On their supporting disc to Moths of Victoria (Part 2) they recognise two distinct un-named species other than P, bicosta., 'Paleaosia sp.(1)' and 'Paleaosia sp.(2)'. Palaeosia sp.(1) has a fine, yellow edge on a pale costa, Grey collar, cream head, dark forewings., wingspan usually greater than 30 mm. Paleaosia sp.(2) has a pale costa, black edge at the base grading to yellow, Pale collar and head, pale forewings. wingspan variable, less than 40mm.
Moths of Victoria show both sexes of P. bicosta having a distinct costa with strongly contrasting red-orange and cream streaks.