> A conscious agent believes, desires, wants, feels, etc.
Then, when I just observe how an ant behaves, I can definitely see that he "believes, desires, wants, feels etc."
He sees and/or smells the crumb that I've made while eating a sandwich. He "desires" and "wants" it, runs to it. He "believes" it can lift it and "feels" it can do it. He tries, more than once. Then he has to adjust his belief: the crumb is too heavy. So he gives up trying to lift, now he "believes" he should bite a peace of it. And he does that. Then, he has a new "desire" to carry the bitten-off peace back to the "house" in the hole where other ants are. And he "feels" he can do this, and he will eventually do this. If another ant tries to take the crumb he carries, he will "feel" hat he "has to fight" but he can also "decide" it's "not too interesting" and it's "better to search for another crumb." Now tell me how is that behavior different from a person which is unable to speak, and where you would describe it with "beliefs, desires etc."
What is consciousness without the concept of self, though? "I think, therefore I am" is the basis of how we view human existence, and there is no reason to not think that the concept of self is just another illusion created by our pattern recognizing brain.
Consciousness without the concept of self is general consciousness. Like animals or infants. A consciousness that can experience and react to the environment, but has no idea of itself.
Consciousness with the concept of self is self-awareness. It's a more "advanced" form of consciousness. Where the consciousness is aware that it is conscious.
I might be wrong, but that's how I understand it.
As for the self being an illusion, we don't know for sure, but I think that's the most likely case.
That may be how it's commonly viewed in western philosophy, but some eastern philosophies are closer to the reverse: "I am, therefore I think." Just keep in mind there are currently many living philosophies that conflict with Descartes.
But it's very hard to say why consciousness shouldn't be conflated with self-image in the brain!