Aside from the Latin, the most common term for lying on your back is supine.
Supine, in an anatomical sense, means lying on your back.
Supine isn't an animal, it's a medical/anatomical term for face up. If you lay on your back, then you're in a supine position. Face down is prone position.
ap supine
"supine" means lying down.
ap supine
Supine is the medical term meaning lying down facing up.
The word "supine" does not appear in Orson Scott Card's novel "Ender's Game." It is possible that you may have encountered the term in a different context or source.
Lying supine means lying on your back (supine is on your spine).
semi supine or prone
Lying supine means to lay on your back with your front up and your legs in the air as if riding a bicycle, i.e. Supine Bicycle
I was lying in my be and I was in the supine form.