Meaning of すっぽん in Japanese

Definition of すっぽん

すっぽん(suppon) · スッポン(suppon) 【鼈】

(n) Chinese soft-shelled turtle (Pelodiscus sinensis); soft-shelled turtle (Trionychidae)
月とすっぽん。
They are as different as day and night.

すっぽんぽん(supponpon)

つきとすっぽん(tsukitosuppon) 【月と鼈 ·月とすっぽん】

(exp) like chalk and cheese (superficially similar, but completely different) (the moon and a turtle shell are both round, but they are otherwise completely different); like day and night; like the difference between heaven and hell

すっぽんたけ(suppontake) · スッポンタケ(suppontake) 【鼈茸】

でも、ジェンの家いえのベランダにいたいるヴィンスは上半身裸じょうはんしんはだか。いやーいいえ、もしかしたらすっぽんぽんだったかもッ！

However, Vince, on Jen's house's veranda, was naked from the waist up. He might even have been starkers!