I don’t know if this is plant or animal. It is attached to the coral. I have not seen this until now and on this particular night dive we saw several. I can’t find an example in any catalog yet. I got a few pictures. The first were partial images. The larger picture was fortuitous. I had just shot a fish image and noticed the subject in my LCD. So I backtracked and shot several more to come up with something sharp. They look a bit dangerous. The rule is not to touch anything, that might sting or bite. Good rule.