Rhizaria
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The Rhizaria are a major line of protists. They vary considerably in form, but for the most part they are amoeboids with filose, reticulose, or microtubule-supported pseudopods. Many produce shells or skeletons, which may be quite complex in structure, and these make up the vast majority of protozoan fossils. Nearly all have mitochondria with tubular cristae. There are three main groups of Rhizaria:
| Cercozoa | Various amoebae and flagellates, usually with filose pseudopods and common in soil |
| Foraminifera | Amoeboids with reticulose pseudopods, common as marine benthos |
| Radiolaria | Amoeboids with axopods, common as marine plankton |
A few other groups may be included in the Cercozoa, but on some trees appear closer to the Foraminifera. These are the Phytomyxea and Ascetosporea, parasites of plants and animals respectively, and the peculiar amoeba Gromia. The different groups of Rhizaria are considered close relatives based mainly on genetic similarities, and have been regarded as an extension of the Cercozoa. The name Rhizaria for the expanded group was introduced by Cavalier-Smith in 2002, who also included the centrohelids and Apusozoa.