Krakken

From Ben10versepedia

The Krakken is a massive sea-creature that lives in the lake Ben visits in "The Krakken". This particular Krakken seems to be a female, since it has a nest and two eggs. There are aquatic species in which the males take care of the young, but this may not be the case with the Krakken, and Ben does refer to it as a she. It is highly territorial and protective of its brood, risking just about anything to defend them and lashing out when its nest is disturbed. It initially attacks Ripjaws until it realizes he is defending the eggs.

The Krakken looks slightly similar to a plesiosaur, possibly being an off-shoot of the species. The main differences between the Krakken and a plesiosaur are that it has two tentacle-like tongues, each with a "mouth" on the end, and large skin-flaps connecting its fore-legs to its body. Also, the fact that it has legs, and very powerful ones at that, is a major difference, since Plesiosaurs had flippers. Also, Plesiosaurs generally had long necks, whereas the Krakken has a shorter neck (relatively speaking).