Rhizopoda are a broad group of protozoan amoeboid organisms placed in the kingdom Protista. They include the naked and testate amoebae, some members of the slime moulds and foraminifera. The latter are almost exclusively marine organisms, either benthic or planktonic. Locomotion is by extension of pseudopodia of varied morphology that are specific to the taxonomic group. Pseudopodial morphology includes broad and fan‐shaped anterior extensions, finger‐like tubular extensions, or a web‐like network, the latter are called rhizopods. The shape of the pseudopodia, and the morphology of the enclosing shell or test, when present, are major defining taxonomic characteristics. The Rhizopoda are important aquatic and terrestrial protozoa at the base of food webs and thus provide a major link in the transfer of energy to higher order consumers. Some are capable of preying on fungi (e.g. large mycophagous amoebae) or other protists and in some cases small invertebrates (e.g. foraminifera).

Key Concepts:

  • The shape and organisation of pseudopodia are among major characteristics used to classify members of the Rhizopoda.

  • However, pseudopodial shape is not a conservative feature; and additional evidence, including fine structure and molecular genetic data, is needed to create a natural classification scheme.

  • The diversity of Rhizopoda is broad, including a wide range in size from small naked amoebae (several microns) to foraminifera (up to several millimetres or larger).

  • Many of the Rhizopoda are free‐living, forming important links in food chains, but others are parasitic or infectious, including some human pathogens (e.g. Entamoeba histolytica).

  • Some aquatic Rhizopoda, among them at least one amoeba and some foraminifera, form algal symbioses, including associations with green algae and dinoflagellates.

  • The foraminifera and some testate amoebae, bearing mineralised shells or skeletons, settle into aquatic sediments when they die and contribute to the palaeontological record of life and the environment over vast geological time periods.

Keywords: biostratigraphy; evolution; microfossils; molecular genetics; Protista

Figure 1.

A lobose gymnamoeba (Chaos carolinense). With permission from Lee et al..

Figure 2.

A lobose testate amoeba (Phryganella nidulus) showing the granular test enclosing the cell and emerging finger‐shaped pseudopodia. With permission from Lee et al..

Figure 3.

Euglyphid testate amoeba (Euglypha ciliata) with filose pseudopodia emerging from a spinose test composed of imbricated siliceous scales. With permission from Lee et al..

Figure 4.

Stereomyxa ramosa, a species in the class Acarpomyxea showing the branching plasmodium and bifurcated terminal pseudopodia. With permission from Lee et al..

Figure 5.

A general diagram of a benthic foraminifer showing the multichambered spiral shell with a small initial chamber (proloculus) at the centre and peripheral halo of granular rhizopodia. With permission from Lee et al..

Figure 6.

A living planktonic foraminifer showing the translucent calcitic shell and radiating spines covered by, and supporting, a network of rhizopodia bearing yellow‐green algal symbionts.



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Anderson, O Roger(Jun 2011) Rhizopoda. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001986.pub2]