[2] This species was described from Nanoose Bay, Regional District of Nanaimo, Vancouver Island, British Columbia, Canada.

Orienthella trilineata is a seasonally abundant aeolid ranging from Baja California, Mexico to Alaska.

Orienthella trilineata is a flabellinid nudibranch with a translucent body and three longitudinal white lines on the back and sides.

The line down the middle of the back passes between the rhinophores where it splits and continues to the tips of the oral tentacles.

The rhinophores are perfoliate and coloured white at the base but orange in the outer third.