Dendronotus lacteus is a species of sea slug, a dendronotid nudibranch, a shell-less marine gastropod mollusc in the family Dendronotidae.

[2] This species was described from a specimen collected at the entrance to Strangford Lough, Northern Ireland, Irish Sea.

It was long considered to be a synonym of Dendronotus frondosus but separated by Thollesson in 2000 using the technique of allozyme electrophoresis.

[3] This was confirmed with DNA sequencing in 2015.

[4] The species is known from the Irish Sea north to Spitsbergen, Franz Josef Land, and the Barents Sea.