Going With the Flow Deep in the sea, a small, colorful tube curves


up from a rock. White threads glue it in place. Its stiff body doesn’t sway in the water. It looks like a plant. It’s not. Meet the sponge, one of the simplest animals on Earth. It belongs to the phylum Porifera. More than 5,000 diff erent kinds of sponges


exist. T ey live in nearly every ocean habitat. It’s easy to see why scientists once thought sponges were plants. Some look like trees or bushes or fans. A breadcrumb sponge covers rocks like a carpet. Like old bread, it can crumble into pieces when touched. Sponges can be soſt and squishy or they can


be hard as a rock. Some sponges are as small as a grain of sand. T en there’s the giant barrel sponge. A diver could hide inside it. Despite these diff erences, all sponges have


common characteristics. T ey don’t have heads, eyes, or mouths. T ey don’t have stomachs, muscles, or bones. T ey don’t need them. A sponge’s body acts like a filter. Seawater


flows through tiny holes called pores. As water goes in, the sponge gets food and oxygen. As water goes out, it carries away waste. A sponge doesn’t need to move to survive.


red fi nger sponge


yellow tube sponge 5


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