True symbiotes that need each other to survive might be best represented as two species on one card - and if possible, to have both of their size numbers habitats, and strengths/weaknesses together. It would make a very cramped card, potentially, though, but some CCG cards have very small text on them as it is.
Ones that can survive on their own but do better with compatible species around might need a Keyword and, say, the appropriate Latin of who they are compatible with? (ex, "Symbiote - when within X distance units of a Mammalia card, both cards counts as one unit with the combined Scale #s, food requirements, and weaknesses of both cards.")
Parasites, I think, are a keyword, and can be a standalone card describing what they use as hosts (ex. "Parasite - Preys on Mammalia - Kills target card after X turns.")