how widespread is sentience in the animal kingdom?

psychologytoday | We all know that nonhuman animals (animals) such as chimpanzees, wolves, dogs, cats, and all other mammals are sentient beings. They have "the ability to feel, perceive, or be conscious, or to have subjective experiences." The recent Cambridge Declaration on Consciousness also noted that consciousness is more widespread than some people had previously thought and that certainly all mammals are conscious beings. But what do we know about other vertebrates and invertebrates?

An online debate between Indiana University's Colin Allen and myself was recently held, hosted by the World Society for the Protection of Animals (WSPA) as part of their Sentience Mosaic, that focused on the question, How widespread is sentience in the animal kingdom? You can see the full text here. And, what's great about these debates is that you can also post questions after they are held.