These are called trophic levels https://en.m.wikipedia.org/wiki/Trophic_level

D'oh! Thanks, I completely forgot that this is literally what makes a food chain a food chain.

Hmm, if you had a species of vultures that only fed on apex predators would that give them a higher trophic level? Or what about bacteria that only eat human flesh? It's wild to think of a bacteria at the top of the chain. Does it count if you only partially eat the victim and don't kill them?

Deep sea vent organisms can extract energy from the nutrients and heat from the geothermal vents.

Yeah, life is messy. It’s part of why it is so hard to define what a living thing is. I think of the world as a giant soup of stuff that eats each other. It’s strange to me that humans think they are above any of it. Really, we are right in the middle of it all! :)

If I want to get super-reductive, I think of life as one continuous self-sustaining chemical reaction. It's an accurate, though usually not very useful way of thinking - but I still cherish it, as it reminds me that life and evolution do not obey the conceptual boundaries we set for it. The concept of a "cell" or "individual" doesn't exist in the runtime of physical reality - if we see evolution as optimization process, it's one that can and does optimize across those boundaries.

The weird fish and spiders in caves? And the creatures around volcanic vents?