文昌鱼 / Lancelet (amphioxus)

No backbone? No problem! My flexible body helps scientists investigate the ancient blueprint behind yours.
没有脊椎也不怕！我柔软的身体，能帮科学家寻找你身体构造的古老蓝图。

Sources
The amphioxus genome and the evolution of the chordate karyotype
https://www.nature.com/articles/nature06967
Molecular analysis of the amphioxus frontal eye unravels the evolutionary origin of the retina and pigment cells of the vertebrate eye.
https://www.pnas.org/doi/10.1073/pnas.1207580109
Species reference
https://en.wikipedia.org/w/index.php?title=Lancelet

Research context
Lancelets retain a notochord and segmented muscles. Their anatomy and genomes help reconstruct the chordate body plan before vertebrates evolved heads, vertebrae and more complex sensory systems.