I finally caught my little hitchhiker.

I am pretty sure it's some kind of pencil urchin from the Caribbean.
Since I read the pencil urchins can be carniverous I got him out of the main tank and into the sump.

I took a picture of him before I released him in there because he had this interesting crown of spines on top that had pincer like tips and kind of a little bulb in the middle of those spines.

I wonder what the purpose of them is? Anybody know? Justahobby post your link ;)