Going With the Flow One of the simplest animals on Earth lives on the ocean floor. It looks like a small tube about as thick as your finger. It’s a sponge. Scientists used to think sponges


were plants. T ey have roots and parts that look like stems. Sponges are not plants, though. T ey are invertebrates. Sponges don’t have heads, eyes, or


mouths. T ey don’t have muscles or bones. T ey don’t need them. Tiny holes cover all sponges. Water


flows through the holes. It brings in food and oxygen. It carries out waste. Some sponges look like trees.


Others look like fans. Some are very small. Others are very big. You could crawl inside the giant barrel sponge.


red fi nger sponge


yellow tube sponge


SEPTEMBER 2012 11


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