Hypselodoris iba has previously been confused with Hypselodoris bullocki although DNA sequencingsuggests that it is a mimic rather than a close relative. It has a range of colour forms. Typically it has a violet semi-translucent body with a bright opaque white margin to the mantle. The violet colouration can be absent and replaced by milky white or present just as a more intense innerborder to the mantle. In these pale colour forms there is usually a brown patch in the middle of the back, edged with violet. The gills are pale at the base becomingorange or brown towards the tips. The rhinophores have orange or brown clubs and usually have purple bases. A characteristic which distinguishes this species from similar coloured species in the Hypselodoris bullockiclade is that the mantle behind the gills is quite abruptly narrowed and contain a concentration of subcutaneous defensive glands. This species can reach a total length of at least 70 mm.