The octopus is considered the most intelligent invertebrate there is. They also appear to have a good memory. Tales abound of their achievements in aquariums. The Internet is full of videos showing their tricks.
~In 1994, an octopus named Octavia drained her tank when she pulled a plastic pipe loose at her aquarium. 200 gallons of seawater flooded various displays and also offices. Employees entering the Santa Monica Aquarium Thursday morning were greeted by seawater and a lazy, tiny octopus floating in a nearby tank that was nearly empty of water. She stared at them as they cleaned up the mess.
The aquarium education specialist estimated the water flowed for 10 hours before anyone found it. She had swum to the top of her enclosure and disassembled a water control valve. This caused a spray of water outside of the tank and flooded the aquarium with 2 inches of water.
By watching the video, it becomes apparent that an octopus is easily trained.