Radiolaria

Radiolaria are a type of protist that produce intricate mineral skeletons, typically with a central capsule dividing the cell into inner and outer portions, called endoplasm and ectoplasm. They are found as zooplankton throughout the ocean, and their skeletal remains cover large portions of the ocean floor as siliceous ooze. Due to their rapid turnover of species, they represent an important diagnostic tool for identifying geologic time periods.

Classification

Radiolaria are traditionally divided into two groups, the Polycystinea and the Acantharea, based on the form of their internal skeletons. However, recent genetic studies have shown that the Acantharea are more closely related to the Cercozoa and the Polycystinea to the Stramenopiles.

Morphology

Radiolaria have many needle-like pseudopodia supported by bundles of microtubules, which aid in the Radiolaria's buoyancy. The cell nucleus and most other organelles are in the endoplasm, while the ectoplasm is filled with frothy vacuoles and lipid droplets, keeping them buoyant. The radiolarian can often contain symbiotic algae, especially zooxanthellae, which provide most of the cell's energy.

Fossil record

The fossil record of radiolarians is extensive, with the earliest known specimens dating back to the Cambrian period. The siliceous skeletons of radiolarians can remain unaltered for millions of years, and their intricate structures are used for microfossil identification.

See also

• Foraminifera
• Diatom
• Amoeboid

References

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External links

• UCMP Berkeley: Introduction to the Radiolaria

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