I think the more amazing insight here (not a new one though) is that "head" and "torso" aren't just human categories, they are at the root of some very old gene

I think the more amazing insight here (not a new one though) is that "head" and "torso" aren't just human categories, they are at the root of some very old genes that govern body development for a vast number of species. So starfishes are "heads without bodies" in the sense that they use the molecular/genetic mechanism that in other species shapes the creature's head, but use it here for the entire body.