Far out. I have no idea if that's your culprit but man that is an unusual easter egg.
Here are some resources you can try:
http://seaslugforum.net/ (you can try posting your pictures there and asking for an ID, or check the species pages)
http://www.wetwebmedia.com/seaslugsopisthobranchs.htm (and/or you can email the WWM crew, they usually respond within 24 hours)
Also:
http://www.wetwebmedia.com/nudibran.htm
http://www.wetwebmedia.com/nudispt2.htm
http://www.wetwebmedia.com/nudispt3.htm
Cool find anyhow, I think.
Best of luck finding the ID, and if you do find it, please do post back here what you find out! Thanks!