Grassoni are enormous, semi-mollusks native to the plains of Prall. About 90% percent of the plains are dominated by the Grassoni's "grass segments".
Most of the Grassoni organism is an enormous, disc-shaped mass of flesh that lives about five meters underground. The only protion above ground is the "grass" segment, tall shoot-like plants that have a symbiotic relationship with the animal.
The animal is a fairly simple creature, mainly composed of muscle and fatty tissue. The creature does possess a heart, however.
The animal and the plants share the same air; oxygen produced by the grass segments is transferred to the animal, which in turn transfers carbon dioxide to the plants.
Much of the Grassoni's food is produced by photosynthesis undergone by the grass segments (in return, the grass segments are supplied with shelter and extra water from the animal's tissue).
Once a year, the plant segments will produce bright orange flowers pollenated by Nectarsnatches. Seeds are produced, which germinate into microscopic, planktonic creatures which burrow through the ground eating decaying matter. Eventually this will grow into a Grassoni, which will eventually grow to be over two square miles in size.