Unknown Hitchiker

[marcingo]

Hey. I cant get a pic of the hitchiker in question but im just wondering if anyone has any idea what this could be. It just appeared today in some live rock i bought from someone. Basically it's body is shaped sort of like a star fish. It has 5 fairly long legs and almost no body. 4 legs are at one end of the body 2 of which are longer than the other two and then 2 more legs at the other end of its body. It is appears to be striped black and white. Anyone have any ideas and if you do know what it could be is it reef safe in a 10 gallon nano?