# Acrasidae
**Acrasidae** is a family of heterolobosean amoebae, established by Philippe van Tieghem in 1880, whose members are sorocarpic amoebae often called cellular slime molds: free-living predatory amoebae that, on starvation, aggregate to build a multicellular fruiting body (sorocarp) bearing spores.[1](https://www.sciencedirect.com/science/article/pii/S0932473911000757) • [2](https://www.sciencedirect.com/science/article/pii/S1434461010000805) In the modern restricted sense the family contains the genera *Acrasis* and the closely similar *Pocheina*.[1](https://www.sciencedirect.com/science/article/pii/S0932473911000757)
| Key fact | Detail |
|---|---|
| Established | Family Acrasidae van Tieghem, 1880; originally grouped with dictyostelids in the Acrasiées[1](https://www.sciencedirect.com/science/article/pii/S0932473911000757) |
| Modern circumscription | Page and Blanton (1985) restricted the family to *Acrasis* and *Pocheina*, excluding dictyostelids, *Copromyxa*, and *Fonticula*[1](https://www.sciencedirect.com/science/article/pii/S0932473911000757) |
| Phylogenetic placement | Heterolobosea (Excavata), supported by glyceraldehyde-3-phosphate dehydrogenase gene analysis grouping acrasids with Vahlkamfiidae[3](https://www.sciencedirect.com/topics/immunology-and-microbiology/cellular-slime-mold) |
| Relationship to other slime molds | Entirely unrelated to dictyostelid and myxogastrid slime molds on both ultrastructural and molecular data[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC23686/) |
| Trophic ecology | Aggressive micro-predators, about 8 to 10 times larger and faster than dictyostelid amoebae, probably preying mostly on eukaryotic microbes[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC11589745/) |
| Fossil record | *Pusillocyclops aimei* gen. et sp. nov., a mid-Cretaceous Burmese amber acrasid with cellular sporocarps bearing an apical sorus of a single spherical spore[6](https://www.ars.usda.gov/research/publications/publication/?seqNo115=361455) |
## Life cycle and fruiting bodies
Acrasids spend their trophic phase as amoebae. When populations starve, the amoebae aggregate and surround themselves with an extracellular slime sheath, then develop into a multicellular fruiting body called a sorocarp.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC11589745/) The name "cellular slime mold" reflects this habit: unlike the plasmodial slime molds, which form a single multinucleate mass, the aggregate is built of individual cells that remain distinct.[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC23686/)
The fossil acrasid *Pusillocyclops aimei* shows the characteristic architecture preserved in amber: a fructification with cellular sporocarps bearing an apical sorus containing a single spherical spore.[6](https://www.ars.usda.gov/research/publications/publication/?seqNo115=361455)
## Ecology and behavior
**Predatory amoebae.** Acrasid amoebae are aggressive micro-predators, roughly 8 to 10 times larger and faster than dictyostelid amoebae, and probably prey mostly on eukaryotic microbes; dictyostelids, by contrast, are primarily bacteriovores.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC11589745/) This difference in feeding biology accompanies the deep genetic separation between the two groups.
## Taxonomic history
The history of the acrasids is a story of narrowing. Van Tieghem's 1880 account grouped the aggregative amoebae of *Acrasis*, *Pocheina*, and the dictyostelids together as Acrasiées, distinguishing them from the Myxogastria by the lack of a true plasmodium.[1](https://www.sciencedirect.com/science/article/pii/S0932473911000757) Over the following 130 years, various authors placed a shifting set of organisms among the acrasids, including *Copromyxa*, *Copromyxella*, *Fonticula*, and the nonaggregative fruiting amoebae *Protostelium* and *Sappinia*.[1](https://www.sciencedirect.com/science/article/pii/S0932473911000757)
Page and Blanton's 1985 interpretation, based on morphological and developmental details, restricted the Acrasidae to *Acrasis* and *Pocheina* and specifically excluded the dictyostelids, *Copromyxa*, and *Fonticula*, although Blanton (1990) still used the broader Acrasea semi-formally.[1](https://www.sciencedirect.com/science/article/pii/S0932473911000757) Emphasis on the movement and behavior of the amoebae had already led several workers to suggest a close relationship to organisms with limax-type amoebae, such as *Naegleria* species and the vahlkampfiids.[3](https://www.sciencedirect.com/topics/immunology-and-microbiology/cellular-slime-mold)
## Phylogenetic position
Molecular data settled the question of affinity. A phylogenetic analysis of genes encoding glyceraldehyde-3-phosphate dehydrogenase, including the acrasid *Acrasis rosea*, the dictyostelid *Dictyostelium discoideum*, and the schizopyrenid *Naegleria andersoni*, supported the grouping of acrasids in the Heterolobosa with Vahlkamfiidae.[3](https://www.sciencedirect.com/topics/immunology-and-microbiology/cellular-slime-mold) • [7](https://pubmed.ncbi.nlm.nih.gov/8976605/) Ultrastructure agrees: acrasids lack dictyosomes, and their mitochondria have discoid cristae and are surrounded by rough endoplasmic reticulum.[8](https://www.nies.go.jp/chiiki1/protoz/systemat/anot-pro/ref-5753.htm) The mitotic apparatus of *Acrasis rosea* is very different from those of other slime molds.[3](https://www.sciencedirect.com/topics/immunology-and-microbiology/cellular-slime-mold)
The broader lesson is that "cellular slime mold" is a lifestyle description, not a lineage. Molecular phylogenies place the aggregatively fruiting amoebae in three of the six eukaryotic supergroups: dictyostelids in [Amoebozoa](https://www.edgepedia.org/amoebozoa), *Acrasis* in Excavata, and *Fonticula* in Opisthokonta.[2](https://www.sciencedirect.com/science/article/pii/S1434461010000805) The Acrasids therefore appear entirely unrelated to the dictyostelid and myxogastrid slime molds on both ultrastructural and molecular data.[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC23686/)
## Genomics
The genome and developmental transcriptomes of *Acrasis kona* have been used to examine the deep origins of eukaryotic multicellular pathways, making the acrasids a comparative outgroup for studying how independent lineages of amoebae converged on multicellular fruiting.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC11589745/)
## References
1. [A contemporary evaluation of the acrasids (Acrasidae, Heterolobosea, Excavata), ScienceDirect](https://www.sciencedirect.com/science/article/pii/S0932473911000757)
2. ["Slime Molds" among the Tubulinea (Amoebozoa): Molecular Systematics and Taxonomy of Copromyxa, ScienceDirect](https://www.sciencedirect.com/science/article/pii/S1434461010000805)
3. [Cellular Slime Mold - an overview, ScienceDirect Topics](https://www.sciencedirect.com/topics/immunology-and-microbiology/cellular-slime-mold)
4. [Origin and evolution of the slime molds (Mycetozoa), PNAS via PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC23686/)
5. [The Acrasis kona genome and developmental transcriptomes reveal deep origins of eukaryotic multicellular pathways, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11589745/)
6. [USDA ARS publication: dictyostelid and acrasid slime molds from mid-Cretaceous Burmese amber](https://www.ars.usda.gov/research/publications/publication/?seqNo115=361455)
7. [Evidence for the Heterolobosea from phylogenetic analysis of genes encoding glyceraldehyde-3-phosphate dehydrogenase, PubMed](https://pubmed.ncbi.nlm.nih.gov/8976605/)
8. [Systematics (ref. ID; 5753), NIES](https://www.nies.go.jp/chiiki1/protoz/systemat/anot-pro/ref-5753.htm)
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*Topic: Encyclopedia › Life and health › Microorganisms and fungi › Other microbial eukaryotes › Other heterotrophic and fungal-like protists › Slime molds › Protosteloid and other slime mold lineages*
*Initially written Sep 17, 2026 · Reviewed: Oct 21, 2026 · Edited: Oct 11, 2026; Oct 15, 2026; Oct 21, 2026 · Last review: Oct 21, 2026*
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License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license