What type of nudibranch is this?

[biocuber]

About a week ago I noticed what looked like a baby nudibranch in my frag tank, by the time I got my camera it had disappeared. Today 3 more of these little guys showed up and I was able to get some photos this time. They are around 1/4" long and I am pretty sure that they are a nudibranch of some type. If anyone knows what species they might be I'd love to hear so that I can find more info on them.