Tirtouga resembles a baby leatherback sea turtle. Its body is blue with black spots on the edges of its flippers. Its black shell has six circular indentations in it. It has a black upper beak and a mask that covers most of its head. It has a light blue patch underneath its eyes. Tirtouga's shell is very tough, and it can dive down to depths of as much as 1000 meters. Tirtouga was known to actively hunt for prey to the extent that it would go on land to reach them. Tirtouga lived in the oceans long ago and is now extant only by reviving it from fossils. The people of Alola believe it to be an ancestor of most turtle Pokémon.
Tirtouga has a striking resemblance to a Pokémon-like design which appeared in the April 1997 issue of MicroGroup Game Review.
Tirtouga appears to be based on a baby sea turtle, more specifically, a leatherback. It also may be based on Protostega, a large, prehistoric sea turtle that was smaller than the Archelon that Carracosta may be based on.
Tirtouga may be a corruption of tortuga (Spanish for turtle, tir having a similar phonetic pronunciation to the tur in turtle) or derived from Tortuga (translated as Turtle Island in French and Spanish). It may also be a corruption of tartaruga, Italian and Portuguese for tortoise, seeing as turtles are closely related to tortoises.
Protoga may be a combination of Protostega (an extinct turtle species largest second to only the Archelon, which its evolution is based on) and tortuga.