The basis of the Keranid body is crystalline molecules that build the core of the cell structure. Being under a constant high energy flow and usage the body needs to be able to endure a lot just to stay in its form.

Since cells do not make copies by renewing they rather build new cells all the time. Water holds the basis for them to survive. As there is no physical food supply they just absorb and reform existing cells, which reduces the overall mass but doesn't change the efficiency.

If the body runs out of energy to maintain its form it goes into hibernation.

Physical food:
Keranids have predator jaws mostly for protection. The jaw is designed to bite and slice, as they choke down whatever it might be. The stomach functions to split down everything into its molecules and use for whatever it has use for. Some it stores, some exit the body via urine. One part of the stomach are chemicals that help to break down and the other is a system of little tentacle like internal life forms that are a part of the body and takes the molecules apart.

As long as it is not a toxin that destroys the cells directly, it would have no effect. Between stomach and neural blood flow is a barrier that selects what can pass through.

The infected earth:
Physical food is an option but not a must. They only eat to maintain the cell count or heal damage taken to the body. The other option that is permanently active is a supply they gather from the symbiotic infection with the earth itself. The system spreads throughout the world and makes it possible to get everything the body needs by hooking up to the system. Connections are at the paws, hands, tail and tongue.

Water:
5L-10L a day is essential to stay functional.

If underwater they do not require any kind of supply. The fur will absorb the water continuously along with the minerals in it. The connection to the infected planet is permanently active while in that state. As well as the body being able to process massive amount of energy because the hair functions as heat pipes and all heat from the core is pushed to the surrounding water. Most of the heat goes to the tail for that.

Keranids used to live mainly in water but the limitation was too great and also limited the interaction with other intelligent life greatly.

Photosynthesis:
They form large plates out of the fur and sunbathe at least once a day. The fur always generates energy from sunlight and takes it as extra source of energy. The lungs filter carbon dioxide and oxygen out of the air to process the photosynthesis.