Tortolla is the good guy turtle, a quest giver, and apparently a demigod and ancient guardian. (Note: My facts may be utterly wrong here.)
Nemesis is the bad guy turtle. I’m not sure what his story is.
There’s also another bad guy boss-type turtle who looks like Nemesis in the goblin starter area named Volcanoth.
Both Tortolla and Nemesis/Volcanoth have new, very cool looks with huge shell spikes, horns, and – in the case of Nemesis/Volcanoth – lava and an active volcano.
Everybody and their mother is going to be asking about taming these turtles. Unfortunately, none of these three can be tamed.
If you already have Ghamoo-Ra tamed, your pet will automatically switch over to use the new look.
The volcano turtle look of Nemesis and Volcanoth is a little harder to come by. But there is a new level 81 rare elite beast named Terrorpene who roams around the Throne of Flame in Mount Hyjal.
I can’t get a good model shot of Terrorpene yet – his lava doesn’t render quite right in the model viewer – but the Petopia community has taken some great screenshots. The one above is courtesy of Vephriel.
Terrorpene in his natural habitat, courtesy of nirvana:
Terrorpene in Stormwind, courtesy of Wain:
Terrorpene with excited worgen, courtesy of inico:
As you can see, this is one photogenic volcano turtle! For more screenshots, check out the Petopia community thread.