鳐鱼 / Rays and skates

My broad fins turn swimming into underwater wing-flapping—another use of the paired-appendage toolkit behind your limbs!
我用宽大的鳍在水下扇动前进——你四肢背后的成对附肢工具箱，还有这种创意用法！

Sources
The little skate genome and the evolutionary emergence of wing-like fins
https://www.nature.com/articles/s41586-023-05868-1
Appendage expression driven by the Hoxd Global Control Region is an ancient gnathostome feature.
https://www.pnas.org/doi/10.1073/pnas.1109993108
Species reference
https://en.wikipedia.org/wiki/Batomorphi

Research context
Rays and skates transform paired pectoral fins into broad locomotor surfaces. They provide a striking comparison for how a shared vertebrate appendage toolkit can produce different forms.