Rhopalomastix impithuksai

Heterick & Kitching (2022) collected this species on tree trunks within a lowland dipterocarp forest in Brunei.

Identification
The worker of R. impithuksai is morphologically similar to Rhopalomastix javana, but can be differentiated by the following characters:
 * 1) condition of supraclypeal area – in R. impithuksai the supraclypeal area is lined with dark-pigmented longitudinal carinae with posterior apex carinate and usually acute, in R. javana the supraclypeal area does not have such carinae, with posterior apex often indistinct
 * 2) hairs on anterior face of petiole – in R. impithuksai there are few decumbent and standing hairs only present close to the apex, while in R. javana, there are standing hairs uniformly distributed on the entire anterior petiolar face
 * 3) upper half of outer face of mandible-finely striate in R. impithuksai, but smooth and shining in R. javana.

Rhopalomastix impithuksai workers may also appear similar to the morphologically variable R. johorensis, but the two species can be distinguished by the aforementioned points (2) and (3). In addition, for R. impithuksai the dorsolateral propodeal margins transition to posterior propodeal margin at bluntly rounded posterolateral corners – together with an almost flat propodeal dorsum, these give rise to a roundly obtuse posterior propodeal junction. In contrast, for R. johorensis, the combination of ill-defined posterolateral corners of the propodeum and a gently downward-sloping propodeal dorsum, give rise to an indistinct though broadly-rounded propodeal junction.

The large worker of R. impithuksai is also morphologically similar to smaller workers of R. robusta, but may be differentiated based on characters described in more detail under Rhopalomastix robusta.

Brunei
Heterick & Kitching (2022) - Indomalay Rhopalomastix spp. are tiny (< 2mm) and identification using the key in Wang, Yong & Jaitrong (2021) depends on interpreting subtle features of the mandible (fine striae present or absent) and the appearance of the posterolateral propodeal angles. The single Brunei minor worker keys out to R. impithuksai with a little awkwardness owing to the extremely subtle characters needed to make a determination. Rhopalomastix impithuksai is known from a single colony collected in Thailand and species can be localised, so the Brunei taxon may represent a different but closely related member of this group.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Brunei Darussalam. Oriental Region: Thailand.

Nomenclature

 * . Rhopalomastix impithuksai Wang & Jaitrong, in Wang et al., 2021: 123, figs. 2a, 3, 4, 16a (w.m.) THAILAND.