Chlorophyll

Chlorophyll was a pigment found in almost all plants.

Tythonians fed upon chlorophyll and mineral salts. Due to their large size, they required large quantities of it. They soon depleted the small amount present on their native planet, Tythonus.

Erato was sent as an ambassador to the chlorophyll-rich Chloris. There, Adrasta imprisoned him for fifteen years, after which he secured a deal in which Tythonus would receive chlorophyll in return for metal. (DW: The Creature from the Pit)