" pikaia and Lancelot please"

Good question. The Lancelet's muscles are configured differently to Pikaia's. They are taller and narrower allowing Lancelets to swim faster; it's likely Pikaia could not do that. There are other morphological differences too, including tentacles on the head of Pikaia, the presence of nine appendages that might be something to do with the respiratory system (lancelets breath through their skin).

While lancelets are considered very close relatives of vertebrates (,molecular biology has given new insight into their position), the status of Pikaia is far less certain; I'm not sure what the current thinking on this is.

It's interesting to note that during the very early development of humans, we too have a notochord and pharyngeal slits.