Most often, Cipactli has been described as a sea demon or monster looking like a crocodile, at times showing some toad and fish features.
In Aztec cosmogony, this asexual sea monster is considered as original source, the start from where the cosmos was created. The Aztecs held the belief that the Earth was created from the destruction of this large sea demon, who, in time, was created by the four original gods.
The story of creation, according to the Aztecs, is actually a story of birth, death, and rebirth. When the world is destroyed, it's born again through the sacrifice of one of the gods, and so through the birth of a new sun. However, it's not a story of endless cycles, as you may see in other cultures. For the Aztecs, the universe did have an actual beginning...
In the beginning was the void. Then, the dual god, Ometecuhtli/Omecihuatl, created itself. This god was good and bad, chaos and order, male and female. Being male and female, it was able to have children. It had four, which came to represent the four directions of north, south, east and west. The gods were Huizilopochtli (south), Quetzalcoatl (east), Tezcatlipoca (west), and Xipe Totec (north). These four gods began to create. They created water, and other gods, and the sea monster Cipactli. This was a consuming monster, a jaw at every joint. Cipactli was to become the source of the cosmos in a strange way.
Cipactli’s appetite was insatiable, and as the gods continued to create, they had a problem, their creations would fall into the water and be eaten by the dreadful Cipactli. So the four gods attacked the sea monster, pulling her in four directions. She fought back, biting Tezcatlipoca and tearing off his foot, but at last she was destroyed.
Then Tezcatlipoca and Quetzalcoatl created the heavens and the Earth and everything therein from Cipactli’s body. The creature’s head became the thirteen heavens, its tail the underworld (called Mictlán, which are nine underworlds, to be exact), and its midsection the Earth.
-Vigil, Angel. The Eagle on the Cactus: Traditional Stories from Mexico. Libraries Unlimited, 2000.
-Doyle, D. (2007). Aztec and Mayan Mythology. Yale-New Haven Teacher’s Institute. 2 Feb. 2007.