They are lettuce nudi's. I have read that sometimes they will chew on byropsis, but that seemed like a few and far between statement. I did discover where my byropsis was hiding. It took root against the back wall between the wall and a powerhead. Cleaned that up. I'm sure it is still around, but it is in check. If I end up seeing one chew on some byropsis I'll let you know. Is your outbreak bad or are you just paranoid about it?
Also, I caught the rogue nudibranch last night. I relocated him in the 36 FOWLR
tank with the eel and flame angel. It has adjusted and doing its thing and I will continue to watch it. I've never seen a nudi like it. Rather than it having the riffled ridges along its back...it is more like a skirt the whole way around it. Pretty cool. Reminds me of an egg after you crack it...just with a black skirt and white center. I'm debating what it was eating...it can't be new to my tank as nothing new has been added that could have carried something that large in quite some time. I'm thinking it was in one of the mud spots in some of the LR
that I couldn't get cleaned out.