The Mesomycetozoea (or DRIP clade, or Ichthyosporea) are a small group of protists, mostly parasites of fish and other animals.
They are not particularly distinctive morphologically, appearing in host tissues as enlarged spheres or ovals containing spores, and most were originally classified in various groups as fungi, protozoa, or colorless algae. However, they form a coherent group on molecular trees, closely related to both animals and fungi and so of interest to biologists studying their origins. In a 2008 study they emerge robustly as the sister-group of the clade Filozoa, which includes the animals.
Huldtgren et al., following x-ray tomography of microfossils of the Ediacaran Doushantuo Formation, has interpreted them as mesomycetozoan spore capsules.
The name DRIP is an acronym for the first protozoa identified as members of the group,  Cavalier-Smith later treated them as the class Ichthyosporea, since they were all parasites of fish.
Since other new members have been added (e.g. the former fungal orders Eccrinales and Amoebidiales), Mendoza et al. suggested changing the name to Mesomycetozoea, which refers to their evolutionary position. Note the name Mesomycetozoa (without a second e) is also used to refer to this group, but Mendoza et al. use it as an alternate name for the phylum Choanozoa.
Eukaryota tree. Note "Ichthyosporea" at bottom left, in Opisthokont
clade. "Metazoa" are animals, and Choanoflagellates
are closely aligned. Fungi is at other end of Opisthokont clade, with Cristidiscoidea
closely aligned. Ichthyosporea is in the middle ("Meso-") of the fungi ("-myceto-") and the animals ("-zoea").
- ^ Shalchian-Tabrizi K., Minge M.A., Espelund M. et al. (2008). Aramayo, Rodolfo, ed. "Multigene Phylogeny of Choanozoa and the Origin of Animals". PLoS ONE 3 (5): e2098. PMC 2346548. PMID 18461162. doi:10.1371/journal.pone.0002098.
- ^ Douglas Fox, "How life got complicated", Discover Magazine, December 2012.
- ^ Ragan MA, Goggin CL, Cawthorn RJ et al. (October 1996). "A novel clade of protistan parasites near the animal-fungal divergence". Proc. Natl. Acad. Sci. U.S.A. 93 (21): 11907–12. PMC 38157. PMID 8876236. doi:10.1073/pnas.93.21.11907.
- ^ Herr RA, Ajello L, Taylor JW, Arseculeratne SN, Mendoza L (September 1999). "Phylogenetic Analysis of Rhinosporidium seeberi's 18S Small-Subunit Ribosomal DNA Groups This Pathogen among Members of the Protoctistan Mesomycetozoa Clade". J. Clin. Microbiol. 37 (9): 2750–4. PMC 85368. PMID 10449446.
- ^ Mendoza L, Taylor JW, Ajello L (2002). "The class mesomycetozoea: a heterogeneous group of microorganisms at the animal-fungal boundary". Annu. Rev. Microbiol. 56: 315–44. PMID 12142489. doi:10.1146/annurev.micro.56.012302.160950.