Bernard Heuvelmans 
Kraken and The Colossal Octopus [PDF ebook] 

First published in 2003. From Part One: ‘Our ignorance of the marine world is much greater still. It is such that I do not hesitate to claim that, in the ocean, everything is still possible! Faced with the immensity of Neptune’s realm, a certain degree of gullibility is preferable to blind incredulity. If it was claimed tomorrow that a real mermaid had been captured – not just an ugly manatee, but a creature boasting Marilyn Monroe’s bust and the tail of a coelacanth – the attitude of the zoologist who wished to see it would be much more scientifically justifiable that that of his colleague who would merely shrug the news away. The sea covers more than three fifths of the surface of the globe, but our ships cross it only along rather narrow and fixed paths.’ This book looks at the science behind the stories.