It's likely that these species evolved from others that were closer to the surfa...

Renaud on Dec 27, 2014 | parent | context | favorite | on: Unexpected Life Found in the Ocean's Deepest Trenc...

It's likely that these species evolved from others that were closer to the surface. You also see that from species that live deep in caverns. They often have non-functional eyes, remnants from the time when their ancestors were living outside.