Camouflage

Winner of the Nebula Award for best novel, 2005Winner of the James Tiptree, Jr. Award 2004Unknown to anyone, two creatures have wandered the Earth for generations. The aliens have no knowledge of each other, but share a residual memory of a mysterious, sunken relic - and an affinity for deep water. One, the changeling, has survived by adaptation, taking the shapes of many different organisms. The other, the chameleon, has survived solely by destroying anything or anyone that threatens it.
Now, finally brought up from the bottom of the sea by marine biologist Russell Sutton, the relic calls to them both .