He was part of the Bosporan Civil War during 309 BC, between himself and his brothers, Eumelos having a claim to the throne and the backing of Aripharnes, king of the Siraces.
Not much is known about Prytanis prior to the civil war, but he was the youngest son of Paerisades, and thus last in line of succession, and sided with his eldest brother Satyros when Eumelos launched his rival claim for the throne.
[1] Here, Prytanis held a great funeral for his elder brother[2] and quickly went to Gargaza, taking both the army and royal power.
[3] Eumelos sent envoys to Prytanis, but he ignored them and left a garrison in Gargaza so that he could quickly return to Panticapaeum in order to secure the throne for himself.
[5] Prytanis then took the field against his brother near the Maeotic Lake, but was defeated[6] and Eumelos forced him to turn over command of the army and abdicate in his favor.