What on earth is this??

So quite some time ago, I went on vacation, yes shocker, but when I was there I had the opportunity to see some pretty awesome looking sea creatures.  Albeit it was from behind a thick bullet proof sheet of glass but still they were quite interesting to look at and one in particular makes me laugh every time, you may be able to guess which one.

 This one just gives me the creaps... I mean really, just look at it and then look at the peeping tube thing. It's just plain weird.

Ok so honestly the first one is obviously a sea horse but if someone asked me about the last three, I wouldn't have a clue.  Any ideas?