Radiolaria facts for kids

A group illustration of one of the Radiolarian superfamilies.

Radiolaria are tiny, single-celled creatures that live in the ocean. They are a type of protist, which means they are not animals, plants, or fungi. Radiolaria are like amoebas because they can change their shape. They are special because they build beautiful, hard skeletons, usually made of a glass-like material called silica (SiO₂).

Inside each radiolarian cell, there is a special central capsule. This capsule divides the cell into two main parts: the inner part, called endoplasm, and the outer part, called ectoplasm.

Radiolaria float in the ocean as part of the zooplankton, which are small animals that drift in the water. When radiolaria die, their tiny skeletons sink to the ocean floor. Over time, these skeletons can cover large areas, forming what is known as radiolarian ooze.

These amazing creatures have been around for a very long time, since the beginning of the Palaeozoic era. Their name, Radiolaria, comes from the fact that many species have a radial shape, like spokes on a wheel.

Radiolaria are very important for scientists studying Earth's history. They are useful fossils because new species appear and disappear quickly over time. This helps scientists figure out the age of different rock layers (called strata) and match them up in different places around the world.

Radiolaria are heterotrophs, meaning they get their food by eating other small organisms. However, some radiolaria also have tiny algae living inside them. This is a special partnership called endosymbiosis, where the algae make food using sunlight, and the radiolarian gets some of that food.

How Radiolaria Are Built

The skeletons of radiolarians are often built around tiny spikes or spines. These spines grow out from the main part of the skeleton. Many of these spines can join together to form the outer shell, which is also called a test.

Inside the outer shell, there are often many smaller, round shells, one inside the other. Strong bars or beams connect the outer shell to these inner shells. This design makes the whole skeleton very strong and supportive.

Inside the Cell

Most of the important parts of the cell, like the nucleus and other organelles, are found in the inner endoplasm. The outer ectoplasm is filled with bubbly spaces called vacuoles and tiny drops of fat (lipid droplets). These help the radiolarian float in the water.

Often, the ectoplasm also contains symbiotic algae. These algae are like tiny plants that live inside the radiolarian. They use sunlight to make energy, which provides a lot of the food for the radiolarian cell.

Scientists don't know a lot about living radiolaria. This is because it's very hard to grow them in a laboratory.

Images for kids

• Radiolaria skeletons, artificial colouring.
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  Radiolarian shells are extremely varied. This is just one family, the Cyrtoidea.

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  Shows the cells inside the shells (Report of the Challenger Expedition 1873-76)

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  Important fossils in marine sediments are the hard parts of single celled organisms. Their shells are made out of silica (radiolaria (a, 350µm) and diatoms (b, 50µm); or out of calcium carbonate (foraminifera (c, 400µm) and coccoliths (d, 15µm).

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  Animation of radiolarian diversity 
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  Circogonia icosahedra, a radiolarian species shaped like a regular icosahedron.

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  Anthocyrtium hispidum Haeckel.

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  Like diatoms, radiolarians come in many shapes.

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  Also like diatoms, radiolarian shells are usually made of silicate.

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  However, acantharian radiolarians have shells made from strontium sulfate crystals.

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  A cutaway diagram of a spherical radiolarian shell.

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  Cladococcus abietinus.

See also

In Spanish: Radiolaria para niños