Rhizaria Cavalier-Smith 2002


Rhizaria comprises several very large and diverse groups of amoebae, flagellates and amoeboflagellates. Many of these are ubiquitous in nature and important predators in many environments.

The amoeboid members of the group tend to produce fine pseudopodia, varying as simple, branching, or anastomosing patterns, often supported by microtubules in those groups examined by electron microscopy. Many rhizaria produce shells or skeletons, which may be quite complex in structure, and these make up the vast majority of protozoan fossils. Nearly all rhizaria have mitochondria with tubular cristae.

Rhizaria descend from a heterotrophic eukaryote ancestor with two flagella. They appear to share a common ancestor with Stramenopiles and Alveolates forming part of the SAR (Stramenopiles+Alveolates+Rhizaria) super assemblage.

There are three main groups of Rhizaria:

  • Cercozoa: Biciliated and/or amoeboid, usually with filopodia;
  • Foraminifera: Amoeboids with reticulose pseudopodia, common in marine habitats;
  • Radiolaria: Amoeboids with axopods, common as marine plankton.