What in the world is this?

[noirsphynx]

Nudi's are soft this guy is rough textured. It honestly looks just like a piece of live rock, kinda feels that way too. I would have never known it was there if it had of remained on the rocks. From what I'm seeing on the net the only thing I can find somewhat similar looking is a cucumber but I think they're round and stay on the substrate......right? Maybe it is a sea hare?