Holozoa

Composition Holozoa is a clade that includes animals and their closest relatives, as well as their common ancestor, but excludes fungi. It is defined on a branch-based approach as the clade encompassing all relatives of Homo sapiens (an animal), but not Neurospora crassa (a fungus). • Ichthyosporea, also known as Mesomycetozoea and comprising around 40 species, largely consist of parasites or commensals. They interact with a diverse range of animals, from humans and fish to marine invertebrates. Most reproduce through multinucleated colonies and disperse as flagellates or amoebae. They are characterized by a blastula phase during their embryonic development and, except for the amorphous sponges, the formation of germ layers and differentiated tissues. == Evolution ==

Phylogeny Holozoa, along with a clade that contains fungi and their protist relatives (Holomycota), are part of the larger supergroup of eukaryotes known as Opisthokonta. Holozoa diverged from their opisthokont ancestor around 1070 million years ago (Mya). The choanoflagellates, animals and filastereans group together as the clade Filozoa. Within Filozoa, the choanoflagellates and animals group together as the clade Choanozoa. Alternatively, Ichthyosporea may be the earliest-branching of the two, while Pluriformea is sister to the Filozoa clade comprising filastereans, choanoflagellates and animals. This second outcome is more strongly supported after the discovery of Syssomonas. Unicellular ancestry of animals , but they display developmental processes using similar molecules. An actomyosin network controls the cellularization of both an ichthyosporean coenocyte (A) and a fruit fly blastoderm (B). Similarly, actomyosin contraction allows both the shaping of choanoflagellate colonies (C) and the gastrulation of animal embryos. The quest to elucidate the evolutionary origins of animals from a unicellular ancestor requires an examination of the transition to multicellularity. In the absence of a fossil record documenting this evolution, insights into the unicellular ancestor of animals are obtained from the analysis of shared genes and genetic pathways between animals and their closest living unicellular relatives. The genetic content of these single-celled holozoans has revealed a significant discovery: many genetic characteristics previously thought as unique to animals can also be found in these unicellular relatives. This suggests that the origin of multicellular animals did not happen solely because of the appearance of new genes (i.e. innovation), but because of pre-existing genes that were adapted or utilized in new ways (i.e. co-option). was the method of dispersal and propagation. == Taxonomy ==

History Prior to 2002, a relationship between Choanoflagellata, Ichthyosporea and the animal-fungi divergence was considered on the basis of morphology and ultrastructure. Early phylogenetic analyses gave contradicting results, because the amount of available DNA sequences was insufficient to yield unambiguous results. The taxonomic uncertainty was such that, for example, some Ichthyosporea were traditionally treated as trichomycete fungi. and 2017 This classification excludes animals, even though they descend from the same common ancestor as choanofilan protists, making it a paraphyletic group rather than a true clade. Modern cladistic approaches to eukaryotic classification prioritise monophyletic groupings over traditional ranks, which are increasingly perceived as redundant and superfluous. Because Holozoa is a clade, its use is preferred over the paraphyletic taxon Choanofila. • Holozoa • Incertae sedis: Bicellum brasieri • Tunicaraptor • Ichthyosporea [Mesomycetozoea ] • Dermocystida • Ichthyophonida • Pluriformea • Corallochytrium • Syssomonas • Filozoa • Filasterea • Capsaspora • Ministeria • Pigoraptor • Txikispora • Choanozoa [Choanozoa (P)] • Choanoflagellata [Choanoflagellatea ] • Craspedida • Acanthoecida • Metazoa [Animalia ] • Porifera • Placozoa • Ctenophora • Cnidaria • Bilateria ==Notes==