It is the same Turtler. Halfshell came from the future and made a deal with Turtler in order to restore his crew (and at the same time, restore the other's 'crew'). Halfshell claims descendant from Turtler. They secure the Angolmois from Galvatron for this purpose, which not only powers up the Seacons, but gives them robot forms (which the Seacons previously didn't have). Halfshell in the meantime is using the time and the tech to revive his own crew while proclaiming himself as a god above kings (God Neptune vs King Poseidon)-- while Galvatron is still in the midst of his transformation.