Capsaspora is a monotypic genus containing the single species Capsaspora owczarzaki, a single-celled eukaryote which is a symbiont in the haemolymph of the tropical freshwater snail Biomphalaria glabrata. The genome of C. owczarzaki has been sequenced.
C. owczarzaki cells were described as 3 to 5 μm amoebas with a nucleus ⅓ - ½ of thediameter of the cell (containing a central nucleolus), long unbranched pseudopodia, mitochondria with flattened cristae, numerous phagosomes, lipid vacuoles, glycogen granules and a Golgi apparatus. Cells could encyst in response to crowding, generating 4 to 5 μm cysts with a double wall: the outer thin, irregular and loosely attached; and the inner thicker, smooth.
C. owczarzaki is together with Ministeria vibrans a member of the Filasterea clade. This group is probably the sister group to a clade comprising Metazoa and Choanoflagellata, which together form the Filozoa  (See Figure 1).
C. owczarzaki is of scientific interest because it is one of the closest unicellular relatives of multicellular animals. Its genome has recently been sequenced and shows several genes involved in metazoan multicellularity, such as integrins, metazoan transcription factors, and protein tyrosine kinases. Moreover, it has relevance to human health because its host, the snail Biomphalaria glabrata, is also the intermediate host of the digenean flatworm Schistosoma mansoni, the causative agent of widespread schistosomiasis in humans. C. owczarzaki not only parasitizes the intermediate host of S. mansoni but also attacks and kills the sporocysts of the flatworm living inside the snail.
- Hertel L. A., Bayne, C. J. & Loke, E. S. (2002), "The symbiont Capsaspora owczarzaki, nov. gen. nov. sp., isolated from three strains of the pulmonate snail Biomphalaria glabrata is related to members of the Mesomycetozoea", International Journal for Parasitology 32 (9): 1183, doi:10.1016/S0020-7519(02)00066-8, PMID 12117501
- Stibbs HH, Owczarzak A, Bayne CJ, DeWan P. (1979) Schistosomesporocyst-killing amoebae isolated from Biomphalaria glabrata. J Invertebr Pathol 33(2): 159-70
- Owczarzak A, Stibbs HH, Bayne CJ. (1980) The destruction of Schistosoma mansoni mother sporocystsin vitro by amoebae isolated from Biomphalaria glabrata: an ultrastructuralstudy. J. Invertebr. Pathol. 35, 26–33
- Sebe-PedrosA. 2013. The origin of metazoan multicellularity, a genomic and functionalapproach. PhD UB, Facultat de Biologia, Departament de Genètica
- Torruella G, Derelle R, Paps J, Lang F, Roger A, Shalchian-Tabrizi K, Ruiz-Trillo I. (2012) Phylogenetic relationships within theOpisthokonta based on phylogenomic analyses of conserved single copy proteindomains. Molecular Biology and Evolution 29(2): 531-544.
- Shalchian-Tabrizi K, Minge MA, Espelund M, Orr R, Ruden T, Jakobsen KS,Cavalier-Smith T. (2008)Multigene phylogeny of choanozoa and the origin of animals. PLoS One 3(5):e2098
- Paps J, Medina-Chacon L, Marshall W, Suga H, Ruiz-Trillo I. (2013) Molecular phylogeny of Unikonts: new insightsinto the position of apusomonads and ancyromonads and the internalrelationships of opisthokonts. Protist 164(1): 2-12
- Sebe-Pedros A, RogerA, Lang F, King N, Ruiz-Trillo I. (2010) Ancient origin of integrin-mediated adhesion and signaling machinery. Proceedings National Academic of Sciences USA107(22): 10142-7
- Sebe-Pedros A, de Mendoza A, Lang F, Degnan B, Ruiz-Trillo I. (2011) Unexpected repertoire of metazoan transcription factors in the unicellular holozoan Capsaspora owczarzaki. Molecular Biology and Evolution 28(3): 1241-54
- Suga H, DacreM, de Mendoza A,Shalchian-Tabrizi K, Manning G, Ruiz-TrilloI. (2012) Genomic Survey of Premetazoans Shows Deep Conservation of Cytoplasmic Tyrosine Kinases and Multiple Radiations of Receptor Tyrosine Kinases. Science Signaling 5(222),ra35[DOI: 10.1126/scisignal.2002733]