Download the book This book is devoted to the study of invertebrate animals. While most people associate the word "animal" with fish, amphibians, reptiles, birds, and mammals, 90% of the animal species on earth are invertebrates, i.e., they have no backbone. Protozoans and invertebrate animals are found world-wide, from the bottom of the oceans to the the rain forests, ice caves, and our own back yards. Many invertebrates still reside in the oceans, while others dwell in our houses, back yards and gardens, in ponds and streams, and on the menus in seafood restaurants. Holders's book represents a traversal of several dozen familiar and not-so-familiar animals without backbones whose ancestors date back to the Cambrian period 500 million years ago.