Invertebrates and Sentience

I have never thought that most invertebrates possessed sentience, at least not in the sense that they could feel pain or experience pleasure, but this essay by Rick Bogle suggests that there is a lot that I don't know and perhaps will never know about animals and their ability to be self-aware.  Regardless of whether I can prove that an insect or oyster is capable of being in pain, or experiencing fear, they do seem to be capable of higher order sentience and deserve the benefit of the doubt when it comes to how we as humans treat them.  Beware of anyone who suggests taking the sentience argument and applying it to plants, as sentience requires the ability to feel or perceive with a mind, nervous system, etc.  I love plants, but they don't have minds and as far as anyone knows, they cannot experience pain or pleasure.