an octopus is not a devilfish

Octopus is commonly known as the devil fish. There is no species of that name "Devilfish Octopus". But octopuses have a large variety in sizes as well in species. here is a website with a list of species and their sizes.

No, the devilfish in "Island of the Blue Dolphins" is not an octopus. It refers to a large manta ray that the main character encounters and hunts in the book.

Yes, they are just like octopus with long arms.

it has eight arms stupid it a octupus