From the roots site "chel- = turtle, tortoise".
chelonian

SYLLABICATION: che·lo·ni·an
PRONUNCIATION: k-ln-n
ADJECTIVE: Of, relating to, or belonging to the order Chelonia, which includes the turtles and tortoises.
NOUN: A reptile of the order Chelonia.
ETYMOLOGY: From New Latin Chelnia, order name, from Greek kheln, tortoise.