Pronotum globose with rounded sides and large deep puncta; overall a dark blackish purple with varying amounts of violet, blue or green; has white powdery material ('mealiness'), mainly within puncta on head, pronotum and ventral side. Elytra with many relatively shallow, closely spaced ribs and shallowly scalloped apices that are weakly spinose or bispinose.

Two specimens of this species were collected on Kangaroo Island in 1878 by Waterhouse, as noted by Matthews 1985. Apart from this the species was only known in SA from old collections without specific localities, and a dead salt lake specimen, until the discovery of its larval host plants by Lang & Stolarski 2020. The host plant species are generally uncommon and patchily distributed which is probably a contributing factor to the species' rarity.

Various life stages of M. globithorax have been found at diverse locations in live stems of three shrub species of family Santalaceae: Choretrum chrysanthum, C. glomeratum and Leptomeria aphylla. Continuity of frass-filled tunnels indicates that larvae feed downwards, starting from small upper branchlets as narrow as c. 2 mm diameter to eventually pupate in the trunk or main stems near the plant base, and this is supported by observations of ovipositing behaviour (Lang & Stolarski 2020).

In WA, adults have been mostly attracted to yellow lures (T.M.S. Hanlon & M. Powell 2020, pers. comm), as is the case in SA. This accords with the foliage colour of the Sour-bushes that are its main larval host plant species: in Choretrum chrysanthum it is greenish yellow or golden yellow, and in C. glomeratum it is pale and whitish but often tinged with greenish yellow.