Amphioxus. Branchiostoma lanceolatum
It sits there as a close relative of the vertebrates, right at the fork in the branch. Interesting group of animals in an evolutionary sense. Boring as fuck otherwise, but like the narwhals, has a song
It's a long way from Amphioxus,
It's a long way to us,
It's a long way from Amphioxus
To the meanest human cuss.
It's good-bye, fins and gill-slits,
Welcome, lungs and hair!
It's a long, long way from Amphioxus,
But we all came from there.
to the tune of It's a long way to Tipperary. Had to bloody sing it in first year zoology lectures.