Alright, let's start this off right! Pantestudines is the total-group clade to include all extant and extinct species of turtles! They include stem-turtles, and turtles who lack full shells. Stem-turtles are animals who are very closely related to turtles taxonomically, but branch off away from turtles. In other words, they fall in the intermediate space of turtle development, but didn't directly lead to the development of turtles. Some very famous members of the Pantestudine clade are:
The next clade down for turtles is Testudinata!