It's definitely a nudibranch and looks unusual to me (although I am not a nudibranch expert!). I suggest you contact Terry Gosline or members of his lab at the Cal Academy - they may be interested.
Sorry - I mistyped his name - he's got an "r" at the end of his last name (Gosliner). He's one of the curators and scientists, and he specializes in nudibranchs. Lots of info here: http://www.zoominfo.com/people/Gosliner_Terry_4498628.aspx