I had the same one in the pic, Hawaiian Bobtail Squids, Euprymna scolopes. I knew they werent cuttle fish. I just said it sorta resembles them. They are pretty easy to keep but sensitive to ph fluctuations and copper is a killer. THey eat ghost shrimps regularly.
Maybe you can keep one of these guys in your 3 gallon. They get no bigger than 1 inch. Not an octo but looks like a cross between a squid and an octo. Almost looks like a cuttle fish. Bad news as with almost all cephs, they have a short life span, about 8 months.
Hawaiian Bobtail Squids...