They are not particularly distinctive morphologically, appearing in host tissues as enlarged spheres or ovals containingspores, 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 bothanimals andfungi and so of interest to biologists studying their origins. In a 2008 study they emerge robustly as the sibling-group of thecladeFilozoa, which includes the animals.[2][3]
The name DRIP is an acronym for the first protozoa identified as members of the group,[5]Cavalier-Smith later treated them as the classIchthyosporea, since they were all parasites of fish.
Since other new members have been added (e.g. the former fungal ordersEccrinales andAmoebidiales), Mendozaet al. suggested changing the name to Mesomycetozoea, which refers to their evolutionary position. On Eukaryota tree, inOpisthokont clade, Mesomycetozoea is in the middle ("Meso-") of the fungi ("-myceto-") and the animals ("-zoea").[6] The name Mesomycetozoa (without a third e) is also used to refer to this group, but Mendozaet al. use it as an alternate name for basal Opisthokonts.[7]
Eukaryota tree. Note "Ichthyosporea" at bottom left, inOpisthokont clade. "Metazoa" are animals, andChoanoflagellates are closely aligned. Fungi is at other end of Opisthokont clade, withCristidiscoidea closely aligned. Ichthyosporea is in the middle ("Meso-") of the fungi ("-myceto-") and the animals ("-zoea").
^Cavalier-Smith, T. 1998. Neomonada and the origin of animals and fungi. In: Coombs GH, Vickerman K, Sleigh MA, Warren A (ed.)Evolutionary relationships among protozoa. Kluwer, London, pp. 375-407,
^Mendoza L, Taylor JW, Ajello L (October 2002). "The class mesomycetozoea: a heterogeneous group of microorganisms at the animal-fungal boundary".Annu. Rev. Microbiol.56:315–44.doi:10.1146/annurev.micro.56.012302.160950.PMID12142489.
^Borteiro, Claudio; Baldo, Diego; Maronna, Maximiliano Manuel; Ubilla (2018). "Amphibian parasites of the Order Dermocystida (Ichthyosporea): current knowledge, taxonomic review and new records from Brazil".Zootaxa.4461 (4):499–518.doi:10.11646/zootaxa.4461.4.3.hdl:11336/84098.PMID30314064.S2CID52977120.
^Cavalier-Smith (May 2012). "Early evolution of eukaryote feeding modes, cell structural diversity, and classification of the protozoan phyla Loukozoa, Sulcozoa, and Choanozoa".European Journal of Protistology.49 (2):115–178.doi:10.1016/j.ejop.2012.06.001.PMID23085100.
