This made me think of the underside markings you drew:
This made me think of the locomotive pattern you described:
But overall, this one looked most like the picture you drew. They don't show him swimming, but I assume he moves like the rest of them:
So how the heck a flatworm or a nudibranch gets airborne is anybodies guess. There are loads of species and some of them are more or less transparent.
Closest match I could come up with.
Edit to say closely related new species? Helium huffer? Something that would have to have natural buoyancy with the atmosphere to move like that.
Edited by Ilikebluepez, 27 February 2011 - 11:17 AM.