I was removing a few hundred pineapple sponges from my carbon media bag and left it in a bowl of RO water. This guy apparently didn’t like the rapid desalinization.
Creepy! Definitely looks like a worm and not nudibranch to me. Maybe an albino mutant bristleworm? I’m just speculating though, not an expert on worms. But I have seen a lot of nudibranch and I’m pretty sure that is not one.
Bristle worms are great CUC. I’d definitely be putting that guy back in the DT, just as a conversation piece to be like “look at my mutant bristleworm!” LOL.
Related side bar - we used to have an albino whitetail deer living in the woods near the farmland we hunt. I was pleasantly surprised nobody shot it. I like to think all the hunters in the area were just so astonished by it that we let it go. It only lived for a year or two. Natural predator likely got it. Albinism is an unfortunate mutation for a prey animal…
Definitely a bristleworm - it's unlikely it's albino, though; white bristleworm species are actually pretty common (though the white bristleworms we typically get in our tanks are tiny).