It's a little difficult to believe that this sac-like creature with two openings is a ‘near-relative’, but anatomical and molecular evidence shows that tunicates descended from our own ancestors that lived perhaps 550 million years ago. Tunicates have the four features of phylum chordata (notochord, pharyngial gills, dorsal nerve cord, and post-anal tail) but to see these features you will have to follow the full life-cycle of the animal. As larvae, tunicates are free-swimming microscopic animals such as the stained specimen seen under the microscope in this photo.

After swimming in the ocean for a few days, the tadpole larva settles to the bottom and metamorphoses into a sac-like animal that feeds by filtering plankton out of the sea. You can observe this metamorphosis, along with the fascinating heart of the tunicate which moves blood by ‘wringing out’ in our film Branches on the Tree of Life: Chordates.