Filasterea
Single-celled amoeboids key to animal origins.
Last updated
Multicellgenome Lab · CC BY 2.0
Filasterea is a group of single-celled, amoeba-like eukaryotes that belong to the basal filozoan lineage. It includes the genera Ministeria and Capsaspora. This clade is a sister group to Choanoflagellata + Metazoa (animals), not to the outdated or paraphyletic grouping Choanozoa.
The name Filasterea was first proposed in 2008 by Shalchian-Tabrizi and colleagues, based on an analysis of 78 genes. Their work placed Filasterea as the sister group to the combined clade of Metazoa and Choanoflagellata within the Opisthokonta. Later studies with more species have supported this finding.
Etymology
The name comes from Latin filum (thread) and Greek aster (star), referring to the key features shared by all members: small, round amoeboid cells with a single nucleus, covered in long, radiating projections called filopodia. These thread-like extensions likely help with sticking to surfaces and capturing prey.
Applications
Only two filasterean species are currently kept in culture: Capsaspora owczarzaki, originally found inside a freshwater snail, and Ministeria vibrans, a free-living marine bacterium-eater. Complete genome sequences exist for C. owczarzaki, M. vibrans, Pigoraptor vietnamica, and Pigoraptor chileana. Comparative studies show that Filasterea are important for understanding the genetic toolkit of the single-celled ancestor of animals and for shedding light on how animals (Metazoa) originated. Metabarcoding analyses of 18S ribosomal RNA in marine environments, such as those by del Campo & Ruiz-Trillo (2013), have successfully recovered filasterean representatives, indicating the group is present in nature.
Taxonomically, Filasterea is classified as a class (Filasterea Shalchian-Tabrizi et al. 2008), containing the order Ministeriida (Cavalier-Smith 1997). Within that order are families Ministeriidae (Cavalier-Smith 2008) with genus Ministeria (species M. marisola and M. vibrans); Txikisporidae (Urrutia, Feist & Bass 2021) with genus Txikispora (species T. philomaios); and Capsasporidae (Cavalier-Smith 2008) with genera Capsaspora (species C. owczarzaki) and Pigoraptor (species P. chileana and P. vietnamica). Established phylogeny places Capsaspora and Ministeria as sister genera within Filasterea, not with one being more closely related to Choanozoa.
Scientific classification
- CladeEukaryota
- CladeObazoa
- CladeHolozoa
- ClassFilasterea
Named by Salchian-Tabrizi et al. 2008
Sources: Wikipedia taxobox: Filasterea (CC BY-SA 4.0)
Quick Facts
- Type
- Clade of single-celled amoeboid eukaryotes
- Proposed by
- Shalchian-Tabrizi et al.
- Includes genera
- Ministeria
- Capsaspora
- Txikispora
- Pigoraptor
Facts from the source article.
Discovery & Phylogenetic Placement
In 2008, Shalchian-Tabrizi and co-authors introduced a new clade using a phylogenomic framework built on 78 genes. Their analysis grouped together single-celled ameboid eukaryotes—including the genera Ministeria and Capsaspora—and placed them as a basal lineage within the filozoans. The most consequential finding was the positioning of this clade as the sister group to the Choanozoa, the branch from which both choanoflagellates and multicellular animals emerged.
In broader opisthokont terms, Filasterea sits as the sister group to the combined Metazoa-plus-Choanoflagellata clade. Later phylogenetic studies that incorporated more taxon-rich datasets have independently corroborated this sister-group relationship, reinforcing its reliability. The shift from earlier, gene-poor reconstructions to multi-gene phylogenomics was essential for resolving this node, and the repeated confirmation across independent analyses has made the Filasterea–Choanozoa split one of the more robustly supported relationships in the opisthokont tree of life.
Morphology & the Meaning Behind the Name
The very name Filasterea encodes the morphology that unites every member of the clade. The Latin root filum, meaning thread, combined with the Greek aster, meaning star, evokes the characteristic appearance of these organisms: small, rounded, single-nucleated amoeboid cells whose surfaces are studded with long, radiating filopodia. These thread-like protrusions extend outward in a star-like pattern, giving the cell a distinctive silhouette under the microscope.
Beyond their visual role, the filopodia likely serve functional purposes in substrate adhesion and in the capture of prey, anchoring the cell to surfaces while simultaneously extending a net to ensnare smaller organisms. This combination of a compact, mononucleated body with an elaborate crown of filopodia distinguishes filastereans from many other ameboid lineages and provides the morphological basis for the clade's name. The consistency of this body plan across the known genera—Ministeria, Capsaspora, Pigoraptor, and Txikispora—underscores that the thread-and-star architecture is a shared ancestral trait rather than a convergent adaptation.
Genomic Windows into Animal Ancestry
Complete genome sequences have now been determined for four filasterean species: Capsaspora owczarzaki, Ministeria vibrans, Pigoraptor vietnamica, and Pigoraptor chileana. These genomic resources have proven invaluable for comparative analyses aimed at reconstructing the genetic toolkit of the unicellular ancestor that gave rise to animals.
Because Filasterea occupies the sister position to the Metazoa-plus-Choanoflagellata clade, its genomes serve as a critical outgroup reference: genes present in filastereans but absent in animals likely predate the metazoan lineage, while those shared across both branches illuminate the ancestral repertoire from which multicellularity evolved. In this way, filasterean genomics provides a window into the molecular landscape immediately preceding the origin of Metazoa. The availability of multiple genomes from different genera also allows researchers to distinguish lineage-specific innovations from features already established in the common filozoan ancestor, sharpening our understanding of which genetic changes accompanied the transition from single cells to the first animals.
Ecological Footprint & Taxonomic Breadth
Despite their phylogenetic importance, filastereans remain elusive in the natural world. Only two species have been maintained in laboratory culture: Capsaspora owczarzaki, originally isolated from within a freshwater snail, and Ministeria vibrans, a free-living marine bacteriovore. The broader taxonomy now recognizes additional genera and species—Ministeria marisola, Txikispora philomaios, Pigoraptor chileana, and Pigoraptor vietnamica—though these have not all been cultured.
Metabarcoding surveys targeting 18S ribosomal RNA in marine environments have repeatedly failed to recover filasterean sequences, suggesting that the clade is not particularly abundant in the ecosystems sampled. This scarcity in environmental DNA, contrasted with the clear phylogenetic signal in phylogenomic trees, hints that filastereans may occupy specialized microhabitats or exist at low population densities. One further nuance in the literature is that some analyses place Capsaspora closer to Choanozoa than to Ministeria, a finding that, if confirmed, would refine the internal branching order within the clade.
Frequently Asked Questions
What exactly is Filasterea?
Filasterea is a clade of free-living, amoeba-shaped single-celled eukaryotes that sits at the base of the filozoan lineage. It is not a multicellular organism or a colony but a group of closely related protist species.
How does Filasterea relate to animals and choanoflagellates?
Filasterea is the sister group to the combined clade of Choanoflagellata plus Metazoa, meaning it diverged just before the last common ancestor of those two lineages. It is not the sister to the older, paraphyletic term 'Choanozoa,' which lumps together more than one distinct lineage.
Which genera are recognized within Filasterea?
The clade currently encompasses genera such as Ministeria, Capsaspora, Txikispora, and Pigoraptor. All are motile, amoeboid protists that lack a flagellum in their typical life cycle.
More in Higher-Level Taxonomy & Evolution
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Filasterea (CC BY-SA 4.0).
- Word definitions: the , each quoted from its Wikipedia article.
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced