Ondina dilucida is a species of sea snail, a marine gastropod mollusk in the family Pyramidellidae, the pyrams and their allies.

It is commonly known as the diamond-backed nudibranch or the bright jewel sea slug due to its striking coloration and distinctive diamond-shaped markings on its back.. Ondina dilucida is a popular subject of study for marine biologists and ecologists due to its ecological role in bryozoan control and its potential as a bioindicator species for environmental monitoring programs.

Additionally, its striking coloration and interesting behavior make it a favorite among underwater photographers and nature enthusiasts.

This species occurs in the following locations at depths between 125 mm and 500 m:[1]

This Pyramidellidae-related article is a stub.