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An amoeba (; less commonly spelled ameba or amœba; : amoebas (less commonly, amebas) or amoebae (amebae) ), often called an amoeboid, is a type of cell or
unicellular organism A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...
with the ability to alter its shape, primarily by extending and retracting pseudopods. Amoebae do not form a single taxonomic group; instead, they are found in every major lineage of
eukaryotic The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
organisms. Amoeboid cells occur not only among the
protozoa Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically ...
, but also in
fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
,
algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...
, and
animals Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia (). With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a ...
.
Microbiologist A microbiologist (from Greek ) is a scientist who studies microscopic life forms and processes. This includes study of the growth, interactions and characteristics of microscopic organisms such as bacteria, algae, fungi, and some types of par ...
s often use the terms "amoeboid" and "amoeba" interchangeably for any organism that exhibits
amoeboid movement Amoeboid movement is the most typical mode of locomotion in adherent eukaryotic cells. It is a crawling-like type of movement accomplished by protrusion of cytoplasm of the cell involving the formation of pseudopodia ("false-feet") and posterio ...
. In older classification systems, most amoebae were placed in the
class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...
or
subphylum In zoological nomenclature, a subphylum is a taxonomic rank below the rank of phylum. The taxonomic rank of " subdivision" in fungi and plant taxonomy is equivalent to "subphylum" in zoological taxonomy. Some plant taxonomists have also used th ...
Sarcodina, a grouping of single-celled organisms that possess pseudopods or move by
protoplasm Protoplasm (; ) is the part of a cell that is surrounded by a plasma membrane. It is a mixture of small molecules such as ions, monosaccharides, amino acids, and macromolecules such as proteins, polysaccharides, lipids, etc. In some definitions ...
ic flow. However,
molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
studies have shown that Sarcodina is not a
monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...
group whose members share
common descent Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. According to modern evolutionary biology, all living beings could be descendants of a unique ancestor commonl ...
. Consequently, amoeboid organisms are no longer classified together in one group. The best known amoeboid
protists A protist ( ) or protoctist is any Eukaryote, eukaryotic organism that is not an animal, Embryophyte, land plant, or fungus. Protists do not form a Clade, natural group, or clade, but are a Paraphyly, paraphyletic grouping of all descendants o ...
are ''
Chaos carolinense ''Chaos'' is a genus of single-celled amoeboid organisms in the family Amoebidae. The largest and most-known species, the so-called "giant amoeba" (''Chaos carolinensis''), can reach lengths up to 5 mm, although most specimens fall betwee ...
'' and ''
Amoeba proteus ''Amoeba proteus'' is a large species of amoeba closely related to another genus of giant amoebae, ''Chaos (genus), Chaos''. As such, the species is sometimes given the alternative scientific name ''Chaos diffluens''. This protozoan uses extensi ...
'', both of which have been widely cultivated and studied in classrooms and laboratories. Other well known species include the so-called "brain-eating amoeba" ''
Naegleria fowleri ''Naegleria fowleri'', also known as the brain-eating amoeba, is a species of the genus ''Naegleria''. It belongs to the phylum Percolozoa and is classified as an amoeboflagellate Excavata, excavate, an organism capable of behaving as both an ...
'', the intestinal parasite ''
Entamoeba histolytica ''Entamoeba histolytica'' is an anaerobic organism, anaerobic parasitic amoebozoan, part of the genus ''Entamoeba''. Predominantly infecting humans and other primates causing amoebiasis, ''E. histolytica'' is estimated to infect about 35-50 mil ...
'', which causes
amoebic dysentery Amoebiasis, or amoebic dysentery, is an infection of the intestines caused by a parasitic amoeba '' Entamoeba histolytica''. Amoebiasis can be present with no, mild, or severe symptoms. Symptoms may include lethargy, loss of weight, coloni ...
, and the multicellular "social amoeba" or
slime mould Slime mold or slime mould is an informal name given to a polyphyletic assemblage of unrelated eukaryotic organisms in the Stramenopiles, Rhizaria, Discoba, Amoebozoa and Holomycota clades. Most are near-microscopic; those in the Myxogastria ...
''
Dictyostelium discoideum ''Dictyostelium discoideum'' is a species of soil-dwelling Amoeboid, amoeba belonging to the phylum Amoebozoa, infraphylum Mycetozoa. Commonly referred to as slime mold, ''D. discoideum'' is a eukaryote that transitions from a collection of unic ...
''.


Biology


Pseudopods and movement

Amoebae do not have cell walls, which allows for free movement. Amoebae move and feed by using pseudopods, which are bulges of
cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...
formed by the coordinated action of
actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of ...
microfilaments Microfilaments, also called actin filaments, are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton. They are primarily composed of polymers of actin, but are modified by and interact with numerous other p ...
pushing out the
plasma membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...
that surrounds the cell. The appearance and internal structure of pseudopods are used to distinguish groups of amoebae from one another. Amoebozoan species, such as those in the genus ''
Amoeba An amoeba (; less commonly spelled ameba or amœba; : amoebas (less commonly, amebas) or amoebae (amebae) ), often called an amoeboid, is a type of Cell (biology), cell or unicellular organism with the ability to alter its shape, primarily by ...
'', typically have bulbous (lobose) pseudopods, rounded at the ends and roughly tubular in cross-section. Cercozoan amoeboids, such as ''
Euglypha ''Euglypha'' is a genus of cercozoa. It includes the species ''Euglypha rotunda''. References External links

* * Imbricatea Rhizaria genera {{Cercozoa-stub ...
'' and ''
Gromia ''Gromia'' is a genus of protists, closely related to foraminifera, which inhabit marine and freshwater environments. It is the only genus of the family Gromiidae. ''Gromia'' are ameboid, producing filose pseudopodia that extend out from the cel ...
'', have slender, thread-like (filose) pseudopods.
Foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...
emit fine, branching pseudopods that merge with one another to form net-like (reticulose) structures. Some groups, such as the
Radiolaria The Radiolaria, also called Radiozoa, are unicellular eukaryotes of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ect ...
and
Heliozoa Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (Pseudopodia#Morphology, axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule- ...
, have stiff, needle-like, radiating
axopodia A pseudopod or pseudopodium (: pseudopods or pseudopodia) is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filaments and ...
(actinopoda) supported from within by bundles of
microtubules Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27  nm and have an inner diameter between 11 an ...
. Free-living amoebae may be "
testate Intestacy is the condition of the estate of a person who dies without a legally valid will, resulting in the distribution of their estate under statutory intestacy laws rather than by their expressed wishes. Alternatively this may also apply ...
" (enclosed within a hard shell), or "naked" (also known as gymnamoebae, lacking any hard covering). The shells of testate amoebae may be composed of various substances, including
calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
,
silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...
,
chitin Chitin (carbon, C8hydrogen, H13oxygen, O5nitrogen, N)n ( ) is a long-chain polymer of N-Acetylglucosamine, ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cell ...
, or agglutinations of found materials like small grains of sand and the frustules of
diatoms A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...
. To regulate
osmotic pressure Osmotic pressure is the minimum pressure which needs to be applied to a Solution (chemistry), solution to prevent the inward flow of its pure solvent across a semipermeable membrane. It is also defined as the measure of the tendency of a soluti ...
, most freshwater amoebae have a contractile
vacuole A vacuole () is a membrane-bound organelle which is present in Plant cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...
which expels excess water from the cell. This
organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as Organ (anatomy), organs are to th ...
is necessary because freshwater has a lower concentration of
solutes In chemistry, a solution is defined by IUPAC as "A liquid or solid phase containing more than one substance, when for convenience one (or more) substance, which is called the solvent, is treated differently from the other substances, which are ...
(such as salt) than the amoeba's own internal fluids (
cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...
). Because the surrounding water is
hypotonic In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective memb ...
with respect to the contents of the cell, water is transferred across the amoeba's cell membrane by
osmosis Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively permeable membrane, selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of ...
. Without a contractile vacuole, the cell would fill with excess water and, eventually, burst. Marine amoebae do not usually possess a contractile vacuole because the concentration of solutes within the cell are in balance with the
tonicity In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two Solution (chemistry), solutions separated by a Semipermeable membrane, partially-permeable cell Cell membrane, membrane. Tonicity ...
of the surrounding water.


Nutrition

The food sources of amoebae vary. Some amoebae are predatory and live by consuming bacteria and other
protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...
s. Some are
detritivore Detritivores (also known as detrivores, detritophages, detritus feeders or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrates, ...
s and eat dead organic material. Amoebae typically ingest their food by
phagocytosis Phagocytosis () is the process by which a cell (biology), cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs ph ...
, extending pseudopods to encircle and engulf live prey or particles of scavenged material. Amoeboid cells do not have a mouth or
cytostome A cytostome (from ''cyto-'', cell and ''stome-'', mouth) or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacu ...
, and there is no fixed place on the cell at which phagocytosis normally occurs. Some amoebae also feed by
pinocytosis In cellular biology, pinocytosis, otherwise known as fluid endocytosis and bulk-phase pinocytosis, is a mode of endocytosis in which small molecules dissolved in extracellular fluid are brought into the cell through an invagination of the cell me ...
, imbibing dissolved nutrients through vesicles formed within the cell membrane.


Size range

The size of amoeboid cells and species is extremely variable. The marine amoeboid '' Massisteria voersi'' is just 2.3 to 3
micrometre The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...
s in diameter, within the size range of many bacteria. At the other extreme, the shells of deep-sea xenophyophores can attain 20 cm in diameter. Most of the free-living freshwater amoebae commonly found in pond water, ditches, and lakes are
microscopic The microscopic scale () is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens or microscope to see them clearly. In physics, the microscopic scale is sometimes regarded as the scale betwe ...
, but some species, such as the so-called "giant amoebae" ''Pelomyxa palustris'' and ''Chaos carolinense'', can be large enough to see with the naked eye.


Sexual reproduction

Recent evidence indicates that several Amoebozoa lineages undergo
meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...
.
Orthologs Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a spec ...
of genes employed in
meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...
of sexual
eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
s have recently been identified in the ''
Acanthamoeba ''Acanthamoeba'' is a genus of amoeboid, amoebae that are commonly recovered from soil, fresh water, and other habitat (ecology), habitats. The genus ''Acanthamoeba'' has two stages in its life cycle, the metabolically active trophozoite stage a ...
''
genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...
. These genes included ''
Spo11 Spo11 is a protein that in humans is encoded by the ''SPO11'' gene. Spo11, in a complex with mTopVIB, creates double strand breaks to initiate meiotic recombination. Its active site contains a tyrosine which ligates and dissociates with DNA to p ...
, Mre11,
Rad50 DNA repair protein RAD50, also known as RAD50, is a protein that in humans is encoded by the ''RAD50'' gene. Function The protein encoded by this gene is highly similar to ''Saccharomyces cerevisiae'' Rad50, a protein involved in DNA double- ...
,
Rad51 DNA repair protein RAD51 homolog 1 is a protein encoded by the gene ''RAD51''. The enzyme encoded by this gene is a member of the RAD51 protein family which assists in repair of DNA double strand breaks. RAD51 family members are homologous to t ...
, Rad52, Mnd1, Dmc1, Msh'' and '' Mlh''. This finding suggests that the ‘'Acanthamoeba'’ are capable of some form of meiosis and may be able to undergo sexual reproduction. The meiosis-specific
recombinase Recombinases are genetic recombination enzymes. Site specific recombinases DNA recombinases are widely used in multicellular organisms to manipulate the structure of genomes, and to control gene expression. These enzymes, derived from bacteria ( ...
, Dmc1, is required for efficient meiotic
homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in Cell (biology), cellular organi ...
, and ''Dmc1'' is expressed in ''
Entamoeba histolytica ''Entamoeba histolytica'' is an anaerobic organism, anaerobic parasitic amoebozoan, part of the genus ''Entamoeba''. Predominantly infecting humans and other primates causing amoebiasis, ''E. histolytica'' is estimated to infect about 35-50 mil ...
''. The purified Dmc1 from ''E. histolytica'' forms
presynaptic In the nervous system, a synapse is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending o ...
filaments and catalyses ATP-dependent homologous DNA pairing and DNA strand exchange over at least several thousand
base pairs A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...
. The DNA pairing and strand exchange reactions are enhanced by the eukaryotic meiosis-specific recombination accessory factor (heterodimer) Hop2-Mnd1. These processes are central to meiotic recombination, suggesting that ''E. histolytica'' undergoes meiosis. Studies of '' Entamoeba invadens'' found that, during the conversion from the
tetraploid Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...
uninucleate trophozoite to the tetranucleate cyst,
homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in Cell (biology), cellular organi ...
is enhanced. Expression of genes with functions related to the major steps of meiotic recombination also increase during encystations. These findings in ''E. invadens'', combined with evidence from studies of ''E. histolytica'' indicate the presence of meiosis in the ''Entamoeba''. ''
Dictyostelium discoideum ''Dictyostelium discoideum'' is a species of soil-dwelling Amoeboid, amoeba belonging to the phylum Amoebozoa, infraphylum Mycetozoa. Commonly referred to as slime mold, ''D. discoideum'' is a eukaryote that transitions from a collection of unic ...
'' in the supergroup
Amoebozoa Amoebozoa is a major Taxonomy (biology), taxonomic group containing about 2,400 described species of Amoeba, amoeboid protists, often possessing blunt, fingerlike, Pseudopod#Morphology, lobose pseudopods and tubular mitochondrial cristae. In trad ...
can undergo mating and
sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...
including meiosis when food is scarce. Since the Amoebozoa diverged early from the
eukaryotic The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
family tree, these results suggest that meiosis was present early in eukaryotic evolution. Furthermore, these findings are consistent with the proposal of Lahr et al. that the majority of amoeboid lineages are anciently sexual.


Ecology


Pathogenic amoebae

Some amoebae can infect other organisms
pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...
ically, causing disease: *''
Entamoeba histolytica ''Entamoeba histolytica'' is an anaerobic organism, anaerobic parasitic amoebozoan, part of the genus ''Entamoeba''. Predominantly infecting humans and other primates causing amoebiasis, ''E. histolytica'' is estimated to infect about 35-50 mil ...
'' is the cause of
amoebiasis Amoebiasis, or amoebic dysentery, is an infection of the intestines caused by a parasitic amoeba '' Entamoeba histolytica''. Amoebiasis can be present with no, mild, or severe symptoms. Symptoms may include lethargy, loss of weight, colon ...
, or amoebic dysentery. *''
Naegleria fowleri ''Naegleria fowleri'', also known as the brain-eating amoeba, is a species of the genus ''Naegleria''. It belongs to the phylum Percolozoa and is classified as an amoeboflagellate Excavata, excavate, an organism capable of behaving as both an ...
'' (the "brain-eating amoeba") is a fresh-water-native species that can be fatal to humans if introduced through the nose. *''
Acanthamoeba ''Acanthamoeba'' is a genus of amoeboid, amoebae that are commonly recovered from soil, fresh water, and other habitat (ecology), habitats. The genus ''Acanthamoeba'' has two stages in its life cycle, the metabolically active trophozoite stage a ...
'' can cause amoebic
keratitis Keratitis is a condition in which the human eye, eye's cornea, the clear dome on the front surface of the eye, becomes inflammation, inflamed. The condition is often marked by moderate to intense pain and usually involves any of the following sy ...
and
encephalitis Encephalitis is inflammation of the Human brain, brain. The severity can be variable with symptoms including reduction or alteration in consciousness, aphasia, headache, fever, confusion, a stiff neck, and vomiting. Complications may include se ...
in humans. *'' Balamuthia mandrillaris'' is the cause of (often fatal) granulomatous amoebic meningoencephalitis. Amoebae have been found to harvest and grow the bacteria implicated in plague. Amoebae can likewise play host to microscopic organisms that are pathogenic to people and help in spreading such microbes. Bacterial pathogens (for example, ''
Legionella ''Legionella'' is a genus of gram-negative bacteria, gram-negative bacteria that can be seen using a silver stain or grown in a special media that contains cysteine, an amino acid. It is known to cause legionellosis (all illnesses caused by ''Legi ...
'') can oppose absorption of food when devoured by amoebae. The currently generally utilized and best-explored amoebae that host other organisms are Acanthamoeba castellanii and Dictyostelium discoideum. Microorganisms that can overcome the defenses of one-celled organisms can shelter and multiply inside them, where they are shielded from unfriendly outside conditions by their hosts.


History of knowledge and classification


Conceptual origins

The earliest record of an amoeboid organism was produced in 1755 by
August Johann Rösel von Rosenhof August Johann Rösel von Rosenhof (March 30, 1705 in Augustenburg, Germany, Augustenburg near Arnstadt – March 27, 1759 in Nuremberg) was a German Miniature (illuminated manuscript), miniature painter, natural history, naturalist and entom ...
, who named his discovery "Der Kleine Proteus" ("the Little Proteus"). Rösel's illustrations show an unidentifiable freshwater amoeba, similar in appearance to the common species now known as ''
Amoeba proteus ''Amoeba proteus'' is a large species of amoeba closely related to another genus of giant amoebae, ''Chaos (genus), Chaos''. As such, the species is sometimes given the alternative scientific name ''Chaos diffluens''. This protozoan uses extensi ...
''. The term "Proteus animalcule" remained in use throughout the 18th and 19th centuries, as an informal name for any large, free-living amoeboid. In 1822, the genus ''Amiba'' (from the
Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...
ἀμοιβή ''amoibe'', meaning "change") was erected by the French naturalist
Bory de Saint-Vincent Jean-Baptiste Geneviève Marcellin Bory de Saint-Vincent was a French naturalist, officer and politician. He was born on 6 July 1778 in Agen (Lot-et-Garonne) and died on 22 December 1846 in Paris. Biologist and geographer, he was particularly int ...
. Bory's contemporary, C. G. Ehrenberg, adopted the genus in his own classification of microscopic creatures, but changed the spelling to ''Amoeba''. In 1841, Félix Dujardin coined the term "''sarcode''" (from Greek σάρξ ''sarx'', "flesh", and εἶδος ''eidos'', "form") for the "thick, glutinous, homogeneous substance" which fills protozoan cell bodies. Although the term originally referred to the protoplasm of any protozoan, it soon came to be used in a restricted sense to designate the gelatinous contents of amoeboid cells. Thirty years later, the Austrian zoologist Ludwig Karl Schmarda used "sarcode" as the conceptual basis for his division Sarcodea, a
phylum In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...
-level group made up of "unstable, changeable" organisms with bodies largely composed of "sarcode". Later workers, including the influential taxonomist
Otto Bütschli Johann Adam Otto Bütschli (3 May 1848 – 2 February 1920) was a German zoologist and professor at the University of Heidelberg. He specialized in invertebrates and insect development. Many of the groups of protists were first recognized by him. ...
, amended this group to create the class Sarcodina, a
taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
that remained in wide use throughout most of the 20th century.


Traditional classification

For convenience, all amoebae were grouped as Sarcodina and generally divided into morphological categories, on the basis of the form and structure of their
pseudopod A pseudopod or pseudopodium (: pseudopods or pseudopodia) is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filaments and ...
s. Amoebae with pseudopods supported by regular arrays of
microtubule Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...
s (such as the freshwater
Heliozoa Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (Pseudopodia#Morphology, axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule- ...
and marine
Radiolaria The Radiolaria, also called Radiozoa, are unicellular eukaryotes of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ect ...
) were classified as Actinopoda, whereas those with unsupported pseudopods were classified as Rhizopoda. The Rhizopods were further subdivided into lobose, filose, plasmodial and reticulose, according to the morphology of their pseudopods. During the 1980s, taxonomists reached the following classification, based exclusively on morphological comparisons: * Sarcodina : all amoebae. :*Rhizopoda : amorphous amoebae that lack axopodia and move through pseudopodia. ::* Heterolobosea : amoebae with eruptive pseudopodia, similar to the lobose ones but with a distinct movement, and usually with flagellate life stages. It was traditionally divided into those which aggregate to form fruiting bodies ( Acrasida) and those that do not ( Schizopyrenida). ::* Lobosea : amoebae with lobose pseudopodia. This
paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
group is now represented by a big portion of the current phylum
Amoebozoa Amoebozoa is a major Taxonomy (biology), taxonomic group containing about 2,400 described species of Amoeba, amoeboid protists, often possessing blunt, fingerlike, Pseudopod#Morphology, lobose pseudopods and tubular mitochondrial cristae. In trad ...
, in particular the classes
Tubulinea The Tubulinea are a major grouping of Amoebozoa, including most of the more familiar amoebae genera like ''Amoeba'', '' Arcella'', '' Difflugia'' and '' Hartmannella''. Characteristics During locomotion most Tubulinea have a roughly cylindrica ...
,
Discosea Discosea is a class of Amoebozoa, consisting of naked amoebae with a flattened, discoid body shape. Members of the group do not produce tubular or subcylindrical pseudopodia, like amoebae of the class Tubulinea. When a discosean is in motion, a ...
and
Cutosea Cutosea () is a small group of marine amoeboid protists proposed in 2016. It is a monotypic class of Amoebozoa containing the order Squamocutida (). Cutosean organisms are characterized by a cell coat of microscales separated from the cell membr ...
. :::*Gymnamoebia : lobose naked amoebae. This
polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...
group included the classic amorphous amoebae with big, blunt pseudopodia, such as Euamoebida,
Leptomyxida Leptomyxida is an order of Amoebozoa. It includes species such as ''Flabellula citata'', ''Paraflabellula hoguae'', ''Paraflabellula reniformis'', ''Rhizamoeba saxonica'' and ''Leptomyxa reticulata''. Taxonomy The taxonomy of Leptomyxida as rev ...
, Acanthopodida, Echinamoebida, Entamoebida, etc. :::*Testacealobosia : lobose
testate amoebae Testate amoebae (formerly thecamoebians, Testacea or Thecamoeba) are a polyphyletic group of unicellular amoeboid protists, which differ from naked amoebae in the presence of a test (biology), test that partially encloses the cell, with an apert ...
. This polyphyletic group included three unrelated lineages of amoebozoans enclosed by tests or other complex coverings: Arcellinida, Himatismenida and Trichosida. ::* Caryoblastea : amoebae with sparse, non-motile flagella on the surface. This group only includes the order
Pelobiontida The Archamoebae are a group of protists originally thought to have evolved before the acquisition of mitochondria by eukaryotes. They include genera that are internal parasites or commensals of animals ('' Entamoeba'' and '' Endolimax''). A few ...
, which now belongs to the amoebozoan group Archamoebae together with some naked amoebae. ::* Eumycetozoea : plasmodial amoebae with filiform subpseudopodia that produce fruiting bodies. ::* Plasmodiophorea : endoparasitic plasmodial amoebae with minute pseudopodia. This group is now an order within
Rhizaria The Rhizaria are a diverse and species-rich clade of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus '' Paulinella'' in the phylum Cercozoa, they are all non-photosynthetic, but many Foraminifera ...
, closely related to the endoparasites Phagomyxida. ::* Filosea : amoebae with filose pseudopodia. :::*Aconchulinia : filose naked amoebae, sometimes covered in scales. This group included two unrelated taxa: the
nucleariid The nucleariids, or nucleariid amoebae, are a group of amoebae that compose the sister clade of the fungi. Together, they form the clade Holomycota. They are aquatic organisms found in freshwater and marine habitats, as well as in faeces. They ...
amoebae, closely related to
fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
; and most of the Vampyrellida, found in Rhizaria. :::*Testaceafilosia : filose testate amoebae. This group included taxa now found throughout Rhizaria, such as
Gromiida Gromiida is an order of Endomyxa. It is the only order in the class Gromiidea. Taxonomy Class Gromiidea Cavalier-Smith 2003 sensu Bass et al. 2009 * Order Gromiida Claparède & Lachmann 1856 s.s. ** Family Gromiidae Ruess 1862 romiina Delage ...
and Euglyphida. ::*Granuloreticulosea : amoebae with delicate granular pseudopodia. This group included both the
Foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...
(now in Rhizaria) and some members of Vampyrellida. ::*
Xenophyophorea Xenophyophorea is a clade of foraminiferans. Xenophyophores are multinucleate unicellular organisms found on the ocean floor throughout the world's oceans, at depths of . They are a kind of foraminiferan that extract minerals from their surround ...
: plasmodial amoebae enclosed in a branched-tube system composed of a transparent organic substance. This group is now fully integrated into the Foraminifera. :*Actinopoda : spherical amoebae that float in the water column. This group included those organisms that have a
heliozoa Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (Pseudopodia#Morphology, axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule- ...
n-type appearance, with radially positioned filopodia, reticulopodia or axopodia surrounding the cell body. These were the
Radiolaria The Radiolaria, also called Radiozoa, are unicellular eukaryotes of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ect ...
,
Phaeodaria Phaeodarea or Phaeodaria is a group of amoeboid cercozoan organisms. They are traditionally considered radiolarians, but in molecular trees do not appear to be close relatives of the other groups, and are instead placed among the Cercozoa. They a ...
, Proteomyxidea (all three now in Rhizaria), Centroplasthelida (now in
Haptista Haptista is a proposed group of protists made up of centrohelids and haptophytes. Phylogenomic studies indicate that Haptista, together with ''Ancoracysta twista'', forms a sister clade to the SAR supergroup#Internal phylogeny, TSAR Supergroup (b ...
), and
Actinophryida The actinophryids are an order of heliozoa, a polyphyletic array of stramenopiles, having a close relationship with pedinellids and ''Ciliophrys''. They are common in fresh water and occasionally found in marine and soil habitats. Actinophryids a ...
(now in
Stramenopiles The stramenopiles, also called heterokonts, are Protist, protists distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular sur ...
).


Transitional period

In the final decades of the 20th century, a series of molecular phylogenetic analyses confirmed that Sarcodina was not a
monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...
group, and that amoebae evolved from flagellate ancestors. The protozoologist
Thomas Cavalier-Smith Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 – 19 March 2021), was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford. His research has led to discov ...
proposed that the ancestor of most eukaryotes was an amoeboflagellate much like modern heteroloboseans, which in turn gave rise to a paraphyletic Sarcodina from which other groups (e.g., alveolates, animals, plants) evolved by a secondary loss of the amoeboid phase. In his scheme, the Sarcodina were divided into the more primitive Eosarcodina (with the phyla Reticulosa and Mycetozoa) and the more derived Neosarcodina (with the phyla
Amoebozoa Amoebozoa is a major Taxonomy (biology), taxonomic group containing about 2,400 described species of Amoeba, amoeboid protists, often possessing blunt, fingerlike, Pseudopod#Morphology, lobose pseudopods and tubular mitochondrial cristae. In trad ...
for lobose amoebae and Rhizopoda for filose amoebae). Shortly after, phylogenetic analyses disproved this hypothesis, as non-amoeboid zooflagellates and amoeboflagellates were found to be completely intermingled with amoebae. With the addition of many flagellates to Rhizopoda and the removal of some amoebae, the name was rejected in favour of a new name
Cercozoa Cercozoa (now synonymised with Filosa) is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead united by phylogeny, molecular phylogenies of rRNA and actin or Ubiqu ...
. As such, both names Rhizopoda and Sarcodina were finally abandoned as formal taxa, but they remained useful as descriptive terms for amoebae. The phylum Amoebozoa was conserved, as it still primarily included amoeboid organisms, and now included the Mycetozoa.


Current classification

Today, amoebae are dispersed among many high-level taxonomic groups. The majority of traditional sarcodines are placed in two eukaryote supergroups:
Amoebozoa Amoebozoa is a major Taxonomy (biology), taxonomic group containing about 2,400 described species of Amoeba, amoeboid protists, often possessing blunt, fingerlike, Pseudopod#Morphology, lobose pseudopods and tubular mitochondrial cristae. In trad ...
and
Rhizaria The Rhizaria are a diverse and species-rich clade of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus '' Paulinella'' in the phylum Cercozoa, they are all non-photosynthetic, but many Foraminifera ...
. The rest have been distributed among the excavates, opisthokonts,
stramenopiles The stramenopiles, also called heterokonts, are Protist, protists distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular sur ...
and minor clades. *
Amoebozoa Amoebozoa is a major Taxonomy (biology), taxonomic group containing about 2,400 described species of Amoeba, amoeboid protists, often possessing blunt, fingerlike, Pseudopod#Morphology, lobose pseudopods and tubular mitochondrial cristae. In trad ...
: includes all naked and testate lobose amoebae (traditional Lobosea) as well as the pelobionts and
eumycetozoa Eumycetozoa (), or true slime molds, is a diverse group of protists that behave as slime molds and develop fruiting bodies, either as sorocarps or as sporocarp (fungi), sporocarps. It is a monophyletic group or clade within the phylum Amoebozoa t ...
ns, and a few flagellates. *
Rhizaria The Rhizaria are a diverse and species-rich clade of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus '' Paulinella'' in the phylum Cercozoa, they are all non-photosynthetic, but many Foraminifera ...
: includes amoebae bearing reticulose or filose pseudopodia, the majority of which were traditionally classified as Filosea, Granuloreticulosea and Actinopoda, such as Euglyphida,
Gromiida Gromiida is an order of Endomyxa. It is the only order in the class Gromiidea. Taxonomy Class Gromiidea Cavalier-Smith 2003 sensu Bass et al. 2009 * Order Gromiida Claparède & Lachmann 1856 s.s. ** Family Gromiidae Ruess 1862 romiina Delage ...
,
Radiolaria The Radiolaria, also called Radiozoa, are unicellular eukaryotes of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ect ...
, Proteomyxidea, Phaeodarea and
Foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...
(including
Xenophyophorea Xenophyophorea is a clade of foraminiferans. Xenophyophores are multinucleate unicellular organisms found on the ocean floor throughout the world's oceans, at depths of . They are a kind of foraminiferan that extract minerals from their surround ...
). It also houses a large diversity of free-living flagellates, amoeboflagellates and parasites like the Plasmodiophorida. * Heterolobosea : amoebae with lobose pseudopodia but eruptive flow of cytoplasm. Currently it includes the aggregative Acrasida, as well as several other amoeboflagellates. They are a class of excavates closely related to
Euglenozoa Euglenozoa are a large group of flagellate Discoba. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans. Euglenozoa are represented by four major groups, ''i.e.,'' Kinetoplastea, ...
, with whom they share their characteristic discoidal mitochondrial cristae. *
Stramenopiles The stramenopiles, also called heterokonts, are Protist, protists distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular sur ...
: although primarily composed by flagellates, it contains a few groups of amoebae. For example: the
Actinophryida The actinophryids are an order of heliozoa, a polyphyletic array of stramenopiles, having a close relationship with pedinellids and ''Ciliophrys''. They are common in fresh water and occasionally found in marine and soil habitats. Actinophryids a ...
, an order with typical heliozoan morphology; the amoeboid '' Rhizochromulina'', a genus of chrysophytes; or '' Synchroma'', a genus of amoeboid algae with reticulate axopodia. * Rotosphaerida : also known as
nucleariid The nucleariids, or nucleariid amoebae, are a group of amoebae that compose the sister clade of the fungi. Together, they form the clade Holomycota. They are aquatic organisms found in freshwater and marine habitats, as well as in faeces. They ...
s, includes a few filose amoebae traditionally classified within the Filosea, positioned as the sister group of
Fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
. * Centroplasthelida : heliozoans with a centroplast from which axopodia arise. They are closely related to the haptophyte algae inside the supergroup
Haptista Haptista is a proposed group of protists made up of centrohelids and haptophytes. Phylogenomic studies indicate that Haptista, together with ''Ancoracysta twista'', forms a sister clade to the SAR supergroup#Internal phylogeny, TSAR Supergroup (b ...
. * Rigifilida : a small order of filose amoebae previously interpreted as nucleariids. Together with the flagellate orders Mantamonadida and
Diphylleida Collodictyonidae (also Diphylleidae) is a group of aquatic, unicellular Eukaryote, eukaryotic organisms with two to four terminal Flagellum, flagella. They feed by phagocytosis, ingesting other unicellular organisms like algae and bacteria. Rec ...
, it composes the
CRuMs CRuMs is a clade of microbial eukaryotes, whose name is an acronym of the following constituent groups: i) Diphylleids, ii) rigifilids and iii) mantamonads as sister of the Amorphea. A new CRuMs order Glissandrida was proposed in 2025 to pla ...
clade, positioned closest to
Amorphea Amorphea is a taxonomic supergroup that includes the basal Amoebozoa and Obazoa. That latter contains the Opisthokonta, which includes the fungi, animals and the choanoflagellates. The taxonomic affinities of the members of this clade were ...
. * Breviatea : includes enigmatic free-living amoeboflagellates related to opisthokonts. The following cladogram shows the sparse positions of amoeboid groups (in bold), based on molecular phylogenetic analyses:


Amoeboid cells in other organisms


Amoeboid cell types in multicellular organisms

Some
multicellular organisms A multicellular organism is an organism that consists of more than one cell, unlike unicellular organisms. All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- and pa ...
have amoeboid cells only in certain phases of life, or use amoeboid movements for specialized functions. In the immune system of humans and other animals, amoeboid
white blood cells White blood cells (scientific name leukocytes), also called immune cells or immunocytes, are cells of the immune system that are involved in protecting the body against both infectious disease and foreign entities. White blood cells are genera ...
pursue invading organisms, such as bacteria and pathogenic protists, and engulf them by
phagocytosis Phagocytosis () is the process by which a cell (biology), cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs ph ...
.
Sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...
s exhibit a
totipotent Cell potency is a cell's ability to differentiate into other cell types. The more cell types a cell can differentiate into, the greater its potency. Potency is also described as the gene activation potential within a cell, which like a continuum ...
cell type known as
archaeocyte Archaeocytes (from Greek language, Greek '':wikt:ἀρχαῖος, archaios'' "beginning" and '':wikt:κύτος, kytos'' "hollow vessel") or amoebocytes are Amoebocyte, amoeboid cells found in Sea sponge, sponges. They are Totipotency, totipote ...
s, capable of transforming into the feeding cells or
choanocyte Choanocytes (also known as "collar cells") are cells that line the interior of asconoid, syconoid and leuconoid body types of sponges that contain a central flagellum, or ''cilium,'' surrounded by a collar of microvilli which are connected by ...
s.


Amoeboid dispersal stages

Amoeboid stages also occur in the multicellular fungus-like protists, the so-called
slime mould Slime mold or slime mould is an informal name given to a polyphyletic assemblage of unrelated eukaryotic organisms in the Stramenopiles, Rhizaria, Discoba, Amoebozoa and Holomycota clades. Most are near-microscopic; those in the Myxogastria ...
s. Both the plasmodial slime moulds, currently classified in the class
Myxogastria Myxogastria/Myxogastrea (myxogastrids, ICZN) or Myxomycetes ( ICN) is a class of slime molds that contains 5  orders, 14  families, 62 genera, and 888 species. They are colloquially known as the ''plasmodial'' or ''acellula ...
, and the cellular slime moulds of the groups Acrasida and Dictyosteliida, live as amoebae during their feeding stage. The amoeboid cells of the former combine to form a giant
multinucleate Multinucleate cells (also known as multinucleated cells or polynuclear cells) are eukaryotic cells that have more than one nucleus, i.e., multiple nuclei share one common cytoplasm. Mitosis in multinucleate cells can occur either in a coordinate ...
organism, while the cells of the latter live separately until food runs out, at which time the amoebae aggregate to form a multicellular migrating "slug" which functions as a single organism. Other organisms may also present amoeboid cells during certain life-cycle stages, e.g., the gametes of some green algae ( Zygnematophyceae) and pennate
diatoms A diatom (Neo-Latin ''diatoma'') is any member of a large group comprising several Genus, genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of Earth's B ...
, the spores (or dispersal phases) of some Mesomycetozoea, and the sporoplasm stage of
Myxozoa Myxozoa (etymology: Greek: μύξα ''myxa'' "slime" or "mucus" + thematic vowel o + ζῷον ''zoon'' "animal") is a subphylum of aquatic cnidarian animals – all obligate parasites. It contains the smallest animals ever known to have lived. ...
and of Ascetosporea.


References


Further reading

*Walochnik, J. & Aspöck, H. (2007)
Amöben: Paradebeispiele für Probleme der Phylogenetik, Klassifikation und Nomenklatur
''Denisia'' 20: 323–350. (In German)


External links


Amoebae: Protists Which Move and Feed Using Pseudopodia
at the Tree of Life web project * Siemensma, F
Microworld: world of amoeboid organisms
* Völcker, E. & Clauß, S
Visual key to amoeboid morphotypes
Penard Labs.

website of Maciver Lab of the University of Edinburgh, brings together information from published sources.

– informative amoeba videos. {{Authority control * Cell biology Motile cells Microbiology Microorganisms Eukaryote morphology Protists