Rhizopoda

Abstract

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.

close

References

Adl MS, Simpson AGB, Farmer MA et al. (2005) The new higher level classification of eukaryotes with emphasis on the taxonomy of protists. Journal of Eukaryotic Microbiology 52: 399–451.

Anderson OR (1988a) Comparative Protozoology: Ecology, Physiology, Life History. Heidelberg, Germany: Springer‐Verlag.

Anderson OR (1988b) Fine structure of silica deposition and origin of shell components in the testate amoeba Netzelia tuberculata. Journal of Protozoology 35: 204–211.

Anderson OR (1992) A fine structural study of Physarum polycephalum during transformation from sclerotium to plasmodium: a six stage description. Journal of Protozoology 30: 213–223.

Baverstock PR, Illana S, Christy PE, Robinson BS and Johnson AM (1989) srRNA evolution and phylogenetic relationships of the genus Naegleria (Protista: Rhizopoda). Molecular Biology and Evolution 6: 243–257.

Brown S and De Jonckheere JF (1994) Identification and phylogenetic relationships of Vahlkampfia spp. (free‐living amoebae) by riboprinting. FEMS Microbiology Letters 115: 241–246.

Burki F and Pawlowski J (2006) Monophyly of Rhizaria and multigene phylogeny of unicellular bikonts. Molecular Biology and Evolution 23: 1922–1930.

Cavalier‐Smith T (1998) A revised six‐kingdom system of life. Biological Review 73: 203–266.

Cavalier‐Smith T and Chao EE (1996) Sarcomonad ribosomal RNA sequences, rhizopod phylogeny, and the origin of euglyphid amoebae. Archiv für Protistenkunde 147: 227–236.

Fiore‐Donno AM, Nikolaev S, Nelson M et al. (2010) Deep phylogeny and evolution of slime moulds (Mycetozoa). Protist 161: 55–70.

Hemleben C, Spindler M and Anderson OR (1989) Modern Planktonic Foraminifera. New York: Springer‐Verlag.

Hinkle G and Sogin ML (1993) The evolution of the Vahlkampfiidae as deduced from 16S‐like ribosomal RNA analysis. Journal of Eukaryotic Microbiology 40: 599–603.

Lee JJ and Anderson OR (eds) (1991) Biology of Foraminifera. London: Academic Press.

Lee JJ, Hutner SH and Bovee EC (eds) (1985) Illustrated Guide to the Protozoa. Lawrence, KS: Society of Protozoologists.

Lee JJ, Leedale GF and Bradbury P (2000) The Illustrated Guide to the Protozoa, 2nd edn. Lawrence, KS: Society of Protozoologists.

Levine ND, Corliss JO, Cox FEG et al. (1980) A newly revised classification of the Protozoa. Journal of Protozoology 27: 37–59.

Margulis L, Corliss JO, Melkonian M and Chapman DJ (eds) (1990) Handbook of Protoctista. Boston, MA: Jones and Bartlett Publishers.

Minge MA, Silberman JD, Orr RJS et al. (2009) Evolutionary position of breviate amoebae and the primary eukaryote divergence. Proceedings of the Royal Society B: Biological Sciences 27: 597–604.

Nikolaev SI, Berney C, Fahrni JF et al. (2004) The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes. Proceedings of the National Academy of Sciences of the United States of America 101: 8066–8071.

Ogden C and Hedley RH (1980) An Atlas of Freshwater Testate Amoebae. Oxford: Oxford University Press.

Page FC (1988) A New Key to Freshwater and Soil Gymnamoebae. Ambleside, UK: Freshwater Biological Association.

Patterson DJ (1994) Protozoa: evolution and systematics. In: Hausmann K and Hülsmann N (eds) Progress in Protozoology, pp. 1–14. Stuttgart, Germany: Gustav Fischer‐Verlag.

Pawlowski J and Burki F (2009) Untangling the phylogeny of amoeboid protists. Journal of Eukaryotic Microbiology 56: 16–25.

Pawlowski J, Bolivar I, Fahrni JF, Cavalier‐Smith T and Gouy M (1996) Early origin of foraminifera suggested by SSU rRNA gene sequences. Molecular Biology and Evolution 13: 445–450.

Rogozin IB, Basu MK, Csueroes M and Koonin EV (2009) Analysis of rare genomic changes does not support the unikont–bikont phylogeny and suggests cyanobacterial symbiosis as the point of primary radiation of eukaryotes. Genome Biology and Evolution 1: 99–113.

Shadwick LL, Spiegel FW, Shadwick JDL, Brown MW and Silberman JD (2009) Eumycetozoa=Amoebozoa?: SSUrDNA phlogeny of protosteloid slime molds and its significance for the amoebozoan supergroup. PloS One 4: e6754.

Silberman JD, Clark CG, Diamond LS and Sogin ML (1999) Phylogeny of the genera Entamoeba and Endolimax as deduced from small‐subunit ribosomal RNA sequences. Molecular Biology and Evolution 16: 1740–1751.

Sims GP, Rogerson A and Aitken R (1999) Primary and secondary structure of the small‐subunit ribosomal RNA of the naked, marine amoeba Vannella anglica: phylogenetic implications. Journal of Molecular Evolution 48: 740–749.

Sleigh M (1989) Protozoa and Other Protists. London: Edward Arnold.

Smirnov AV, Nassonova E, Berney C et al. (2005) Molecular phylogeny and classification of the lobose amoebae. Protist 156: 129–142.

Tappan H and Loeblich AR Jr (1988) Foraminiferal evolution, diversification, and extinction. Journal of Paleontology 62: 695–714.

Further Reading

Darbyshire JF (ed.) (1994) Soil Protozoa. Wallingford, UK: CAB International.

Laybourn‐Parry J (1992) Protozoan Plankton Ecology. London: Chapman & Hall.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

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