Myrmoteras mcarthuri

Individuals of the type series were collected from the under and between stones along a the banks of the Calbiga-a River.

Identification
Zettel & Sorger (2011) - Colour mainly medium brown. Dorsum of head densely granulate and dull. Median frontal sulcus anteriorly obliterate, posteriorly deep. Gap between clypeus and frons narrow. Posterior face of temples (behind ridge) finely granulate. Labrum not strongly projecting, without long trigger hairs. Mandible with apical part not bent ventrad, with two minute preapical denticles; Mandible Index 145–154. Funiculus of antenna slender, antennomere 3 ca. twice as long as broad and hardly shorter than antennomere 2. Disk of pronotum densely granulate and dull. Mesonotum strongly depressed. Dorsum of propodeum strongly convex. Middle tibia weakly dilated, more than 5 times as long as wide. Petiolar node wide in lateral aspect.

Myrmoteras mcarthuri is similar to Myrmoteras williamsi and has been initially mistaken for this species by the first author. However, close examination of material from Leyte yielded the discovery that in fact it represents a distinct new species. Myrmoteras williamsi was described based on sexuals (two gynes and one male) from Los Baños, Laguna, Luzon Island (Wheeler 1919). Moffett (1985) redescribed gynes (types and additional specimens) from Luzon and Negros and workers from Dumaguete, Negros Island. Although he noted important differences between the material from the two islands, he considered them as conspecific, following Creighton (1930).

Myrmoteras williamsi gynes collected at the type locality and deposited in the first author’s collection agree perfectly with the original description of this taxon. Myrmoteras mcarthuri differs in some important characteristics from M. williamsi: In M. mcarthuri the posterior face of the temples, behind a blunt ridge, is granulate, where it is smooth and shiny in M. williamsi. The Mandible Index is larger in M. mcarthuri (145–154) than in M. williamsi (124–130; measurements partly from Moffett 1985). In lateral aspect, the petiolar node is wide in M. mcarthuri, but narrow in M. williamsi. Another very obvious difference is found in the antenna: The funiculus of M. williamsi is stouter than that of M. mcarthuri, especially the basal joints (except antennomere 2) are not much longer than broad in M. williamsi, while their length is almost twice their width in M. mcarthuri. The length of antennomere 3 is approximately 0.7 times the length of antennomere 2 in M. williamsi, but almost 1.0 times in M. mcarthuri. In addition, the length of setae, especially on pronotum, is slightly longer in M. mcarthuri than in M. williamsi.

Although this compares a gyne with a worker, all characters mentioned do not seem to be morph-related, at least there are no differences in the differential diagnoses of worker and gynes of other species (see Moffett 1985).

Myrmoteras mcarthuri differs from Moffett’s (1985) description of “M. williamsi” workers from Negros, as the latter “have a feeble granulate sculpture on the legs, scapes, and mandibles” which is absent in M. mcarthuri. We suspect that this Negros material will turn out being another undescribed species.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Philippines.

Nomenclature

 *  mcarthuri. Myrmoteras (Myagroteras) mcarthuri Zettel & Sorger, 2011: 65, figs. 7-10, 13 (w.) PHILIPPINES (Leyte I.).

Worker
Holotype. TL 5.21, HW 0.97, HL 0.96, EL 0.58, ML 1.49, MI 154, SL 1.12, SI 115, PW 0.64, WL 1.46.

Paratype. Range of 10 workers: TL 4.93–5.27, HW 0.92–1.01, MI 145–152, WL 1.38–1.52. Measurements of worker with smallest HW: TL 4.94, HL 0.95, EL 0.56, ML 1.40, MI 147, SL 1.06, SI 115, PW 0.60, WL 1.38. Measurements of worker with largest HW: TL 5.27, HL 1.00, EL 0.60, ML 1.48, MI 148, SL 1.17, SI 116, PW 0.65, WL 1.50.

Colour: Medium brown, gaster slightly lighter than head and mesosoma, propodeum weakly infuscated in some specimens. Mandibles and antennae brownish yellow. Palpi yellow. Legs medium brown except tarsi brownish yellow.

Structures: Head with moderately dense pilosity, longest hairs ca. 0.13 mm long. Frons, temples densely granulate and dull (but granulation obsolete at ventroposterior part of temples). At anterior of frons granulation more or less confluent to longitudinal rugae; median frontal sulcus narrow, posteriorly deeply impressed and reaching anterior ocellus, anteriorly not reaching frons margin. Antennal scrobes small, shiny, anteromedially limited by short, curved rugae. Temple with sharp ridge separating a concave anterior from flat posterior. Clypeus with slender medial elevation, with some faint longitudinal rugae, mostly near margins; anterior margin deeply concave. Mandibles very long, smooth, dentition. Maxillary palp with 6, labial palp with 4 segments. Antenna with slender funiculus, each segment about twice as long as broad (except long ultimate), antennomere 3 hardly shorter than antennomere 2 (in holotype, measured at leading edge, 0.96 times).

Mesosoma, node and gaster with relatively dense pilosity, longest hairs ca. 0.13 mm long: Pronotum low and evenly convex, summit at level with anterior of mesonotum. Mesonotum and propodeum with granulation overlaid by some irregular rugae. Pair of distinct ridges extending from metanotal tubercle forward are present. Metanotal groove visible as impressed notch in lateral aspect. Meso- and metapleura with longitudinal striation, partly some granulation visible in addition. Middle and hind tibiae moderately dilated, middle tibia of holotype 5.4 times as long as wide. Foretibia slender. Node of petiole thickened in lateral aspect. Gaster smooth.

Type Material
Holotype (worker) from the Philippines, Leyte Island, Baybay, at lower slopes of Mt. Pangasugan, on ground under and between stones at banks of Calbiga-a River near Leyte State University, ca. 50–100 m a.s.l., 20–21 March 2005, leg. H. Zettel & C. V. Pangantihon (# 422).

Paratypes: 7 workers from the same nest as the holotype. 3 workers from the Philippines, Leyte Island, Baybay, Lago-Lago River near Leyte State University, ca. 50 m a.s.l., 19 March 2005, leg. H. Zettel & C. V. Pangantihon (# 421).

Holotypes are deposited in the Entomological Collection of the University of San Carlos, Cebu City, paratypes in the Natural History Museum Vienna and in the authors’ reference collections.

Etymology
We name this species in honour of our friend and most enthusiastic myrmecologist Archie McArthur from the South Australia Museum. Coincidally, the type locality is on the island where General Douglas MacArthur (1880–1964) landed in 1944 to end the Japanese occupation of the Philippines.

References based on Global Ant Biodiversity Informatics

 * Zettel, H. & D.M. Sorger. 2011. New Myrmoteras ants (Hymenoptera: Formicidae) from the Southeastern Philippines. Raffles Bulletin of Zoology 59(1):61-67