If you mean LA tartaruga it is like any other noun. You have to memorize. With rare exceptions, the gender of the word does not depends on the biological gender of the animal.
If you mean un animale you have learned that word animale is masculine. It will always take masculine articles, regardless of the gender of the word for the animal or the biological gender of the animal
It sounds like "tart-a-ruga" not "tar-tar-uga." Listen carefully to the word by itself, not just use in the sentence. Doesn't this seemsto be the way the voice is pronouncing tartaruga. How do native Italians pronounce it? The Duo-voice has an interesting way of pronouncing the "t"s. The Duo-voice also seems to trill the "r" a bit.