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Kingdom Animalia

With over 2 million species, Kingdom Animalia is the largest of the kingdoms in terms of its species diversity. But when you think of an "animal", what image comes to mind? While mammals, birds, reptiles, amphibians, and fish are the most familiar to us , over half of all the animal species belong to a group of animals known as arthropods. Arthropods include animals such as centipedes, crabs, insects, and spiders. And with over a million species of arthropods, this means that the majority of animals species come from a group of critters that give most folks the creeps!

So, what exactly is an "animal"? With so much diversity among different animal species, it's difficult to imagine what they all might have in common. First, animals are "multicellular" (composed of many cells). In most animals, these cells are organized into tissues that make up different organs and organ systems. Second, all animals are heterotrophs (= "other feeder"), meaning that they must get their food by eating other organisms, such as plants, fungi, and other animals. (Plants are referred to as autotrophs or "self feeders") because they produce their own food by the process of photosynthesis.) In addition, all animals require oxygen for their metabolism , can sense and respond to their environment, and have the capacity to reproduce sexually (though many reproduce asexually as well). During their development from a fertilized egg to adult, all animals pass through a series of embryonic stages as part of their normal life cycle. Though frogs and humans don't look very much alike, we share many features in common during our embryonic phase.

Last modified October 15, 2011 by Jennifer Bergman.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA