Well, its name hasn't been out yet, but I recognize it as Kraken, the giant squid. It was at the sea. If it was manticore, it'd be another beast of the combination of a lion and a scorpion(NOT The Piraeus' lion - Το Λιοντάρι του Πειραία in Greek -in GoW3). As for the other name, I don't know.
I haven't studied the Greek Mythology for nothing. Unfortunately I never have had the chance to read the Titanomachy as to learn about the titans, and the other beasts.