What people think are Goomy's eyes are actually it's nostrils. It's real eyes are the green circular patches on either side of it's mouth.
Sliggoo's small snail shell-like structure is what becomes Goodra's tail via growth and uncurling.
I came to these conclusions with help from ~DefeatDeception
through my process of drawing realistic pencil sketches of Pokemon. Although I am working an a major project of a realistic Torterra and Turtwig, I am happy with how it's coming along, so before I mat it, I'll probably scan it and submit it here on dA. I DIDN'T MAKE THEM TORTOISES EITHER, HUEHUEHUEHUE.
I think they're helpful little facts, just in cause anyone was wondering or thinking about drawing them.