Sea Worm

Found this stranded on the beach. Picked it up to put it back into the sea and it split into many pieces and squirt this teal fluid about 2'. All of the pieces were squirming. I left it alone. The head was shaped like a snake kind of but flat. It had hundreds of swimming legs. It's length was at least 2'. Flat on the bottom rounder on the top. I thought it was an eel, that's why I picked it up to help it back into the water. It was SCAREY!