Invertebrate
Invertebrate, any animal lacking a backbone. Invertebrates are by far the most numerous animals on Earth. Nearly 2 million species have been identified to date. These 2 million species make up about 98 percent of all the animals identified in the entire animal kingdom. Some scientists believe that the true number of invertebrate species may be as high as 100 million and that the work of identifying and classifying invertebrate life has only just begun. Invertebrates live in a vast range of habitats, from forests and deserts to caves and seabed mud. In oceans and lakes they form part of the plankton—an immense array of miniature living organisms that drift in the surface currents. Invertebrates are also found in the soil beneath our feet and in the air above our heads. Some are powerful fliers, using wings to propel themselves, but others, particularly the smallest invertebrates, float on the slightest breeze. These tiny invertebrates form clouds of aerial plankton that drift unseen thr...