Perhaps no other animal inhabits as dark part of the human psyche as the shark. There is something deeply primordial about the fear of being eaten alive by a huge razor-toothed monster. But for most of us, fortunately, such a ghastly fate resides firmly in our imagination. Close encounters with the Galapagos' sharks soon alleviate concerns of even the most phobic snorkeler. Indeed, there are only a handful of recorded attacks from the islands, and if you swim by they invariably ignore you or dart off with a flick of the tail. Related to sharks are the rays, which are also rather notorious and over-maligned. Both belong to the group of cartilaginous fishes, as opposed to the bony or teleost fishes, which include most species we normally think of as fishes. Cartilaginous fishes lack true bone, and instead have cartilage (the same stuff that's in our bodies) to make a framework for muscles and organs. They go back a long way. The eariest shark fossils date back at least 300 million years, compared with a mere 120 million years for modern teleost fishes. So when you look at a shark, think of it not as a deadly killer but as a living fossil.