Ethmodiscus is a genus of diatoms found widely scattered throughout the intertropical and temperate zones in the world's oceans.

While in the ocean, Ethmodiscus use buoyancy control to migrate up and down to the high nitrogen depths and return to the surface to photosynthesize.

Additionally, the biological characteristics of Ethmodiscus are an important component in interpreting deep-sea sedimentary richness and distribution.

The species was found by John D. Wiseman and Ingram N. Hendey in 1952 on the deep-sea floor by the H.M.S.

During this time, E. rex was known to rarely be found in the living state in plankton communities.