Zygaena

Zygaena is a massive Shinheuh used as a "living arena" for team tests on the 21st Floor.

The creature is considered sacred by many occupying the 21F. It's appearance closely resembles that of a tortoise, with the exception of two blowholes in the center of it's belly and back, a long stingray-esque tail, two horns and a mouth full of sharp teeth. It periodically flips over, in order to "sunbathe". Whenever it surfaces, Zygaena will blow water through one of its blowholes. Its innards are accessible through the two blowholes, and provide more than sufficient space for a party (such as Ja Wangnan and his companions).

There is a special "jewel" that only grows inside of Zygaena, which comes from the center of "Zygaena's Flower." It is extremely valuable, as it grows only inside of Zygaena, and is considered one of the best jewels due to its beautiful color. However this "jewel" is also the  nutrition for Zygaena's babies. In order to protect the value of the gem, the Yeon family stopped all babies from growing by harvesting the Flower of Zygaena.

Urek Mazino and Yuri took a baby away from Zygaena in order to make the gem more common in the future.