Holozoa

Holozoans Temporal range: Ediacaran - Present, 610–0 Ma PreЄ Є O S D C P T J K Pg N
Orange elephant ear sponge, Agelas clathrodes, in foreground. Two corals in the background: a sea fan, Iciligorgia schrammi, and a sea rod, Plexaurella nutans.
Scientific classification
Domain:	Eukaryota
(unranked):	Unikonta
(unranked):	Opisthokonta
(unranked):	Holozoa Lang et al. 2002
Subgroups
Ichthyosporea (= Mesomycetozoea) Choanoflagellata Metazoa (animals)

Holozoa is a group of organisms that includes animals and their closest single-celled relatives, but excludes fungi.^[1][2][3][4] Holozoa is also an old name for the tunicate genus Distaplia.^[5]

Because Holozoa is a clade including all organisms more closely related to animals than to fungi, some authors prefer it to recognizing paraphyletic groups such as Choanozoa, which mostly consists of Holozoa minus animals.^[6]

Perhaps the best-known holozoans, apart from animals, are the choanoflagellates, which strongly resemble the collar cells of sponges, and so were theorized to be related to sponges even in the 19th century. Proterospongia is an example of a colonial choanoflagellate that may shed light on the origin of sponges.

The affinities of the other single-celled holozoans only began to be recognized in the 1990s.^[7] A group of mostly parasitic species called Icthyosporea or Mesomycetozoea is sometimes grouped with other species in Mesomycetozoa (note the difference in the ending). The amoeboid genera Ministeria and Capsaspora may be united in a group called Filasterea by the structure of their thread-like pseudopods. Along with choanoflagellates, filastereans may be closely related to animals, and one analysis grouped them together as the clade Filozoa.^[3]

Fossil record

The oldest fossils of holozoans are animals, which date back to the Ediacaran period, about 600 million years ago.^[8]

Cladogram

The most up to date cladogram is^[9][10]

Opisthokonta	Holomycota Fungi Discicristoidea Nucleariida Fonticulida Holozoa Mesomycetozoa Corallochytrium Filozoa Filasterea Choanoflagellatea Animalia

References

1. Aleshin VV, Konstantinova AV, Mikhailov KV, Nikitin MA, Petrov NB (December 2007). "Do we need many genes for phylogenetic inference?". Biochemistry Mosc. 72 (12): 1313–23. doi:10.1134/S000629790712005X. PMID 18205615.
2. Lang BF, O'Kelly C, Nerad T, Gray MW, Burger G (October 2002). "The closest unicellular relatives of animals". Curr. Biol. 12 (20): 1773–8. doi:10.1016/S0960-9822(02)01187-9. PMID 12401173.
3. Shalchian-Tabrizi, Kamran; Minge, Marianne A.; Espelund, Mari; Orr, Russell; Ruden, Torgeir; Jakobsen, Kjetill S.; Cavalier-Smith, Thomas; Aramayo, Rodolfo (2008). Aramayo, Rodolfo, ed. "Multigene phylogeny of choanozoa and the origin of animals". PLoS ONE 3 (5): e2098. doi:10.1371/journal.pone.0002098. PMC 2346548. PMID 18461162.
4. Elias M, Archibald JM (August 2009). "The RJL family of small GTPases is an ancient eukaryotic invention probably functionally associated with the flagellar apparatus". Gene 442 (1–2): 63–72. doi:10.1016/j.gene.2009.04.011. PMID 19393304.
5. Tatiàn, Marcos; Antacli, Julieta Maria; Sahade, Ricardo (2005). "Ascidians (Tunicata, Ascidiacea): species distribution along the Scotia Arc". Scientia Marina 69 (suppl. 2): 205–214.
6. Steenkamp, Emma T.; Wright, Jane; Baldauf, Sandra L. (2006). "The Protistan Origins of Animals and Fungi". Molecular Biology & Evolution 23 (1): 93–106. doi:10.1093/molbev/msj011. PMID 16151185.
7. Ragan, Mark A.; Goggin, C. Louise; Cawthorn, Richard J.; Cerenius, Lage; Jamieson, Angela V.C.; Plourde, Susan M.; Rand, Thomas G.; Söoderhäll, Kenneth; Gutell, Robin R. (1996). "A novel clade of protistan parasites near the animal-fungal divergence". PNAS 93 (21): 11907–11912. doi:10.1073/pnas.93.21.11907. PMC 38157. PMID 8876236.
8. Porter, Suzannah M. (2004). "The fossil record of early eukaryotic diversification". Paleontological Society Papers 10: 35–50.
9. Parfrey, Laura Wegener; Lahr, Daniel J. G.; Knoll, Andrew H.; Katz, Laura A. (2011-08-16). "Estimating the timing of early eukaryotic diversification with multigene molecular clocks". Proceedings of the National Academy of Sciences 108 (33): 13624–13629. doi:10.1073/pnas.1110633108. ISSN 0027-8424. PMC 3158185. PMID 21810989.
10. Torruella, Guifré; de Mendoza, Alex; Grau-Bové, Xavier; Antó, Meritxell; Chaplin, Mark A.; del Campo, Javier; Eme, Laura; Pérez-Cordón, Gregorio; Whipps, Christopher M. "Phylogenomics Reveals Convergent Evolution of Lifestyles in Close Relatives of Animals and Fungi". Current Biology 25 (18): 2404–2410. doi:10.1016/j.cub.2015.07.053. ISSN 0960-9822.