Nibblers

Nibblers are fish like Chain Chomp that appears Paper Mario: The Thousand-Year Door well not really enemies Nibblers attack Mario and his partner if he falls in too a body of water.

Conections to grodus and the X-nauts

Well on the X-Naut moon base in Grodus' room the wall is a Nibblers tank which means that the X-Nauts might have created the Nibblers by fusing a cheap-cheap with a chomp. Or the X-Nauts could have discovered them in a crater on the moon or in the sea area. Any way you look at it the answer comes out the same that the X-Nauts most probably discovered them because after the X-Nauts disappear the nippers go with them and have not appeared in any other games since the thousand year door.