"""The coconut-carrying behavior makes the veined octopus the newest member of the elite club of tool-using animals—and the first member without a backbone, researchers say."""
What about hermit crabs, trap door spiders, and those crabs that build refuse that they find on their shells as camo?
In each of these cases the organism is using an external object(s) as a form of shelter/protection/camo, in the same way the octopus is. While we are more accustomed to them as they are common, there seems to be very few differences in behavior. We are simply seeing the first generation of a new trait amongst some octopi. Of course any new trait, especially one as nifty as this is cool, it seems like a stretch to call them the first invertibrate tool-user.