"If BIONICLE characters do eat (as I think they do), they do it by directly absorbing energy, not by chewing and swallowing as we do (except in very rare cases). They need energy because they are partially organic, but we do not know whether organic protodermis requires any kind of a circulatory system to function. There is no digestive system as we have, there is no waste. So they wouldn't need a circulatory system for that."
"Skakdi are known to chew and ingest their food, choosing to do so over the typical method of absorbing energy, as other inhabitants of the Matoran Universe view this act as repulsive."
Do Skakdi (and Rahi, whom we also know eat BM with their mouty) have digestive systems? Somehow they must dispose of what they put in their mouths? Clearly it's not used to make them grow.
Side question; do MU inhabitants require energy to regrow their organics parts?
Besides Rahi and Skakdi, other species, including Botar's species and Vortixx, posses teeth, I would assume the same case applies to them?