What are 'living fossils' and which species have barely changed in millions of years?

The answer

Living fossils are species that have remained morphologically unchanged for millions of years. The coelacanth, thought extinct for 66 million years, was rediscovered alive in 1938 off South Africa. Horseshoe crabs have remained essentially unchanged for 450 million years - predating dinosaurs by 200 million years. Their blue copper-based blood is used in pharmaceutical testing worth $60 million annually. Nautiluses have maintained their coiled shell design for 500 million years. The ginkgo tree, unchanged for 200 million years, is the sole surviving species of an entire plant division. Tuatara reptiles of New Zealand retain a 'third eye' (parietal eye) from a lineage that diverged 250 million years ago.