Amoebae: Protists Which Move and Feed Using Pseudopodia

David J. Patterson

The amoeboid body form is one of the most widespread. Not only does it occur in amoebae, but it is also found in algae, fungi and animals. From comparisons of molecular data and from life history data, it is clear that the amoeboid body form is an adaptive form and that the amoebae are polyphyletic.

Traditionally, the amoebae have been classified as the protozoan taxon Sarcodina, with a taxonomic structure that separated species with supported pseudodpodia from those with unsupported pseudopodia, and those with skeletal elements, from those without. Older schemes such as this grouped together related taxa and exluded other related taxa. The amoebae are probably the last large area of protists which have to be fully documented and explored, although progress in that area is now taking place (Amaral, Silberman).

The "Sarcodina" included the following taxa:

The amoebae are of importance both medically and ecologically. Naegleria is the cause of amoebic meningitis; other species are more or less benign coresidents in digestive systems of ourselves or other animals or can facultatively attack the conjunctiva of our eyes. In marine ecosystems, radiolaria and foraminifera are significant members of communities, both as consumers and as producers (many planktonic marine amoebae and foraminifera from intertidal habitats harbour large numbers of symbiotic algae). Naked amoebae are major consumers of bacteria in soil ecosystems and are believed to occupy the same key role there as flagellates do in aquatic ecosystems (that of recycling bacterial productivity and ensuring nutrient regeneration and continued functioning of the ecosystem).

Click on an image to view larger version & data in a new window
Click on an image to view larger version & data in a new window

Mayorella (Gymnamoebae) a naked amoeba with conical pseudopodia, living cell.

Amoebae are frequently maligned as shapeless blobs. Despite their evident pleomorphism which comes from being able to emit and resorb extensions of cytoplasm, active amoebae do have a front and a back.

Pseudopodia. Different categories of amoebae can be distinguished by the appearance of the pseudopodia, and these are summarised in the diagram below. Pseudopodia may have internal microtubules which give them rigidity (as in radiolaria, heliozoa and foraminifera). The stiffened pseudopodia of radiolaria and heliozoa tend to extend radially and are called actinopoda. Those of foraminifera branch and fuse, and because of the resulting net-like structure, are referred to as granulo-reticulose pseudopodia. Unsupported pseudopodia may be lobose (broad) or filose (thread-like), many may be produced at the same time (polypodial) or cells may migrate with a single advancing pseudopodium (monopodial).

Click on an image to view larger version & data in a new window
Click on an image to view larger version & data in a new window
The forms of pseudopodia

The forms of pseudopodia: from left: polypodial and lobose, monopodial and lobose, filose, conical, granuloreticulose, tapering actinopods, non-tapering actinopods.

The posterior end of lobose amoebae may also be distinctive, and is referred to as the uroid. The form of this region may be distinctive.

Ultrastructure. As with other protists, details of nuclear division profiles, mitochondria, extrusomes and other inclusions have helped to establish the identities for categories of amoebae - especially the heliozoa and radiolaria. The ramicristates are a major subset of amoeboid organisms distinguished by having branched cristae within the mitochondria.

Life cycle: amoebae typically grow and divide; this pattern of vegetative growth may or may not include encysted states, flagellated forms, or a transition from a sexual to an asexual phase of growth.

The amoeboid body form is widespread among the protists. The following groups are entirely or predominantly amoeboid - except where specified.

Groups of Heterotrophic Amoebae

Name of group Organization Composition / sample genera
Acantharea radiolaria Very diverse, e.g. Acanthometron
Biomyxa Named amoebae with thin anastomosing pseuodopodia One genus
Centroheliozoa heliozoa About 10 genera, e.g. Acanthocystis, Heterophrys, Raphidocystis
Copromyxids slime mould 2 genera
Desmothoracids heliozoon-like e.g. Clathrulina
Entamoebidae amoebae, mitochondria absent A few genera only, e.g. Entamoeba
Excavates mostly flagellates, but amoeboid and slime mould organisms occur within the Heterolobosea e.g. Naegleria, Acrasis (acrasid slime moulds)
Fonticula slime-mould Isolated genus
Granuloreticulosa amoebae with thin, stiff and anastomosing pseudopodia, most (Foraminifera) with a single or many chambered shell. Very diverse, with a substantial fossil record, e.g. Reticulomyxa, Lagena, Globigerina, Elphidium.
Gymnophrea several genera of amoebae, thin pseudopodia, with short inactive flagellar stumps Gymnophrys, Barkowia
Gymnosphaerida a type of heliozoon Gymnosphaera, Hedraiophrys, Actinocoryne
Komokiacea very large marine amoebae About 12 genera
Nucleariidae with thin unbranching pseudopodia Nuclearia, Vampyrellidium, Pinaciophora, Pompholyxophrys, Rabdiophrys
Pelobionts several genera of amitochondriate flagellates, but one genus is often considered as an amoeba Pelomyxa
Phaeodarea a type of radiolaria, common About 100 genera
Polycystinea a type of radiolaria, common Diverse
Ramicristates this group contains most of the non-actinopod amoebae Naked amoebae, testate amoebae, dictyostelid and myxomycete slime moulds, diverse, e.g. Hyperamoeba, Gromia, Acanthamoeba
Sticholonche genus of heliozoa with mobile arms Single genus, two species
Vampyrellids fungus- and alga-eating amoebae e.g. Vampyrella
Xenophyophores large marine amoebae About 15 genera, 50 species

Genera of amoebae for which no clear identity has been developed (after Patterson, 1999):

  • Actinocoma
  • Actinolophus
  • Aletium
  • Actinastrum
  • Actinelius
  • Amphitrema
  • Apogromia
  • Asterocaelum
  • Astrolophus
  • Belaria
  • Belonocystis
  • Branchipocola
  • Chlamydophrys
  • Chlamydomyxa
  • Cichkovia
  • Cinetidomyxa
  • Clathrella
  • Dictyomyxa
  • Dinamoeba
  • Dobellina
  • Elaerorhanis
  • Endamoeba
  • Endalimax
  • Enteromyxa
  • Flamella
  • Gymnophrydium
  • Hartmannina
  • Heterogromia
  • Hyalodaktylethra
  • Iodamoeba
  • Janickina
  • Kibisidytes
  • Lagenidiopsis
  • Leptophrys
  • Liegeosia
  • Lithocolla
  • Malpighiella
  • Martineziella
  • Megamoebamyxa
  • Microgromia
  • Myxodictyum
  • Penardia
  • Pleurophrys
  • Podactinelius
  • Podostoma
  • Pontomyxa
  • Protogenes
  • Protomonas
  • Raphidiophryopsis
  • Reticulamoeba
  • Rhizoplasma
  • Servetia
  • Stygamoeba
  • Thalassomyxa
  • Theratromyxa
  • Topsentella
  • Trizona
  • Urbanella
  • Wagnerella


Cavalier-Smith, T. 1993. Kingdom Protozoa and its 18 phyla. Microbiol. Rev. 57:953-94.

Copeland, H. F. 1956. Classification of the Lower Organisms. Pacific Books, Palo Alto, California.

Corliss, J. O. 1984. The Kingdom Protista and its 45 phyla. BioSystems 17: 87-126.

Margulis L., Corliss J. O., Melkonian, M. and Chapman D. J. 1990. Handbook of Protoctista. Jones and Bartlett Publishers, Boston.

Patterson, D. J. 1999. The diversity of eukaryotes. Am. Nat. 154 (suppl.):S96-S124.

About This Page

David J. Patterson
Marine Biological Laboratory, Woods Hole, Massachusetts, USA

Page: Tree of Life Amoebae: Protists Which Move and Feed Using Pseudopodia Authored by David J. Patterson. The TEXT of this page is licensed under the Creative Commons Attribution License - Version 3.0. Note that images and other media featured on this page are each governed by their own license, and they may or may not be available for reuse. Click on an image or a media link to access the media data window, which provides the relevant licensing information. For the general terms and conditions of ToL material reuse and redistribution, please see the Tree of Life Copyright Policies.

close box

This page is a note that is attached to a branch of the Tree of Life.

ToL notes provide brief accounts of characteristics, short summaries, commentaries, media files, taxonomic information, or identification tools for a given group of organisms.

For a more detailed explanation of the different ToL page types, have a look at the Structure of the Tree of Life page.

close box


Page Content

articles & notes




Explore Other Groups

random page

  go to the Tree of Life home page