Arendt agrees that a new name is in order, but says that biologists do not have one prepared because they disagree about whether mouth and anus formation or another key innovation should be used to name the group.
Just as molecular techniques have revealed data that triggered revisions in cell biology, techniques to sequence genes and observe their activity are now challenging long-standing evolutionary scenarios. "At the turn of the twentieth century, embryologists drew what they saw. But their microscopes stunk and they didn't know about genes," Martindale says. "Now we're finally able to look closer, and we're finding that they're often wrong. But if you think about the tools they had, maybe it's more surprising that anything is right at all."