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There are numerous different sonic universes.
SegaSonic - The games, need I continue
Anime - Sonic the movie. Take place on a planet called freedom and features sonic, tails and knuckles fighting Metal Robotnik and Metal Sonic.
SatAM/Archie - stands for saturday morning. This is the one with Knothole village including the characters antoine, Princess Sally and Rotor (that walrus you mentioned). Currently being shown on POP (Sky 619) at 4:35.
These cartoons were based on the american archie comics.
AoSTH - stands for Adventures of Sonic the hedgehog. This is the one with Scratch and grounder. Might be showing on POP if SatAM isn't.
Prototype - this was advertised but never happened. Check the above link to see images of it.
Underground - images on link above. I don't remember anything about it. For