Other forms: chelonians
The adjective chelonian describes turtles and tortoises.
Chelonian, from the Greek chelōnē, "tortoise," is most often used by scientists to specify the biological order that includes all turtles. The main non-profit organization dedicated to the conservation and study of tortoises and turtles is called the Chelonian Research Foundation. If you want to sound extra fancy, try describing your pet turtle as your chelonian companion.