The Encyclopaedia Britannica Interactive Science Book: Under the Sea is an 80-page, brilliantly illustrated book for people of all ages designed for use with the SD-X Interactive Reader (sold separately). The book is part of a six-book library. The books are available separately and also are sold in sets of three and a set of six.The SD-X Interactive Reader is a battery-powered pen that reads text on the book pages and also offers audio content such as facts and sound effects. The Reader works only with the six Encyclopaedia Britannica Interactive Science Library books. Each book has two hours of audio content.The Encyclopaedia Britannica Interactive Science Book: Under the Sea is an extensive look at the watery world that covers more than two-thirds of Earth. Starting with a chapter on ancient sea life, the book provides an extensive look at algae, water plants, invertebrates, fish, amphibians, reptiles, and water mammals. The book looks at the world under water from every angle�all accessible in an enhanced format using the SD-X Interactive Reader.