There's the Mouse!

Take a look at the brazilian version called saci

http://en.wikipedia.org/wiki/Saci_%28Brazilian_folklore%29

Those are also featured at some point in one of the books in the Narnia series! The Voyage of the Dawn Treader, I believe...

They were called "Duffers" in The Voyage of the Dawn Treader: http://en.wikipedia.org/wiki/Duffer_%28Narnia%29

It's been twenty years or so since I read that book; amazing, how quickly it comes back.

That's a Dufflepud! From Cronicles of Narnia!

I believe CS Lewis also called them monopods.
They were under a curse of invisibility.

It’s been twenty years or so since I read that book; amazing, how quickly it comes back.

Well it's about time to pick it up again. Or better yet the whole series. There is much in the Chronicles that is written for adults; I've read the whole series a number of times (each of the books can be finished on a Sunday afternoon) and something new hits me every time.

A sciopod is also featured in another book, 'Baudolino', by Umberto Eco, a historical fiction novel based partly on early stories of the kingdom of Prester John in the 13th century. Not quite reading material for adolescents, though I remember reading "The Name of the Rose" in high school. For anyone interested in medieval history, Umberto Eco's novels are great reads.