Ok, was out of town and could not buy one. I know it was NOT a cana, I know what they look like. It had a shell that looked exactly like a brigss/diffusa but was twice as big as a full grown one, there were several in the tank. Only saw wild striped large ones. I've had brigss 2 years old that were only half the size of these guys. What could they be (they were at a walmart)?