Sea urchin & star fish

At work (at the Kieler Forschungswerkstatt) there are a couple of fish tanks with interesting stuff in them. I made these videos ages ago but just thought I’d share them now anyway. I find it pretty fascinating to watch the undersides of sea urchins and star fish! And I read somewhere a while back that they are actually closely related: If you wrapped the segments of a sea urchin downward, you would get a star fish. No idea if it’s true, though, I might just have perpetuated an urban legend? Do you know?