Fiddler Crabs!
They sell them at Wal-Mart, they are an adorable example of “what if Hellboy was a pokemon”, and they are seriously so cute, I wish I had more space and money and time so I could replace a whole window with a fish tank of adorable fiddler crabs.
They apparently shed their exoskeleton and you don’t even need to clean it out the first few days because they like to eat their old bodies! It’s a calcium source for them!
When I am too old to take care of dogs and if I ever am at a convenient point where I wouldn’t be introducing something a cat can mess up into a house, I want fiddler crabs. Maybe some hermit crabs, too.