Tardigrades!

Update for posterity, in case the link should ever die:

I want a bonny tardigrade to serve me for a steed.
I'd harness him with watercress and provend him with mead.
We'd leave the hillock for the plain, forth to the desert wend;
from each bright globule of his brow a dock leaf I'd prepend.
His limbs, gone leathery with thirst, would lose their lustrous sheen,
and then I would rehydrate him with pulls from my canteen.
His feet would clasp the dunes beneath, his snout survey the sky,
while I, upon his back, sought out our caravanserai.
Unendingly we'd course the earth, our fortune never fixed --
the West Wind gee, the East Wind haw, and him and me betwixt.
My Octopod Bucephalus, my ally and my charge!
I'd do it all, were he less small, or I less sodding large.