The formation of a notochord, and then a backbone was a big step in evolution. Tunicates which produce “tadpole” larvae are well represented in the glistening chunks of sea pork, knobby potato-like solitary forms or sea grapes. Tunicates absorb their notochords and sit like a sponge on the bottom. Not so with an amphioxus, which retains its notochord.
AS-25 CHORDATE ASSORTMENT:
Includes non-vertebrate chordates: solitary, colonial, and encrusting tunicates and amphioxus