Estuarto is the evolution of Chelanoo. Small numbers of Chelanoo migrate from the salty ocean to the more hospitable fresh water found around river deltas. After many months of acclimatising to fresh water they begin to gradually glide upstream. Here they are exposed to minerals atypical of the ocean, which causes growth first in their shell. Absorbing these minerals by osmosis, the creature itself then grows for the first time since its hatching. Many years following the completion of this slow evolution, the creature finds its way back to the place of its hatching to lay its eggs. Following this, the creatures are rarely seen again.