Dumbo octopuses belong to the family of octopuses called Opisthoteuthidae which are also known as umbrella octopuses. They are called such because they have webbing between their arms and so when they spread their arms out, they look like umbrellas when viewed from the bottom. One of them even looks so flat and round that it is called the flapjack or pancake octopus.
Another characteristic umbrella octopuses have is that they only have suckers on their tentacles, unlike some octopuses which also have spines on their tentacles with which to defend themselves against predators.