Key to Old World Basicerotini

This worker key is based on Taylor, R. W. 1990. New Asian ants of the tribe Basicerotini, with an on-line computer interactive key to the twenty-six known Indo-Australian species (Hymenoptera: Formicidae: Myrmicinae). Invertebrate Taxonomy. 4:397-425.

The known queens of Asian Eurhopalothrix species run through the key consistently with their workers. They represent Eurhopalothrix dubia, Eurhopalothrix heliscata, Eurhopalothrix jennya, Eurhopalothrix omnivaga and Eurhopalothrix procera.

1

 * Mandibles linear, their insertions remote, so that the masticatory borders cross or engage only near their apices (genus Rhopalothrix) . . . . . 2


 * Mandibles triangular, their whole serially dentate masticatory borders engaging directly at full closure (genus Eurhopalothrix) . . . . . 3

2
return to couplet #1
 * Specialised large hairs on cephalic dorsum numbering 16, with 8 in anterior row (supernumerary hairs may occur; Taylor 1970); hairs on disc of first gastral tergite of one size class; mesosomal dorsum with a distinct transverse metanotal impression, the propodeal dorsum a transverse tumosity behind it; propodeal teeth well developed, forming angles of about 90° in side view (E. Australia-S.E. Queensland, N.E. New South Wales) . . . . . Rhopalothrix orbis


 * 18 specialised hairs on cephalic dorsum, with 10 in anterior row; hairs of first gastral tergite of 2 size classes; metanotal impression feeble; propodeal dorsum sloping back abruptly towards declivity; propodeal teeth only obtuse vestiges (N.E. New Guinea) . . . . . Rhopalothrix diadema

3
return to couplet #1
 * S.E. Asian and Philippines species found to the west of New Guinea . . . . . 4


 * Melanesian, Australian and Pacific species . . . . . 15

4
return to couplet #3
 * Sides of mesosoma behind pronotum smooth and shining, essentially unsculptured (widespread in Indo-Pacific area) . . . . . Eurhopalothrix procera


 * Sides of mesosoma behind pronotum dull, distinctly sculptured, usually with large shallow pit-like 'thimble punctures' separated by about 0.5-1 x their average diameter; alternatively (in 1 Philippines species) these surfaces are densely and moderately coarsely punctate-shagreened . . . . . 5

5
return to couplet #4
 * Punctures of frons and most dorsal body surfaces each filled by a flat-surfaced, feather-edged, metallic silvery hair; this exceptional ground pilosity often largely contiguous, especially on the frons; eyes relatively large, with about 16-20 facets, maximum diameter close to that of a funicular club (E. platisquama group) . . . . . 6


 * Hairs of ground pilosity not as above, usually very reduced, sparse, or both, never squamous or silvery-metallic; eyes either absent or much smaller, usually with fewer than 10 facets . . . . . 8

6
return to couplet #5
 * Four erect, narrowly clavate hairs, separated by about their average length, clustered in a square array on the frons, at the midline near the occipital border. (Other similar hairs may be present elsewhere on the head) . . . . . 7


 * A single pair of laterally adjacent hairs in the position described, with another hair close to the occipital border on each side, about midway between the median pair and the posterior occipital angle (Sarawak) . . . . . Eurhopalothrix seguensis

7
return to couplet #6
 * Frons with a single erect hair on each side about mid-way between the posteromedian cluster and the ipsilateral eye (Sabah) . . . . . Eurhopalothrix dubia


 * Frons lacking erect hairs apart from those of the posteromedian cluster (W. Malaysia, Sumatra) . . . . . Eurhopalothrix platisquama

8
return to couplet #5
 * Frons with 6 or more erect, clavate, or ornately specialised large hairs . . . . . 9


 * Frons with only a single pair of large erect, simple, clavate hairs, situated on its posteromedian sector . . . . . 10

9
return to couplet #8
 * Enlarged hairs of frons globular, prominent and strikingly creamy-white; 16 in number in 3 transverse rows; the anterior, transocular, row with 8 hairs, the others each with 4; ground pilosity of first gastral tergite prominent, its hairs virtual miniature versions of the enlarged globular hairs which accompany them (Sarawak, Sabah, Sumatra) . . . . . Eurhopalothrix coronata


 * Enlarged cephalic hairs erect, slender, only slightly clavate and relatively inconspicuous, golden-brown in colour; 6 in number, 4 apparently the remnants of a transocular row, and 2 behind them placed near the median occipital border. Ground pilosity of gaster fine and inconspicuous (Sarawak) . . . . . Eurhopalothrix jennya

10
return to couplet #8
 * Posterior occipital angles obsolete, occipital border broadly arched between the lateral occipital angles, which form the lateral extremities of the cranium (Philippines) . . . . . Eurhopalothrix philippina


 * Posterior occipital angles well developed, though sometimes very obtuse, the occipital border between them broadly concave . . . . . 11

11
return to couplet #10
 * Larger species (HW across lateral occipital angles> 1.0 mm) (E. heliscata group) . . . . . 12


 * Smaller species (HW<0.78 mm) . . . . . 13

12
return to couplet #11
 * Petiolar node in dorsal view distinctly longer than broad; a relatively coarsely sculptured species with prominent ground pilosity on frons, promesonotal dorsum, petiole and postpetiole; pro- and mesonotal sections of promesonotum separated by a more-or-less distinct transverse trough (W. Malaysia) . . . . . Eurhopalothrix heliscata


 * Petiolar node in dorsal view approximately square, its length and breadth subequal; overall less heavily sculptured, with scattered, diffuse, sparse ground pilosity of small fine hairs, not concentrated as described above (Luzon, Philippines) . . . . . Eurhopalothrix chapmani

13
return to couplet #11
 * Outer borders of mandibles distinctly concave, basal borders oblique, framing a n arrowly transverse triangular gap against the anterior clypeal border when the jaws are closed; larger species (HW>0.63 mm) (widespread: Perak to Sumatra, Sarawak, Sabah and Sulawesi) . . . . . Eurhopalothrix omnivaga


 * Outer borders of mandibles more-or-less evenly convex; posterior borders closing tightly against clypeus, without an intervening gap; smaller species (HW < 0.59 mm) (northern Borneo) . . . . . 14

14
return to couplet #13
 * Petiolar node distinctly longer than wide in dorsal view (Sabah) . . . . . Eurhopalothrix browni


 * Petiolar node distinctly transverse in dorsal view (Sarawak) . . . . . Eurhopalothrix rothschildi

15
return to couplet #3
 * Mandibles with a broad, low basal tooth, approximately twice as wide at base as the succeeding teeth; erect clavate hairs (except those on gastral apex) restricted to a single pair on verticocciput; HW 0.72-0.89 mm . . . . . 16


 * Mandibular teeth conical, subsequal in size throughout; erect clavate hairs usually not distributed as above; size frequently different . . . . . 17

16
return to couplet #15
 * Propodeal teeth well developed, supporting broad infra-dental lamellae, a triangular area of propodeal dorsum anterior to their bases distinctly concave and more-or-less clearly set off from the remaining dorsum; colour medium-dark reddish brown (Solomon Is., Ysabel and Vella Lavella) . . . . . Eurhopalothrix isabellae


 * Propodeal teeth vestigial, surmounting very narrow infra-dental lamellae; propodeal dorsum almost entirely convex, with at most only slight traces of a posteromedian concavity; colour bright golden chestnut-brown (Manus Island) . . . . . Eurhopalothrix cinnamea

17
return to couplet #15
 * Smaller species, HW < 0.75 mm . . . . . 18


 * Larger species, HW>0.93 mm . . . . . 22

18
return to couplet #17
 * Posterior third of head covered thickly with conspicuous, white, orbicular squamiform hairs (including the specialised hairs, which are only weakly differentiated in this species); pilosity of anterior two-thirds of head abruptly reduced to fine, minute vestiges, this area appearing naked by contrast (N.E. New Guinea) . . . . . Eurhopalothrix biroi


 * Pilosity of head otherwise; either reduced throughout or without an abrupt difference between anterior and posterior sections; specialised larger hairs, when present on dorsum of head, strongly differentiated and more-or-less clavate . . . . . 19

19
return to couplet #18
 * Specialised erect hairs of head absent (N.E. New Guinea) . . . . . Eurhopalothrix punctata


 * Specialised erect hairs of head, when complement is complete, numbering 16-18, arranged in 3 transverse rows . . . . . 20

20
return to couplet #19
 * Larger species (WL>0'65 mm); dorsal face of propodeum with an angular impression or ‘step’ at its midlength (New Caledonia) . . . . . Eurhopalothrix caledonica


 * Smaller species (WL < 0.65 mm); dorsal face of propodeum forming an evenly concave slope . . . . . 21