Estuarto is the evolution of Chelanoo. Small numbers of Chelanoo find a less salty environment more hospitable, spending their time close to river deltas. After many months of acclimatising to fresh water they let 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 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.