octopus?

[Aquattro]

yes, you can buy them. Yes, you can keep them, the method depends on the octopus. Most only live a year or two, they will escape from your tank, and they will likely eat anything you put in the tank. Oh, they hide most of the time. And escape a lot. Some can kill you, others need temparate water. And they escape a lot. But, ya, it can be done.

I used to keep one in the biology department at school. I used to have to retrieve it all the time from the hallways! Did I mention that they escape a lot?