Reddish copper colouration, much overlain by dense white mealiness, especially on the ventral side. Pronotum mostly with coarse puncturation, but a zone of denser and finer puncta medially in the anterior. Compared to M. scintillans, the lateral margins of the pronotum are more strongly contracted towards the anterior and posterior (but less so than in M. globithorax), and the elytra are more strongly tapered apically, and have much smaller puncta and more clearly defined costae which are scarcely punctate.
Distinguished from M. globithorax by the elytra having tridentate apices and intercostal areas which are densely and finely punctate and much wider than the costae (ribs).
Differs from Notobubastes costata in the broader body shape, more rounded pronotum with a longer and more pronounced median sulcus, and areas of coarser puncta and sculpturing on the pronotum and elytra.

The first SA record of this species was collected as a live adult from NW of Port Augusta by Mark A. Hura in December 2008.

I treat it here as an undescribed species of Microcastalia, although it might as easily fit Notobubastes, a genus considered by Bellamy & Peterson 2000 to be closely related and 'perhaps the sister group' to Microcastalia. Their maintenance as two separate genera warrants investigation. Microcastalia is the older name and would have priority.

This species has the same white powdery excrescence in the puncta and other declivities as found on M. globithorax when fresh.

Initially, the first specimen (MAH 04165) was mistakenly included in M. scintillans (q.v.) by (Lang & Stolarski 2020), and also on this website until June 2023. Mark (T.M.S.) Hanlon, however, pointed out that it was a different taxon which was known to occur in WA.

On 30 December 2024 three more specimens were collected from north of the Flinders Ranges by A.M.P. Stolarski.

The first SA specimen was found sitting on a branch of a young Western Myall (Acacia papyrocarpa), and its pristine condition suggested that might be the host from which it had only recently emerged. However, in WA the species is known to be associated with stems and branchlets of Hop-bush (Dodonaea) species (M. Powell; M. Hanlon, pers. comm. 2020). I visited the collection site of MAH 04165 and found an isolated stand of several bushes of Dodonaea viscosa ssp. angustissima c. 150 m away, including one bush with a suitably sized frass-filled tunnel and exit hole.

The three specimens from north of the Flinders Ranges were collected from Narrow-leaf Hop-bush D. viscosa ssp. angustissima by A.M.P. Stolarski, two by sweeping foliage and the third as a dead spider web specimen.