I agree with you that the “structure of suffering” is likely to be represented in the neurons of shrimp. I think it’s clear that shrimps may “suffer” in the sense that they react to pain, move away from sources of pain, would prefer to be in a painless state rather than a painful state, etc.
But where I diverge from the conclusions drawn by Rethink Priorities is that I believe shrimp are less “conscious” (for a lack of a better word) than humans and less their suffering matters less. Though shrimp show outward signs of pain, I sincerely doubt that with just 100,000 neurons there’s much of a subjective experience going on there. This is purely intuitive, and I’m not sure of the specific neuroscience of shrimp brains or Rethink Priorities arguments against this. But it seems to me that the “level of consciousness” animals have sit on an axis that’s roughly correlated with neuron count; with humans elephants at the top to C. elegans at the bottom.
Another analogy I’ll throw out is that humans can react to pain unconsciously. If you put your hand on a hot stove, you will reactively pull your hand away before the feeling of pain enters your conscious perception. I’d guess shrimp pain response works a similar way, largely unconscious processing do to their very low neuron count.
I believe the Scramblers from blindsight weren’t self aware, which means they couldn’t think about their own interactions with the world.
As I recall the crew was giving one of the Scramblers a series of cognitive tests. It aced all the tests that had to do with numbers and spatial reasoning, but failed a test that required the testee to be self aware.