The Sea Sponge

The only reported multicellular creature with not only no brain (like a jellyfish or starfish), but also with no neurons at all distributed throughout the tubular body, sea sponges rely on inflow of water to receive nutrients as it stands rooted in place.  Still, it is said to react to stimuli like light (visual) or touch (tactile), such as by contracting at the point of impact.  Found in the epipelagic zone all the way down to the distant trenches of the hadalpelagic zone, this organism is even more unlike humans when it comes to neuroscience than other ocean animals like the aforementioned sea star.  It is thus far a unique peculiarity among catalogued organisms.

A whale has a brain, like a dolphin and a shark have a brain.  A jellyfish has no brain but still has neurons diffused throughout its body.  A starfish as a nerve ring around its mouth with a protruding radial nerve for each arm.  Sea sponges possess none of these things.  Moreover, they lack all organs, such as those for digestion or respiration, not just those participating in neurological activity.  Even coral is supposed to have more of a nervous system than none at all despite its own absence of a brain!  According to professionally popular contemporary scientific stances, it is not as if a nervous system seems to be necessary whatsoever to have mental experience, at a minimum not in all animals.

You can of course never see a consciousness by looking at a body, including the brain or extended nervous system of an applicable organism, with only the outward behaviors making it genuinely appear as if something is conscious.  Science is thus irrelevant to the core metaphysics of consciousness in this sense, for any mind is an immaterial, invisible thing no matter its integration with a body.  One's own consciousness is directly experienced.  That of other biological things can only have the epistemological appearance of existence.  All sorts of creatures still act is if they really do have some degree of perception of the kind I as a being relate to.

In the sea sponge, once again, there is something with a physical body that still acts as if it is conscious, yet there is not a trace of a nervous system.  Is it conscious?  It is impossible for a non-telepathic, non-omniscient observer to know.  It certainly would seem that the sea sponge has some sort of mind, though.  The same epistemological limitation that prevents one from knowing if plants or AI or other people are conscious is there.  As far as sensory observation suggests, the sea sponge probably does have a mind, whatever its actual experiences would actually be like.

Like so many other animals, examples being roaches with a ganglion in both the head and another in the abdomen and octopi with their focused clusters of neurons (like miniature brains) for each arm, sea sponges do not share the human style of nervous system.  If they truly do have minds, then having a consciousness without a specific kind of correlative nervous system is not only logically possible (it does not contradict any necessary truths like axioms and thus at least could have been true), but it is also already the case among some members of the animal kingdom.  There is already absolutely no logical necessity in a mind having or not having a corresponding material brain or other neurons.  With the phenomena we can observe, there seems to also be no contingent, happenstance scientific necessity with this in the particular laws of physics that apply on Earth.