They form an important part of the marine food web. They act as decomposers, and when they die, their silicone-based skeletons rain down onto the sea floor and make up a lot of the substrate material. Since then, different types and amounts of radiolarians have dominated different eras. Geologists are now using this information in geological mapping. Radiolarians have such a good fossil record because their silicon skeletons preserve so well.
Some radiolarian skeletons have inner and outer sections.
For a 3D image of a radiolarian, click on the picture below. Some radiolarians, like the one below, are bioluminescent. They are able to produce light internally for a variety of purposes. Radiolarians have inspired some amazing biological artists. Included are some of his amazing radiolarian drawings.