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Marine Animal Encyclopedia

Ethmodiscus rex

Of the 10,000 species of diatoms alive today, Ethmodiscus rex is the largest. It is a single cell with a rigid cell wall, called a test, which is impregnated with silica and covered in regular rows of pits. The test is made up of two disk-shaped halves, called valves, which fit tightly together. Because each diatom has a unique test, Ethmodiscus rex can be easily identified in the fossil record. It is found in rocks that date from the Pliocene and the fossils can be up to 5 million years old. Ethmodiscus rex need to remain near the water surface in order to utilize the Sun’s energy for food, which they do by transforming the products of photosynthesis into oily substances that increase their buoyancy. Ethmodiscus rex can reproduce sexually but, if conditions are favorable, it multiplies rapidly, simply by dividing into two. Over a 10-day period, one individual Ethmodiscus rex that divides three times a day can have over 1.5 billion descendants.

  • Group Diatoms
  • Diameter – in (2–3 mm)
  • Habitat Warm, nutrient-poor water
  • Distribution Open ocean worldwide