In Keroro Gunso, axolotl is an alien race similar to the Keronians who live in the planet Axotolon, the 23rd Planet of Gamma. Axolotl was first mentioned by Sumomo, its name is named after the real life amphibian, axolotl, which Sumomo is based on.
They are alien beings that can change different forms at will with neoteny. Sumomo and Nyonyo are the only notable Axolotlian in the series. No other Axolotlian shown in the anime or manga have any role, aside from minor background appearances.
In their natural form, Axolotlians resemble the real-life salamanders that they are named for in the same way Keronians resemble frogs; such amphibian kinship may explain why Keronians adore "Sumomo".
Physically, they have proportions and coloring extremely similar to the Keronians' and the few Axolotlians shown in the series seem to only wear hats covering their heads. Differently from Keronians, they have large crests on the side of their heads and round tails.
- Axolotl at Wikipedia