I agree that this is huge, but it's also depressing. A lot more needs to be done.

Multiple groups of animals do fail certain, or even likely all, criteria. For example, sponges do not have neurons and therefore fail criteria 1 - 3. Although I'm not aware of tests of 4-8 in the sponges, it seems reasonable to suppose that the lack of a nervous system would also preclude endogenous neurotransmitter systems and many of the behavioral criteria.

Importantly, it is not just the number of criteria but also which criteria are fulfilled when considering the likelihood of pain or sentience. Some criteria provide more important evidence for sentience than others. In particular, criteria 2/3 and 5 have been considered important evidence by many philosophers and scientists. The roundworm, C. elegans, fails criterion 2 according to Irvine (2022); we can have reasonably high confidence that this failure is not due to an absence of evidence, but rather evidence of absence, given that we have a complete connectome of the C. elegans nervous system (302 neurons per animal). The fact that all adult insects fulfill criterion 2 with very high confidence, and that we find fulfilment of criterion 3 across the Holo/Hemimetabola split (suggesting the potential for broad taxonomic conservation of this criterion), is a meaningful distinction between these animal groups (at least to me, in the context of this framework).

Irvine E (2022) Independence, weight, and priority of evidence for sentience. Animal Sentience 32 (10). DOI: 10.51291/2377-7478.1724.

This comment is representative only of MRB's opinions and expertise, and not the other post/publication authors.

(Not an animal scientist or a scientist of any nature btw!)

I'd guess sessile animals (e.g. mussels) fail (at least) motivational tradeoffs and analgesia preference.

Nitpicky feedback on the presentation:

If I am understanding it correctly, the current format of the tables makes them fundamentally incapable of expressing evidence for insects being unable to feel pain. (The colour coding goes from green=evidence for to red=no evidence, and how would you express ??=evidence against?) I would be more comfortable with a format without this issue, in particularly since it seems justified to expect the authors to be biased towards wanting to find evidence for. [Just to be clear, I am not pushing against the results, or against for caring about insects. Just against the particular presentation :-).]

After thinking about it more, I would interpret (parts of) the post as follows:

• To the extent that we found research on these orders O and criteria C, each of the orders satisfies each of the criteria.
• We are not saying anything about the degree to which a particular O satisfies a particular C. [Uhm, I am not sure why. Are the criteria extremely binary, even if you measure them statistically? Or were you looking at the degrees, and every O satisfied every C to a high enough degree that you just decided not to talk about it in the post?]
• To recap: you don't talk about the degrees-of-satisfying-criteria, and any research that existed pointed towards sufficient-degree-of-C, for any O and C. Given this, the tables in this post essentially just depict "How much quality-adjusted research we found on this."
• In particular, the tables do not depict anything like "Do we think these insects can feel pain, according to this measure?". Actually, you believe that probably once there is enough high-quality research, the research will conclude that all insects will satisfy all of the criteria. (Or all orders of insects sufficiently similar to the ones you studied.)
  [Here, I mean "believe" in the Bayesian sense where if you had to bet, this is what you would bet on. Not in the sense of you being confident that all the research will come up this way. In particular, no offense meant by this :-) .]

Is this interpretation correct? If so, then I register the complaint that the post is a bit confusing --- not particularly sure why, just noticing that it made me confused. Perhaps it's the thing where I first understood the tables/conclusions as "how much pain do these types of insects feel?". (And I expect others might get similarly confused.)

What indicators of consciousness do you expect mammals and birds to have that insects don't? (Edited to avoid suggesting I'm only asking about the criteria in this post.)

I think criteria 5-8 suggest it's not mere nociception. Of course, they might not establish consciousness, but what more do you expect to do so?

Personally, I'm very sympathetic to Luke Muehlhauser's views in that report and, in particular, illusionism and AST (he doesn't explicitly endorse AST, but I think he said it was the closest attempt), and I still don’t think they rule out insect consciousness or imply we should assign it very low probability. He gave fruit flies 10% and 25% probabilities of consciousness in that report, with 25% closer to his actual views at the time. This seems too high to completely ignore.

I fail to see any lack of distinguishing as I do not see any claim on suffering or capacity to suffer in insects, only on insects' abilities to feel pain.

How physical pain relates to subjectively perceived suffering is a whole other topic, and as far as I can tell no subject to this review. (Though I've only read this post, not the review itself.)

I do see that pain-feeling is usually perceived as something innately suffering-inducing, and I see why that's the case. If pain is not somewhat negative for the organism experiencing it, why would that mechanism establish itself across whole species in the first place? Could be that pain in insects acts merely as a reflex trigger and no experience/suffering in the moral sense is involved at all, but I really argue that this is a whole other claim and topic.

The Open Phil report you linked shows quite well how little we know and how complex this issue is, and that jugdements rely heavily on claims and intuitions due to lack of understanding. 

So as we do not really know how the ganglions of insects (let alone our brains) work and what consciousness or conscious experience really  is about, I' be very careful with making definite claims about the suffering capacities of other species. 
As far as I can tell, the authors of this review made a good job of evaluating the physical ability of insects to feel pain. This is but the first step to assign moral patienthood to insects; it's a necessary, but not sufficient criteria. 

The likelihood of an organism to be able to suffer is significantly higher if that organism is known to feel pain. I personally tend to err on the worse case and assume  pain-feeling organisms are suffering, rather than risk neglecting substantial suffering as the odds seem high enough. (But that's just my personal take.)

I see how the concepts get mingled up inappropriately, but I would not go as far as to demand a clarification on that from any scientific publication dealing with pain (in organisms other than human), especially since there is no sufficiently backed-up concept of consciousness or moral patienthood. In my opinion arguing about wether pain-feeling and suffering can be used anagolous should happen, but it's probably not the responsibility of the authors here. 

Vasco - thanks so much! Sajedeh did a wonderful job with the tables (as well as many other great figures in the publication itself).

Rethink Priorities has an interdisciplinary team working on the many complexities of moral weight (including how important to consider neuron numbers). I know more work will be coming out from that team in the next two weeks on this topic, which I'm sure they can speak about more elegantly and critically than I can.

You can follow that project here: https://forum.effectivealtruism.org/s/y5n47MfgrKvTLE3pw

This comment is representative only of MRB's opinions and expertise, and not the other post/publication authors.