Les ascidies, nos ancêtres.. Ascidians, our ancestors

Et nous en serions bien plus proches que nous le croyons (lien)

The larva of ascidians has a brain but no mouth, so, when it found a rock at the bottom of the sea where to hang on, it digests its now useless brain ! and develops an enormous mouth. And it feeds passively all it life with all which flows to it. Our ancestors, it is said.
And we are closer of it than we believe ! (link)