They have a central nervous system, with three ganglia: http://www.manandmollusc.net/advanced_introduction/bivalve_n...

If you look carefully, it is very similar to the neural system in any bilateral https://www.britannica.com/science/nervous-system/Diffuse-ne... . It is twisted following the deformation of the body inside the shell. Compare it with https://entomology.unl.edu/charts/nervous.shtml

In our central nervous system one of the ganglia grow tooooooo much. Moreover, the olfactory part of it grow tooooooooooooooooooooooooo much.

How can we define what "capable of consciousness" is? As we become a species closer to exploring the vast cosmos, we have to be humble in our assumptions of what consciousness or life is. It's quite a Copernicus error to think that humanity is the center of relative consciousness to compare against. What consciousness is may be entirely incommensurable - which would be a serious error in our discovery of what else exists in the universe.

There's a lot of wisdom in Star Trek: TNG, and it feels more prudent than ever to contemplate these lessons as we near the point of becoming space faring species.