You know fun fact I learned recently from a let's play: tentacles only refer to the appendages which end in suckers, but along the rest of their length, have no suckers. The other appendages are called arms. So, octopuses actually have no tentacles, they have arms. Squids have 8 arms, and 2 extra tentacles, which are the long ones that have little spade shaped sucker hands on them. So, probably when you pictured tentacles, you were actually picturing cephalopod arms.