Pteraeolidia ianthina is a sea slug, an aeolid nudibranch in the family Facelinidae.

[8] It is one of the most common aeolid nudibranchs found in Eastern Australia and can inflict a painful sting to humans.

The slug is elongated (7 cm (2.8 in)) with many clusters of medium-large sized cerata along the length of the body.

The fat rhinophores and the long cephalic tentacles have at least two dark purple bands that stand out.

Algal zooxanthellae of the genus Symbiodinium derived from the food of these animals continue to photosynthesise inside the body and give rise to brown and green pigments.