This species was first described by George Howes in 1911 using specimens collected at Mr O'Connors house at Tītahi Bay, Porirua and given the name Eucymatoge arenosus.

[4] In 1988 John S. Dugdale discussed this change and assigned the species to a new genus Austrocidaria.

Abdomen whitish-ochre with black bar interrupted in centre on apex of all segments.

[1][5] As well as the type locality of Titahi Bay, A. arenosa has also been recorded as occurring at Moeraki near Oamaru,[4] at Paekākāriki,[6] and near Cass.

[3] This moth is classified under the New Zealand Threat Classification system as being "At Risk, Declining".