Sea sponges are considered to be part of the animal kingdom, even though they lack many of the basic characteristics of animals.
Sponges are immobile and do not have organs or true tissues. They survive by pumping water through their cells and filtering it for food particles. Perhaps the most important distinction between sponges and plants is that sponges are heterotrophs, meaning they consume organic carbon rather than creating it.
Sponges are currently the earliest example of animal life that has been discovered in the fossil record. Evidence has been found of sponge colonies which lived over 635 million years ago.
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