Two billion years ago our unicelled ancestors parted genetic company with the plants. By accident of energetics and heritage, large plants now live their lives fixed in place. Animals bolster the argument on the positive side, except for the immobile minority like sponges and clams that support it on the negative. A billion years ago, before brains or eyes were invented, when the most complicated animals were something like hydras, double layers of cells with a primitive nerve net, our progenitors split with the invertebrates. Now both clans have intelligent members.
Cephalopods are the most intellectual invertebrates.
Most mollusks are sessile shellfish, but octopus and squid are highly mobile, with big brains and excellent eyes. Evolved independently of us, they are different. The optic nerve connects to the back of the retina, so there is no blind spot. The brain is annular, a ring around the esophagus. The green blood is circulated by a systemic heart oxygenating the tissues and two gill hearts moving depleted blood.