Remora

The Remora, or Suckerfish, has an oval disc on top of their head that creates suction. It can attach itself to large marine animals to get a free ride and feeds on leftovers from the host. It can also attach itself to divers.

I once had company of a Remora that stayed 10 cm under my chest for a long period. 

The Remora can be up to 60 cm in length.