Polyrhachis arnoldi

Bolton (1973) - Arnold (1924:751) states that, “the only nest found was made in a shallow-concavity on the vertical trunk of a tree, the hollow being covered by a more or less circular lid, about 2 1/2 inches in diameter, made of a very closely woven silky web in which were embedded particles of bark and dirt”. In this respect the nest resembles those of Polyrhachis otleti found in secondary forest or cultivated land in West Africa.

Identification
A member of the Polyrhachis viscosa species-group. Bolton (1973) - P. arnoldi appears to be an uncommon species, related to Polyrhachis cubaensis and Polyrhachis spinicola, from which it is most easily separated by the form of the sculpturation. In related species the sculpturation is mainly of a fine reticulate-rugulation with punctate or reticulate-punctate interspaces.

Distribution based on Regional Taxon Lists
Afrotropical Region: Malawi, South Africa.

Nomenclature

 *  arnoldi. Polyrhachis (Myrma) arnoldi Forel, 1914d: 263 (w.) SOUTH AFRICA. See also: Arnold, 1924: 750; Bolton, 1973b: 324.

Worker
Bolton (1973) - TL 7.0-8.1, HL 1.74-1.89, HW 1.48-1.56, CI 82-85, SL 1.85-1.93, SI 123-125, PW 1.33-1.37, MTL 1.92-2.00. (7 measured.)

Anterior margin of the clypeus with a small median emargination. Sides of head in front of the eyes more or less straight, weakly convergent; occipital margin strongly convex. Eyes weakly convex. Alitrunk marginate throughout its length, the sides converging posteriorly so that the pronotum is notably broader than the propodeum. Pronotum bispinose; propodeum armed with a pair of short, upcurved teeth between which runs a transverse carina separating the dorsum from the declivity. The central portion of this carina is raised and appears as a prominence or blunt tooth in profile. Promesonotal suture and metanotal groove poorly developed, the former weak but distinct, the track of the latter indicated only by a break in the sculpturation. Both are transverse and are very little arched. Petiole with four spines of approximately equal length, the lateral pair somewhat more stout than the dorsal. Middle of anterior face of first gastral segment concave and accommodating the posterior face of the petiole.

Erect hairs present only on mandibles, anterior margin of clypeus and apex of gaster. All dorsal surfaces without erect hairs; pubescence developed only on the appendages. Sculpturation of clypeus a fine, superficial reticulation with scattered, very shallow pits. Head between eye and antennal insertion reticulate, rest of dorsum of head finely, longitudinally striate. Dorsum of alitrunk and first gastral segment finely and densely longitudinally striate, the second gastral segment very finely reticulate. Alitrunk laterally and anterior face of petiole finely rugulose. Colour black, dully shining; the legs usually brown-black, the palpi yellow-brown.

Type Material
Bolton (1973) - Holotype worker, SOUTH AFRICA:Natal, Durban (G. Arnold).