As always Duolingo sticks to real world application
whats wrong with "sei non una tartaruga"?
"Non" generally precedes the verb.
Tartaruga is such a fun word.
"Turtle" is "tartaruga" in Portuguese too. In Spanish, "turtle" is "tortuga". In French, it's "tortue". I don't know yet what it is in German.
In German it's even funnier, as it means "shield-toad" (Schildkröte) :P