Called a Remora, they have sucker on the top head and attached to sharks, stingray etc. Free ride and eat all the left overs too.

While diving in Palau, a lonely remora was following us, one of the divers thought it would be funny to grab it and stuck it to his bare stomach. He found out pretty quickly that it’s not suction that holds them on, but rather many rows of barbs! Boy, you should have seen his eyes tearing that thing loose from his skin! The joke was definitely on him!