If There Are Things Like This Underwater What Else Is there?

Prehistoric Frilled Shark was thought to be extinct until they found one in Japan in 2007. They live 600 meters or more under the sea. My whole thing is if they thought this was extinct for this long what else to we think is extinct or we haven't found that can benefit or hurt the population? When we refer to aliens we think of intelligent creatures but who will destroy us or benefits us but did we ever consider the possibility that they would just be like regular animals? And did we ever think we were not the most intelligent life forms on this planet? until we explore this WHOLE world we are NOT ready for space travel.

we really are not