I'm pretty sure this is Favorinus sp.
There are several places that describe it as Favorinus sp. 2
(even though this page says sp.1, he identifies it earlier as sp.2). The "Nudibranch & Sea Slug ID Indo Pacific" book describes sp.2 as -
15mm, Orange Red with orange lines on the oral tentacles; cerrata brown with conspicuous lamellae and black apices; cerata orange with white subapical rings and purple tips....
- cjames likes this