Thorunna is a genus of sea slugs, dorid nudibranchs, shell-less marine gastropod mollusks in the family Chromodorididae.

[3][4][5] The genus Thorunna contains chromodorid nudibranchs with a distinctive radula, which is very small and has 17-25 teeth in a half-row.

The lateral teeth are long slender shafts with bluntly bifid tips.

Species in this genus rarely exceed 20 mm (0.79 in) and wriggle or vibrate their gills rhythmically.

Anatomically the buccal bulb is very small relative to most chromodorids and the oral tube very long.