heterocercal

adjective

het·​ero·​cer·​cal ˌhe-tə-rō-ˈsər-kəl 

1

of a fish tail fin : having the upper lobe larger than the lower with the vertebral column extending into the upper lobe

2

: having or relating to a heterocercal tail fin

Word History

First Known Use

1838, in the meaning defined at sense 1