Cadlina japonica is a species of sea slug or dorid nudibranch, a marine gastropod mollusk in the family Cadlinidae.

The slightly translucent white mantle is covered with tubercles of two sizes, larger ones separated evenly by smaller.

There are small yellow glands embedded in the mantle, clustered behind the rhinophores and towards the edges.

The rhinophores have translucent white shafts, pale brown lamellae and yellow tips.

The rhinophore pockets and gills are edged with fine yellow spots.