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 Jigena, 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.

Plot Summary
The objective of Ja Wangnan's team is to retrieve Zygaena's Flower from inside Zygaena. Upon entering the beast and finding the flower at the start, they encounter a man who's back is tattooed with the Walhaiksong's symbol and the name "Mazino" emblazoned directly above it. It is possible that the reason this simple retrieval test was set as the final test of the 21F was because the team would have to deal with Mazino in some form, who is ranked 4th in the Tower, and the strongest active Ranker.