Okenia mija is a species of sea slug, specifically a dorid nudibranch, a marine gastropod mollusc in the family Goniodorididae.

[2] This Okenia has a narrow body and seven pairs of short lateral papillae.

There are many papillae on the back, between the rhinophores and the gills and some on the sides of the body.

The body is translucent and has some small spots of brown and white pigment.

The diet of this species is a bryozoan, Amathia wilsoni.