Eurhopalothrix heliscata

One of only a few Basicerotines that has had its biology studied. A single large colony was brought into the laboratory, observed and reported upon by Wilson and Brown (1985).

Identification
Key to Old World Basicerotini

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

Genetics
Worker prepupae from M-171 were prepared for karyotyping according to the method of Imai et al. (1977), and brain tissue was examined from four individuals, all of which gave some readable chromosome spreads. More than 60 spreads were examined at length, and nearly all of these yielded diploid counts of 18 metacentric and submetacentric chromosomes, with a few tetraploids at 36 chromosomes. As is common in such studies, a few random spreads showed chromosome totals below the usual 18 or 36, probably because one or more chromosomes had been lost from the nucleus during preparation, or were covered by another chromosome. In deducing the haploid set of 9 chromosomes, we can distinguish two large submetacentrics and a remaining series of seven, graded downwards in size to one or two metacentrics that are 1/3 to 1/2 as long as the largest members of the set, This is the first karyotype reported for any species of the myrmicine tribe Basicerotini. (Brown and Wilson 1985)

Nomenclature

 *  heliscata. Eurhopalothrix heliscata Wilson & Brown, 1985: 410, figs. 1-3 (w.q.) SINGAPORE.

Worker
Worker, holotype (Bukit Timah, Singapore): TL 4.4, HL 1.02, HW 1.12 (CI 110), ML 0.25 (MI 25), SL 0.61 (SI 54), EL 0.05, WL 1.20, petiole L 0.42, postpetiole L 0.41, hind femur L 0.76, hind tibia L 0.54 mm. [Measurements and indices as in Brown and Kempf, 1960: 167-170; L is length, W is width, I is index; cephalic index (CI) is head W (HW) X 100/head L (HL); mandibular index (CI) is mandibular L (ML) X 100/HL; scape index (SI) is scape L, measured from apex of basal lobe to apex of scape X 100/HW; EL is maximum eye L; WL is diagonal L of trunk in side view.]

Worker, composite description based on 98 specimens from the type locality and from Sungei Menyala Reserve, Malaysia, mainly compared with 'workers of Eurhopalothrix procera from 5 localities in the Philippines.

Measurements from 5 individuals in the Bukit Timah and Sungei Menyala series, including the largest and smallest of 44 checked: TL 4.0-4.7, HL 0.94-1.06, HW 1.02-1.19 (el 109-114), ML 0.23-0.29 (MI 24-27), SL 0.56-0.64 (SI 54-55), EL 0.04-0.06, WL 1.12-1.31, petiole L 0.39-0.46, postpetiole L 0.34-0.42, hind femur L 0.70-0.82, hind tibia L 0.53-0.70 mm.

1. Eyes smaller than in E. procera, deeply sunken into the dorsolateral cephalic margins, and with fewer ommatidia (estimated at 12-15 in 50 X stereomicroscope view; more than 15 ommatidia in E. procera). E. procera has EL usually > 0.06 mm.

2. Ground hairs throughout, but especially on gastric dorsum, more conspicuous, thicker, and slightly more distinctly decumbent, raised above the integumental surface. On gaster, the difference between the small ground hairs and larger, suberect specialized hairs is less pronounced than in E. procera, and the larger hairs are relatively shorter and thicker (flattened-clavate or inverted spoon-shaped), more abundant (18-26 on first gastric tergum), generally distributed, and not arranged in two longitudinal columns framing a more sparsely liveried median strip, the condition in most E. procera. Six of the larger hairs tend to form a circlet around the apical margin of the first as well as the succeeding three apical gastric segments.

3. Sculpture of body opaque in general, punctulate areas densely and coarsely so, with no shine over lower pleura. On gastric dorsum, punctulae very dense and coarse, subcontiguous, on disc of first segment, 20 or less per 0.1 mm square (more in E. procera, due to the relative fineness of the punctulae in that species), with extremely narrow interspaces which, however, are often weakly shining despite the overall opaque surface effect. Minute denticles, seen at some views on the ventral petiolar keel of E. procera from the Moluccas and eastward, are absent in E. heliscata, as in most western samples of E. procera.

4. Color deep reddish brown.

Type Material
The holotype and part of the paratype series are in the Museum of Comparative Zoology, Harvard University. Other paratypes have been placed in the British Museum (Natural History); the Australian National Insect Collection, C.S.I.R.O. (Canberra, Australia); and Cornell University Insect Collection.

Etymology
The name heliscata is taken from the diminutive of the Greek word helos, a nail or stud, and implies “mini-studded" in reference to the peculiar pilosity of the new species.