Amoebozoa

Cochliopodium sp., copyright Proyecto Agua.

Belongs within: Amorphea.
Contains: Variosea, Eumycetozoa, Tubulinea, Archamoebae, Centramoebia, Thecamoebida, Vannellida, Paramoebidae.

The Amoebozoa are a clade of primarily unicellular eukaryotes in which most members have an amoeboid stage in their life cycle; some are exclusively amoeboid. Members of the clade Eudiscosea produce flattened pseudopodia with a polyaxial cytoplasmic flow or lacking a pronounced axis, and so far as known lack a ciliated stage (Adl et al. 2019).

The diversity of slime moulds
Published 10 September 2008
Life cycle of a plasmodial slime mould, from here.

How could you not love an organism that manages to combine both slime and mould? Slime moulds are saprobic organisms (i.e. they gain their nutrients by breaking down dead organic matter) that spend most of their life cycle feeding as separate amoeboid cells or disaggregated plasmodium. However, when conditions become right all the cells or plasmodium near each other will stream together to form a fungus-like fruiting body that releases spores. Because slime moulds thus resemble protozoa for part of their life cycle but fungi at other times, they were an early protagonist in the destruction of the idea that all organisms could be divided between plants and animals. Slime moulds, it turns out, are mostly not related to plants or animals. As our understanding of organismal phylogeny has progressed, it has become clear that not all slime moulds are even related to other slime moulds. Instead, the term has been used to cover a number of phylogenetically disparate organisms with little in common other than similar life cycles. However, the majority of references to slime moulds out there fail to mention this, focusing on only a small part of “slime mould” diversity, so I thought I’d give a brief overview of the full diversity of organisms with a slime mould-type life cycle.

Slime mould plasmodium, from here.

1—Myxogastrea: The plasmodial or acellular slime moulds, also known as Myxomycetes. This is the largest group of “slime moulds”—both in terms of number of species and the size reached by some species. While most other groups of slime moulds are fairly microscopic, myxogastreans reach sizes where they can easily be seen with the naked eye, at which point they are usually mistaken for fungi. During the feeding stage of their life cycle, myxogastreans form a plasmodium—a spreading mass that is not divided into individual cells, like threads of jelly or mucus. Recent phylogenetic analyses agree that myxogastreans belong to the Amoebozoa, the clade that includes more familiar amoeboids such as, well Amoeba (Cavalier-Smith et al. 2004). Indeed, the amoeboflagellate genus Hyperamoeba has been shown to represent a polyphyletic assortment of myxogastreans that have dropped the plasmodial habit.

2—Dictyostelia: While myxogastreans may be the largest group of slime moulds, dictyostelians may be the most famous, because they take the standard coolness of the slime mould life cycle and turn the dial up to eleven. The photo above (from here) shows the various stages of the life cycle of the most famous dictyostelian, Dictyostelium discoideum. Dictyostelians are cellular slime moulds—while myxogastreans form a plasmodium, dictyostelians spend their nutritive phase as separate individual amoeboids. When the time comes for reproduction, the separate amoeboids swarm together to form a slug-shaped mass that actually moves as one, like something out of a Japanese cartoon. The dictyostelian slug crawls around until it finds a suitable location, at which point it extends outwards to form a sporangium on the end of a long thin stalk. The complexities of Dictyostelium‘s life cycle have made it a favoured study organism for such topics as kin selection, as researchers attempt to identify what cues incite slug formation, and why some individual amoeboids forming the sporangium stalk are seemingly willing to sacrifice their own reproductive potential in order to promote the reproduction of those cells forming the sporangium.

Phylogenetically, dictyostelians are also amoebozoans, closely related to myxogastreans. However, analyses are currently unable to resolve whether amoebozoan slime moulds share a single origin (forming a clade called Mycetozoa) or whether dictyostelians and myxogastreans independently originated from closely related but separate amoeboid ancestors.

Ceratiomyxa species, photographed by Keisotyo.

3—Protostelia: Three small families of slime moulds, the Protosteliidae, Cavosteliidae and Ceratiomyxidae, form a spreading nutritive phase similar to that of the Myxogastrea, and have often been regarded as closely related to the ultrastructurally similar myxogastreans. However, while myxogastreans form a truly acellular plasmodium, different protostelians form a pseudoplasmodium, with cells retaining their individual identity (Protosteliidae and Cavosteliidae), or a plasmodium that breaks up into individual cells before sporangium formation (Ceratiomyxidae). Ceratiomyxidae form small coral-like fruiting bodies while Protosteliidae form minute sporangia on slender stalks like dictyostelians. If mycetozoans form a single group, protostelians may represent a morphological connection between the cellular dictyostelians and the acellular myxogastreans. A relationship between protostelians and other mycetozoans was supported by Baldauf (1999), but the group remains little studied. The protostelians themselves are of doubtful monophyly, and some families may be closer to myxogastreans than others.

4—Buddenbrockia: One parasitic animal was only recently identified as having a slime mould-like life cycle, with disassociated cells in its host aggregating together to give rise to a worm-like reproductive stage. The sordid details are covered elsewhere.

Acrasis fruiting bodies, from here.

5—Acrasea: Acrasids are cellular slime moulds like dictyostelians, and indeed were once united with dictyostelians under the name of Acrasiomycetes. Like dictyostelians, acrasids live as individual amoeboids that aggregate together to form raised sporangia. However, acrasids are ultrastructurally distinct from dictyostelians, and are not even amoebozoans—rather, they belong to a protozoan group called Heterolobosea that also includes Naegleria, the organism that causes amoeboid meningitis, and belongs to the Excavata eukaryote superclade. Whether or not it was due to the mistaken assumption that acrasids were closely related to the intensely studied Dictyostelium, or whether it was due to the fact that acrasids seem to be most often found growing on animal poo, studies of acrasids are laughably rare, and only Acrasis rosea appears to have received any recent attention.

6—Labyrinthulea: The slime nets are members of the Heterokonta, the clade also including brown and golden algae (among others), and have been covered elsewhere at this site.

One protist group, the Phytomyxa or Plasmodiophoromycota, has often been included with the slime moulds due to its formation of a plasmodium for part of its life-cycle. However, phytomyxans, which are parasites of plant roots belonging to the Rhizaria (the eukaryote superclade including foraminiferans and radiolarians), do not seem to have an aggregative phase of the life-cycle comparable to other slime moulds. The best known phytomyxan is Plasmodiophora brassicae, the cause of club root in cabbages and other brassicas.

7—Myxococcales: Finally comes a group that has never been regarded as slime moulds, but which has a very similar life cycle. The reason why Myxococcales have never been lumped with slime moulds is because they are not eukaryotes of any kind but bacteria. Myxococcales are saprobic bacteria generally found in soil. They are capable of gliding motility, a form of movement by means other than flagella, though the exact mechanism remains little known. When nutrient supplies run low, some species of Myxococcales are capable of swarming together in a similar manner to cellular slime moulds and releasing dispersive spores. Myxococcales are therefore one of the few groups of bacteria to have developed multicellularity.

Amoebozoan classification: putting the formless in formation
Published 4 September 2009
Chaos carolinense, the species generally regarded today as the main exemplar of the genus Chaos (see the note below). In case you were wondering, this individual is moving towards the right. Photo by David Patterson.

Previously, I described some of the oddities of the well-known micro-organism Amoeba. In this post, I’ll expand the field of view to look more generally at the clade of Amoebozoa. Study of amoeboids has certainly been going on for a long time—an amoeboid was among the few micro-organisms listed by Linnaeus (1758), under the name of Volvox chaos*. But how, you may be wondering, does one go about characterising a shapeless blob? And how does one distinguish one type of shapeless blob from another?

*Later raised by Linnaeus to the status of a separate genus, Chaos. The name Chaos is still in use for a genus very closely related to Amoeba (the main difference is that Chaos is multinucleate, while Amoeba has a single nucleus) but it pays not to look to carefully at the taxonomy. Debate about the identity of the original Volvox chaos raged down the years—whether it was the modern Chaos, the modern Amoeba, or something else entirely—but the debate was largely futile, because the original description cited by Linnaeus illustrates little more than a shapeless blob with a few dots over it. Many authors included the modern ‘Chaos‘ in the genus Pelomyxa, another large multinucleate amoeboid, but Pelomyxa is an entirely different beast. King & Jahn’s (1948) argument for recognition of the three genera Amoeba, Pelomyxa and Chaos with those names is in accord with the modern usage, but has the air more of arbitrary pragmatism rather than adherence to priority—the genus that is now Chaos needed a name, and the name Chaos was going begging. The modern usage is now well-established, and it wouldn’t really benefit anyone to go stirring things up now.

If you are wondering exactly that, then I’m sorry to point out to you that you’re under something of a misunderstanding about the nature of cellular structure. Not that I blame you, because it’s an easy enough misunderstanding to develop. Most basic descriptions of intra-cellular structure might suggest that the interior of a cell is basically liquid (or at most jelly-like) with the nucleus and other organelles freely floating about like so many chunks of carrots and peas in a vegetable soup. But while the cytoplasm is fluid, it’s not water. It’s a complex mixture of all sorts of molecules—actin filaments, microtubules, etc.—almost more like an enormous bowl of noodles than a broth. It is the interactions between these molecules that give a cell its shape, and also that make it move. The movement and shape-changes of an amoeboid are not random, but follow a pattern. And different types of amoeboid will move according to a different pattern. The form and manner that the amoeboid adopts while moving is generally one of the first things to observe in its identification.

Jahn et al. (1974) divided amoeboid micro-organisms into two classes based on the mode of pseudopodium formation. In one class (as shown in the figure from Jahn et al., 1974, above), the cytoplasm was liquified and pushed forward by contraction, re-coagulating at the front of the resulting broad, lobose pseudopodium. In the second class (shown in the figure below), long filamentous pseudopodia were extended with each side of the pseudopodium moving against the other in an opposite direction.

The distinction between lobose and filose amoeboids has been reinforced with further study, though as it turns out both modes have evolved multiple times (filose pseudopodia more often than lobose pseudopodia). Filose pseudopodia are found among such organisms as the Rhizaria (including foraminifers and radiolarians), while Amoebozoa are characterised by lobose pseudopodia (in those amoebozoans that don’t produce distinct pseudopodia, the entire cell moves in this way). Lobose pseudopodia are also found among the Heterolobosea, another group of micro-organisms not closely related to Amoebozoa (heteroloboseans include Naegleria, the causative agent for amoebic meningitis, and acrasid slime moulds). Nevertheless, pseudopodium formation differs between the two in that in amoebozoans, movement is smooth and continuous, while heteroloboseans produce pseudopodia eruptively, cycling between periods of extension and periods of “resting” (heteroloboseans also have a distinct mitochondrial structure from amoebozoans).

Acanthamoeba, a common amoebozoan in soil and fresh water, occasionally causing eye infections in humans. Acanthamoeba produce distinctive short, narrow subpseudopodia from the single flattened cell-wide pseudopodium, as seen in this photo by David Patterson.

Among amoebozoans except testate forms, archamoebae and slime moulds, Smirnov & Goodkov (1999) recognised nineteen “morphotypes” distinguished by their mode of movement—whether the amoeboid extends multiple pseudopodia, or moves as a single unit; the form of the uroid (the posterior end of the cell while the amoeboid is moving); whether the surface of the cell is ridged or smooth; and other such details. Though Smirnov & Goodkov (1999) explicitly established their morphotype distinctions as identification characters only, without necessarily indicating higher classification, molecular phylogenetic studies have indicated a rough (but not exact) correlation between locomotive mode and phylogeny (Smirnov et al. 2005). For instance, Tubulinea, the class of amoebozoans including Amoeba and Chaos, generally produce tubular or subcylindrical pseudopodia with cytoplasm streaming down a distinct single central axis. Members of another class, Flabellinea, have flattened pseudopodia without a single central axis.

Vannella simplex, a member of the Flabellinea. Note the single broad flat fan-shaped pseudopodium. Photo from here.

Not everything is movement, of course. Other features distinguishing amoebozoans include the texture and ornamentation (if any) of the outer cell surface; the shape, distribution and number of the nucleus/nuclei and other organelles; and the presence and nature of a protective test (interestingly, while the testate filose amoeboids do not appear to form a monophyletic group among the Rhizaria, the testate lobose amoebae do seem to be monophyletic among the Amoebozoa—Nikolaev et al. 2005). There is a good detailed online guide at Alexey Smirnov’s website (and a hat-tip to Psi Wavefunction for pointing the site out to me). A number of the higher taxa among the Amoebozoa have become reasonably robust in the last few years—if you’re not too completely sick of amoeboids, I may introduce you to a few over the next few posts.

Discosea: keeping a low profile
Published 11 September 2009
Various views of Vannella devonica, a representative of the Vannellidae, photographed by A. Smirnov.

Having covered the Tubulinea, it’s time to move on to some of the less familiar Amoebozoa. At this point, however, the competing classifications of Cavalier-Smith et al. (2004) and Smirnov et al. (2005) begin to part ways—at least superficially. Cavalier-Smith et al.‘s class Discosea is roughly comparable to Smirnov et al.‘s class Flabellinea, but the two are not identical. Rather, Flabellinea is a subgroup of Discosea, the latter also including a few taxa that Smirnov et al. listed as Amoebozoa incertae sedis. As such, I’ll use Discosea for the larger group and Flabellinea for the smaller group. Monophyly of the Flabellinea has been recovered in a number of analyses (including both the studies just cited), monophyly of the Discosea is more doubtful. Kudryavtsev et al. (2005) found a monophyletic Discosea, but all other molecular analyses including non-flabellinean ‘Discosea’ show ‘Discosea’ as polyphyletic. The morphological characteristics of Discosea cited by Cavalier-Smith et al. (2004) (“highly flattened, often discoid amoebae that move slowly by a leading lamellipodium“, and a tendency to secrete some sort of thickened protective covering or membrane) are not unique to members of the group. Nor is the other feature cited by Smirnov et al. (2005) as distinguishing Flabellinea from Tubulinea, that cytoplasmic flow in pseudopodia does not form a single central axis. Discoseans produce only a single anterior pseupodium when moving (which may or may not produce subpseudopodia), and no discosean has an adhesive uroid.

As well as the Flabellinea, Cavalier-Smith et al.‘s Discosea included the Cochliopodiidae and Thecamoebida. Later analysis (Kudryavtsev et al. 2005) suggested the polyphyly of Thecamoebida, and the discosean component was restricted to the genus Dermamoeba (nevertheless, because Dermamoeba and Thecamoeba are ultrastructurally similar, I may as well cover both in this post). Subsequent studies have continued to indicate the polyphyly of ‘Thecamoebida’, but Pawlowski (2008) refers to unpublished data that might restore monophyly to the group. Cavalier-Smith et al. (2004) also suggested that the multiciliate Multicilia was a discosean, but Nikolaev et al. (2006) have since shown otherwise (Multicilia will feature in the next Amoebozoa post; with its removal, Discosea becomes an entirely non-ciliate group). Finally, though its authors refrained from saying so, it seems entirely possible that, if the Discosea should be monophyletic, the recently described distinctive genus Pellita (Smirnov & Kudryavtsev 2005) may be discosean.

Thecamoeba striata, photographed by Keisotyo. I suspect that the front of the cell is towards the lower left.

A general characteristic of Amoebozoa that I have not yet had cause to mention is the presence of a glycocalyx, a protective covering of proteins and polysaccharides that lies outside but is connected to the membrane of the cell. The nature of the glycocalyx has often been used in differentiating amoebozoan taxa in the past, but recent studies suggest that it may be more variable than previously thought (e.g. Smirnov et al., 2007), so glycocalyx-based features should probably be treated with caution. Both ‘Thecamoebida’ and Flabellinea have particularly well-developed glycocalyces. In ‘Thecamoebida’, the glycocalyx is amorphous (probably the ancestral condition for Amoebozoa) but extremely thick. Thecamoebids on the move are generally oval or oblong in shape without anterior subpseudopodia. Thecamoeba has the dorsal surface of the cell shaped into longitudinal folds or wrinkles, while Dermamoeba has no dorsal folds or wrinkles (Smirnov & Goodkov, 1999).

Paramoeba aestuarina. The large dark spot is the “parasome” (or the endosymbiont Perkinsela amoebae, however you want to put it). Image from here.

In Flabellinea, the glycocalyx is usually differentiated into a covering of column-like glycostyles, though a number of flabellineans have lost the glycostyle coat (Smirnov et al., 2007). Flabellinea are divided into three families—Vanellidae, Paramoebidae and Vexilliferidae, with the latter two more closely related to each other than to Vanellidae. The basic form of Flabellinea is broad and fan-shaped; Vanellidae have a smooth leading edge without subpseudopodia, while Paramoebidae and Vexilliferidae produce subpseudopodia – short and blunt in Paramoebidae, long and slender in Vexilliferidae. Paramoebids were also distinguished in the past by their possession of a distinctive organelle known as the parasome. However, this distinction has been reworked in recent years—not because of doubts about the reality of the parasome, but because the parasome is now regarded as a separate organism in its own right, an endosymbiont rather than an organelle of paramoebids.

Diagram of Pellita, showing how the subpseudopodia extend through the thick cell coat, from Smirnov & Kudryavtsev (2005).

The recently discovered Pellita (Smirnov & Kudryavtsev 2005) resembles Flabellinea in possessing a cell covering of glycostyles. This covering is particularly thick in Pellita, and almost resembles a test rather than a coat. So thick is Pellita‘s covering that the normal means of amoebozoan movement and feeding via the projection of pseudopodia are not possible for it. Instead, Pellita produces short subpseudopodia with a covering of basic cell membrane only that muscle their way between the glycostyles until they project outside the coat. These subpseudopodia engulf individual bacteria if feeding, while for movement subpseudopodia produced near the leading edge of the cell adhere to the substrate and the cell rolls forward over the top of them.

Cochliopodium, from here.

Finally, the Cochliopodiidae also possess an external covering, but in their case it is a rigid coat that is entirely separate from the cell membrane. In the genus Cochliopodium the coat consists of carbohydrate scales, while in the genera Gocevia and Paragocevia the coat is filamentous. The cochliopodiid coat differs from the test of Arcellinida in that it is restricted to the dorsal surface of the cell, not surrounding it as in arcellinidans. Also, the coat is divided between the daughter cells when the cochliopodiid divides; in Arcellinida, one daughter cell keeps the test while the other has to make an entire new test from scratch.

Systematics of Amoebozoa

Characters (from Adl et al. 2012): Cells “naked” or testate; tubular mitochondrial cristae, often branched (ramicristate), secondarily lost in some; uninucleate, binucleate or multinucleate; cysts common, morphologically variable; sexual or asexual; many taxa exhibit either sporocarpic (single amoeboid cell differentiates into a usually stalked, subaerial structure that supports one to many propagules termed spores) or sorocarpic (amoebae aggregate into a multicellular mass that develops into a multicellular fruiting body) fruiting; or myxogastroid ciliated stages; when amoeboid, locomotion with non-eruptive morphologically variable pseudopodia; ancestrally bikont with many taxa exhibiting reduction of the bikinetid.

Amoebozoa (see below for synonymy)
    |--EvoseaAB19
    |    |--Semiconosia (see below for synonymy)C-SCL16
    |    |    |--VarioseaTA16
    |    |    `--EumycetozoaTA16
    |    `--+--+--TubulineaTA16
    |       |  `--ArchamoebaeTA16
    |       `--+--+--Pessonella marginataTA16, SX97
    |          |  `--Cutosa [Cutosea]C-SCL16
    |          |       |--ArmaparvusAB19
    |          |       |--Squamamoeba Kudryavtsev & Pawlowski 2013 [Squamamoebidae]C-SCL16
    |          |       |    `--S. japonicaC-SCL16
    |          |       `--Sapocribrum Lahr et al. 2015TA16, C-SCL16 [Sapocribridae]
    |          |            `--S. chincoteaguenseC-SCL16
    |          `--Himatismenida [Cochliopodidae, Cochliopodiidae, Cochliopodiinae, Pseudonebelinae, Tectiferina]TA16
    |               |  i. s.: Chlamydamoeba Collin 1912LT64
    |               |           `--*C. tentaculifera Collin 1912LT64
    |               |         CoenopodiumC-SCL16
    |               |--Ovalopodium desertumTA16
    |               `--+--Parvamoeba [Parvamoebidae, Parvamoebina]TA16
    |                  |    |--P. monouraTA16
    |                  |    `--P. rugataC-SCL16
    |                  `--Cochliopodium Hertwig & Lesser 1874TA16, KB05 [=Kochliopodium (l. c.)LT64]
    |                       |--C. bilimbosum (Auerbach 1856) (see below for synonymy)LT64
    |                       |--C. gulosumC-SCO04
    |                       |--C. longispinumSX97
    |                       |--C. minus Page 1976KB05
    |                       |--C. minutoidumC-SCL15
    |                       |--C. minutum West 1901KB05
    |                       `--C. spiniferum Kudryatsev 2004KB05
    `--Eudiscosea [Discosea, Longamoebia]C-SCL16
         |--CentramoebiaAS12
         `--DiscoseaAB19
              |  i. s.: Mycamoeba Blandenier et al. 2017AB19
              |           `--M. gemmiparaAB19
              |--ThecamoebidaAS12
              `--Flabellinea [Flabellina, Flabellinia, Glycostylida, Vanelloidea]TA16
                   |--VannellidaC-SCL16
                   `--Dactylopodida [Conopodina, Dactylopodina, Paramoeboidea]TA16
                        |  i. s.: BoveellaAS12
                        |         DactylosphaeriumAS12
                        |         OscillodignumAS12
                        |         Podostoma filigerumAS12, G89
                        |         StrioluatusAS12
                        |         Subulamoeba saphirinaAS12, SX97
                        |         TrienamoebaAS12
                        |--ParamoebidaeC-SCL16
                        `--+--Vexillifera [Vexilliferidae]C-SCL16
                           |    |--V. armataSN05
                           |    |--V. bacillipedesSN05
                           |    `--V. minutissimaSN05
                           `--DermamoebidaC-SCL16
                                |--DermamoebidaeC-SCL16
                                |    |--Dermamoeba algensisC-SCL16
                                |    `--ParadermamoebaC-SCL16
                                `--Mayorella [Mayorellida, Mayorellidae, Mayorellina]TA16
                                     |--M. gemmiferaC-SCL16
                                     |--M. inquisitaSX97
                                     |--M. penardiMS98
                                     |--M. ripariaLB90
                                     `--M. spatulaSX97
Amoebozoa incertae sedis:
  Malamoeba locustaeSN05, R91
  MalpighamoebaSN05
  PansporellaAS12 [PansporellidaeLT64, Sporamoebidae]
  GibbodiscusAS12
  Protamoeba vorax Gruber 1884G84
  BelonocystisAB19
  Gymnophryidae [Araudia, Biomyxida, Gymnophrea, Reticulosida]C-SC03
    |--Gymnophrys cometaNB04
    |--Borkovia desaedeleeriC-SC03, M00
    `--Biomyxa Leidy 1875AB19, LT64 [Biomyxidae]
         `--*B. vagans Leidy 1875LT64 [incl. Amoeba porrectaG84]
  OscillosignumAB19
  Schoutedamoeba minuta Van Vichelin et al. 2016AB19

Amoebozoa [Acanthopodina, Addiffluentia, Amastigogeninia, Amebea, Amoebaea, Amoebeae, Amoebiae, Amoebida, Amoeboea, Chaetoproteida, Chaetoproteidae, Chaoinea, Conosa, Conosea, Diffluentia, Glycopoda, Gymnamoebaea, Gymnamoebia, Gymnamoebida, Gymnamoebina, Lobosa, Lobosia, Monamoebidae, Monamoebina, Monostega, Monostegia, Pelomyxacea, Pharopodida, Protamoebae, Proteina, Protomyxidae, Protosteliales, Protosteliomycetes, Testacealobosea, Testamoebida, Thecamoebina, Thecina]

Cochliopodium bilimbosum (Auerbach 1856) [=Amoeba bilimbosa; incl. *C. pellucidum Hertwig & Lesser 1874]LT64

Semiconosia [Ceratiomyxacea, Ceratiomyxaceae, Ceratiomyxales, Ceratiomyxioidea, Ectosporeae, Eumyxa, Exosporae, Exosporales, Exosporea, Exosporeen, Exosporei, Exosporinei, Parastelida]C-SCL16

*Type species of generic name indicated

References

[AB19] Adl, S. M., D. Bass, C. E. Lane, J. Lukeš, C. L. Schoch, A. Smirnov, S. Agatha, C. Berney, M. W. Brown, F. Burki, P. Cárdenas, I. Čepička, L. Chistyakova, J. del Campo, M. Dunthorn, B. Edvardsen, Y. Eglit, L. Guillou, V. Hampl, A. A. Heiss, M. Hoppenrath, T. Y. James, A. Karnkowska, S. Karpov, E. Kim, M. Kolisko, A. Kudryavtsev, D. J. G. Lahr, E. Lara, L. Le Gall, D. H. Lynn, D. G. Mann, R. Massana, E. A. D. Mitchell, C. Morrow, J. S. Park, J. W. Pawlowski, M. J. Powell, D. J. Richter, S. Rueckert, L. Shadwick, S. Shimano, F. W. Spiegel, G. Torruella, N. Youssef, V. Zlatogursky & Q. Zhang. 2019. Revisions to the classification, nomenclature, and diversity of eukaryotes. Journal of Eukaryotic Microbiology 66: 4–119.

[AS12] Adl, S. M., A. G. B. Simpson, C. E. Lane, J. Lukeš, D. Bass, S. S. Bowser, M. W. Brown, F. Burki, M. Dunthorn, V. Hampl, A. Heiss, M. Hoppenrath, E. Lara, E. Le Gall, D. H. Lynn, H. McManus, E. A. D. Mitchell, S. E. Mozley-Stanridge, L. W. Parfrey, J. Pawlowski, S. Rueckert, L. Shadwick, C. L. Schoch, A. Smirnov & F. W. Spiegel. 2012. The revised classification of eukaryotes. Journal of Eukaryotic Microbiology 59 (5): 429–493.

Baldauf, S. L. 1999. A search for the origins of animals and fungi: comparing and combining molecular data. American Naturalist 154 (S4): 178–188.

[C-SC03] Cavalier-Smith, T., & E. E.-Y. Chao. 2003. Phylogeny and classification of phylum Cercozoa. Protist 154: 341–358.

[C-SCL15] Cavalier-Smith, T., E. E. Chao & R. Lewis. 2015. Multiple origins of Heliozoa from flagellate ancestors: new cryptist subphylum Corbihelia, superclass Corbistoma, and monophyly of Haptista, Cryptista, Hacrobia and Chromista. Molecular Phylogenetics and Evolution 93: 331–362.

[C-SCL16] Cavalier-Smith, T., E. E. Chao & R. Lewis. 2016. 187-gene phylogeny of protozoan phylum Amoebozoa reveals a new class (Cutosea) of deep-branching, ultrastructurally unique, enveloped marine Lobosa and clarifies amoeba evolution. Molecular Phylogenetics and Evolution 99: 275–296.

[C-SCO04] Cavalier-Smith, T., E. E.-Y. Chao & B. Oates. 2004. Molecular phylogeny of Amoebozoa and the evolutionary significance of the unikont Phalansterium. European Journal of Protistology 40: 21–48.

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