The Sargasso is the only known fully aquatic dragon species at the present. It is believed to live on a diet only of seaweed and fish. The Sargasso has no legs, but has two arms and a pair of full wings, likely used for some sort of transportation. Each of these dragons have a several unique crests on their head, and spikes on the arms and back. Similar to the European Dragon, it has a flipper-like crest on its tail. The European Dragon has an arrowhead. It has seemed to have died out in the recent years.
According to modern dragonological research however, the Sargasso dragon is making a comeback. Although they are rare, they are no longer extinct. Another remarkable success in dragonology!
ALSO: The European dragon never died out. The SASD and I continue to see them. They are one of the more common dragons. And what 'flipper like crest' does it have on it's tail?