This is a mothra Tamagotchi that was released in 1997 for the Mothra movie. I currently have this blue one and the green version.
The Mothra has a very cute evolving process behind it. You must first succeed in getting the right grub that will evolve into one of the Mothra characters or you will be stuck as a grub.
There are special characters in this tamagotchi, my favorite which is Godzilla. They are secret characters that can be achieved only if mothra leaves an egg when she leaves.