Tunicates are chordates, not vertebrates. All vertebrates are chordates, not all chordates are vertebrates. Square/rectangle kind of thing. But among invertebrates, they are the closest relatives to us.
From the pic, I would say Tunicates. The question about demand depends on their survivability in home tanks, which for tunicates is generally pretty poor.
Get them to some people who feed a lot, and see how they do.