Zeuglodon is the name given to the colossal creatures which are awakened for the service of Sinderaan.
In the first days of Rhea, the Astral Dragon Nerijah comes to bless the Sinderaan with the knowledge of what the real meaning of the realm is. She brought a pupa of Qroa with herself, which she fertilized with her staff Dora to give it not one, but 7777777 lives. The pupa the became a nest, and as it grew it became many chrysalises. Each Zeuglodon waits in a chrysalis until it is awakened. When awakened, all zeuglodons look same. They need a space of time to discover the water they are surrounded and merge their soul with a body of a creature they select. Then their bodies transform to partially resemble the creature they selected. Once they start evolving, they hear the resonance of all Sinderaan in the waters and select the right one to become one.
When a Zeuglodon is donned by a Sinderaan, the actual body of Sinderaan dies inside the creature and is digested, transforming and merging the soul with the Zeuglodon and become a completely "one living being".
Zeuglodons are so huge that they dwarf the combatuids of the human race, they ar even bigger than the Sentinel form of the Aranok. As weapons, they use all biological shootouts, chemicals, many limbs to grasp, cut, pierce and fight. They are almost impossible hard to destroy due to their bio armor and elemental resistance, unless they want to sacrifice theirselves. They strongly resemble the cause of Nerijah, "to not die".
During the Second Sun, it is discovered that only 3 Zeuglodons remain. All these 3 Zeuglodons were awakened and fought alongside the Apostles to ensure the Second Rebellium occurs and the realm jumps a stage, eventually entering the Third Sun.