. Head in full face view broadest before midlength. Sides of head slightly narrowing towards occiput and rounded towards feebly and shallowly concave occipital margin. Mesonotum almost vertically raised anteriorly, concealing most of pronotum in dorsal view. Metanotum small, strap-like, slightly elevated, just visible in dorsal view beneath scutellum. Dorsal face of propodeum relatively short, declivitous face almost vertical. Two small elevations present on transition between dorsal and declivitous faces of propodeum, thus the faces meet in a sharp angle in lateral view. Sides of propodeum rounded. Petiolar node broadly rounded dorsally, posteriorly descending without a step. Subpetiolar process absent. Postpetiole somewhat flattened dorsally, distinctly wider than long and wider than petiolar node in dorsal view. Postpetiolar process small and rounded, with one pair of hairs.

Fore wing with on cubital cell, radial cell open. Mf1 arises distal of cu-a, lr and r-m absent. Stigma absent, replaced by thickening of the vein. 2r very long, possibly aligned with Rsf4. Hind wing with no closed cells, venation strongly reduced.

Sculpture on head as in female castes, i.e. foveate-reticulate with hairs in the pits. Knobs not recognizable under the light microscope (80x). Dorsum of mesocutum dull, punctate. Punctures shallow, scattered, much more sparse than foveae of head. Scutellum with several large pits. Propodeum foveolate posterolaterally. Pronotum punctate laterally, remainder of pronotum and lateral sides of alitrunk dull with scattered, very shallow pits, absent on smooth and shining anterior and ventrolateral parts of katepisternum. Petiolar peduncle foveolate, laterally with pits extending to ventral and posterior parts of node. Petiolar and postpetiolar nodes from dorsal view dull, sculpture diluted. Pilosity on head including clypeus moderately dense. Hairs decumbent to suberect, mostly short, about 00025 mm long, on vertex and genae longer, up to 0.06 mm. Mandibles with some decumbent to appressed hairs, antennae with dense, decumbent to suberect pilosity. Eyes with short, suberect pilosity. Alitrunk dorsum, sides of petiole and postpetiole, and gaster covered with relatively sparse, appressed to suberect pilosity, occasionally longer hairs present. Scutellum with several long hairs (up to 0.06 mm) which arise from large pits. Remaining alitrunk bare, except for some hairs on anterior and dorsal parts of pronotum and on propodeum. Some short appressed hairs ventrally on petiolar peduncle.

Genitalia not examined.

Type Material
Holotype worker, West Malaysia: Negeri Sembilan, Pasho Forest Reserve, in rotten wood on forest floor, 10.iii.1990, FN 27 (K. Rosciszewski), Paratypes: 2 workers with same data as holotype , 2 workers, 1 queen from same locality beneath rotten wood on forest floor, 6.iii.1990, FN 15 (K. Rosciszewski) SMNK, 1 male from same locality, colony found 31.iii.1992 in rotten wood on forest floor, bred in captivity, 23.iv.1992, FN 2430 (K. Rosciszewski) SMNK.