The length of the body varies between 7 mm and 25 mm. In this species the mantle can vary in color from reddish purple to pinkish orange. The mantleborder is creamy white. Just inside the mantle border are a series of reddish purple streaks or smudged marks which are a more vibrant purple than the main body color. Along the midline of the animal is a white patch that matches the white border. This patch sometimes encircles the gills and extends anteriorly between the rhinophores. The line is often broken into two patches anterior-posteriorly. The rhinophores and branchia have an orange-red tint. Identifying individual purple sea slugs within the genus Noumea can be challenging because .
Ecology
The food source for this species has not been definitely identified, however this species has been found on corallinealga, which may prove to be part of its diet.