Hypselodoris nigrolineata is a species of colourful sea slug or dorid nudibranch, a marine gastropod mollusk in the family Chromodorididae.

[2][3] This nudibranch is found in the Indian Ocean off Kenya and Tanzania.

[4][5] Hypselodoris nigrolineata has a white-cream body and a bright purple mantle edge and foot.

There are often black striated lines running longitudinally along its dorsum.

[6] This species can reach a total length of at least 35 mm.