supernumerary

https://doi.org/10.1351/goldbook.11269
Exceeding the usual number; thus, in anatomy, anomalies such as a sixth finger on one hand or a third nipple (in a human).
Source:
PAC, 2016, 88, 713. (Glossary of terms used in developmental and reproductive toxicology (IUPAC Recommendations 2016)) on page 809 [Terms] [Paper]