C. eustyla was described by Edward Meyrick in 1889 using specimen he found at Riccarton Bush in December.

[4] The lectotype specimen is held at the Natural History Museum, London.

Legs dark grey, tarsi ringed with white, middle and posterior tibiae grey-whitish.

Forewings lanceolate; snow-white; costa slenderly dark fuscous from about 1⁄4 to 3⁄4 : cilia light grey, towards base whiter, round apex wholly white or ochreous-white, with a grey dot.

[4] This species has been classified as having the "Data Deficient" conservation status under the New Zealand Threat Classification System.