A Ciona larva looks like a small tadpole. It has a notochord running the length of the tail, a hollow dorsal nerve cord above it, and a pharynx with gill slits. These are the diagnostic chordate characters. The larva does not feed; it swims for a short period, often hours to a day or two, then settles head first onto a surface.
Metamorphosis then dismantles most of that anatomy. The tail is resorbed, the notochord disappears, and the nervous system is reduced to a small ganglion, leaving the sessile adult that filters water through an incurrent and an excurrent siphon.
The old story that the animal digests its own brain is a memorable overstatement. The larval nervous system is largely reorganised and reduced during metamorphosis rather than consumed as food, and the adult retains a functioning ganglion. Molecular work has confirmed tunicates rather than lancelets as the vertebrates' closest living relatives, a placement that overturned the earlier textbook arrangement.