With thousands of relatively large and beautifully presented photographs, this book provides the greatest possible coverage of selected groups of the enormous variety of marine invertebrates in a single volume. It is primarily aimed to assist people who have a keen interest in the small animals they encounter in the sea other than fishes, to find their scientific names or where to classify them. Presented here are the species one is likely to see when diving or snorkeling in the sea, as well as those that are traded in the aquarium industry. Most species occur on shallow reefs in tropical seas, with the greatest species diversity in the Southeast Asian regions.