Tartaruga is one of the few known Monumentials. It appears to be a moving island, but under the surface of the water it is revealed to be a giant sea turtle. Surprisingly, it was awake when the Nektons encountered it. Even more surprisingly, none of the Guardians seemed concerned with its wakefulness and were fine to leave it roaming the ocean rather than insisting it sleep, unlike the Kraken and the Electric Ray monumentials.
Tartaruga also appears in the episode "Purple Tide", where it eats a jellyfish bloom that has surrounded Quatanui Island.