Goniodoris castanea is a species of sea slug, a dorid nudibranch, a marine gastropod mollusc in the family Goniodorididae.

It has subsequently been reported widely in Britain and Ireland and from Norway to the Mediterranean Sea.

[4][5] This goniodorid nudibranch is variable in colour, usually red-brown or dark purple but also bright red.

Most individuals have scattered irregular small patches of white or grey all over the body.

[7] Goniodoris castanea feeds on tunicates of the genera Botryllus and Botrylloides, family Botryllidae.