The creature is considered sacred by many occupying the 21st Floor. Its appearance closely resembles that of a tortoise with no shell, with the exception of two blowholes in the centre of its 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 Regulars and Rankers to enter its body.
There is a special "jewel" that only grows inside of a Zygaena, which comes from the centre 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 colour. However this "jewel" is also the nutrition for Zygaena's babies. In order to protect the value of the jewel, the Yeon Family stopped all babies from growing by harvesting the Flower of Zygaena.