Eurhopalothrix isabellae

Identification
The mandibular form and dentition immediately distinguish this peculiar species. The mesosomal sculpturation is heavier than that of any known Eurhopalothrix procera variant, and the vestiture is less strongly developed. (Taylor 1968)

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

Nomenclature

 *  isabellae. Rhopalothrix isabellae Mann, 1919: 357, fig. 35 (w.) SOLOMON IS. Combination in Eurhopalothrix: Brown & Kempf, 1960: 225. See also: Taylor, 1968b: 344.

Worker
Worker. Length 3 mm.

Head about as long as broad; strongly excavated behind and with obtusely angulate corners ; oblique portions of sides with straight margin. Clypeus narrowed behind and broadly and shallowly concave in front; the suture separating it from the front shallow and rather poorly defined. Mandibles strongly constricted at basal third and much more slender than in the related species. Antennal scapes at base about a third as broad as long; funicular joints two and three only slightly transverse, joints three and four longer than broad, terminal joint longer than the four preceding joints together. Pronotum shallowly impressed at middle and obtusely gibbous on either side; humeral angles rounded, without any indi:!ation of tubercles. Promesonotal suture obsolete. Mesonotum slightly convex in front, and depressed behind. Mesoepinotal suture distinct. Base of epinotum strongly impressed mesally, marginate at sides of impression, separated from the concave declivous portion by an acute margin; spines short and obtuse apically, their bases extended as narrow lamellae along borders of declivity. Petiolar node longer than broad, slightly broadest apically and very feebly convex at sides and front; flat above; about as long as peduncle. Postpetiole one and a third times broader than long, narrowed in front, sides little convex; dorsal surface with a faint medial impression which terminates in front in a broad and shallow fovea; strongly impressed at apex and elevated into an obtuse tubercle on either side of impression. First gastric segment indistinctly impressed at middle of base.

Mandibles shining and punctate. Head feebly shining. Clypeus strongly and foveolately punctate; front reticulately and rugosely punctate; vertex with two large shallow foveae and cribriform punctures between. Promesothorax coarsely and reticulately costate and subopaque. Epinotum at sides more finely costate; impressed portion foveolately punctate; declivity smooth and shining. Petiole finely rugose. Postpetiole and gaster more shining and uniformly cribrate. Antennae and legs coarsely and densely subopaque.

Fine, squamiform hairs on head and antennal scapes, coarse ones on legs. Clavate hairs on legs, outer border of scape and one in each of the two foveae on vertex; fine hairs on funiculus, tarsi, and ventral surface of gaster.

Fuscopiceous; legs, mandibles, antennae, and lamellate borders of epinotum fuscorufous. Hair white.

Taylor (1968) - Holotype worker. Dimensions: HL, 0.85; HW, 0.89; CI, 105; SL, 0.55; SI, 62; greatest diameter of eye, 0.06; PW, 0.52; WL, 1.07; petiolar node width, 0.26. The following notes supplement Mann's original description:

(1) Basal mandibular tooth a broad, low, blade-like structure, about twice as wide at base as the acutely triangular succeeding teeth.

(2) Dorsum of petiolar node distinctly longer than broad, its midline length almost 1.2 times the maximum width.

(3) Head feebly shining, with somewhat effaced medium punctate-rugosity. Mes- and metepisternites, posterolateral parts of propodeum, and lateral areas of petiolar peduncle shining, moderately finely punctate. Propodeal declivity smooth and shining, divided transversely by a fine carina. Gastric sclerites moderately shining, almost entirely cribrately punctate (punctural diameters and interpunctural distances averaging about 0.01 mm).

Additional worker material. These specimens have the following dimensions: TL, c. 2.9-3.5; HL, 0.69-0.82; HW, 0.72-0.86; CI, 104-105; ML, 0.20-0.23; MI, 28-29; SL, 0.41-0.50; SI, 57-60; greatest diameter of eye 0.06-0.08; PW, 0.42-0.49; WL, 0.78-0.95; petiolar node width, 0.20-0.22; postpetiole width, 0.45-0.51; gastric width, 0•29-0' 34. They differ from the holotype as follows:

(1) Smaller size.

(2) Mandibles less narrowed anteriorly and thus more distinctly triangular, with outer borders less concave and posterior borders slightly less oblique, so that the triangular gap between the closed jaws and the clypeus is less extensive.

(3) Occipital border slightly less deeply emarginate in frontal view.

(4) Metanotal groove less distinctly impressed on mesosomal dorsum.

(5) Petiolar dorsum at most only minutely longer than broad.

(6) Median longitudinal depression of postpetiole less pronounced.

(7) Head less distinctly sculptured, obscure and finely punctate-rugose, the overall effect perhaps best described as coarsely shagreened. Mes- and metepisternites, posterolateral parts of propodeum, and sides of petiolar peduncle smooth, but less strongly shining than in holotype, due to an overall minutely granular micro-sculpture, which has a slight metallic lustre in some lights. Propodeal declivity divided into upper and lower portions by a sharp transverse carina; lower portion impunctate, smooth and shining; upper portion sub opaque, with scattered fine punctures and with 4 or 5 vague transverse rugae, best seen in crosslight. First gastric tergite moderately shining, with vestigial traces of effaced coarse puncturation, most distinct at edges. Sternite coarsely punctate, as in holotype.

(8) Cephalic ground pilosity as in Eurhopalothrix greensladei, essentially lacking on frons except for outer edges of occipital lobes. Dorsa of petiole and postpetiole with distinct, scattered, whitish hairs, about 0.02 mm long. (The hairs in these positions are much less distinct on the holotype, which has them distinctly developed on the frons, unlike the Vella Lavella specimens). Enlarged erect hairs restricted to a single verticoccipital pair, and those at gastric apex, as in the holotype.

(9) Colour as in E. greensladei, somewhat darker than the holotype is currently; judging from Mann's description the latter has probably faded.

Type Material
Ysabel: Fulakora. The single worker of this anomalous species was found beneath a log in the forest.