Planulozoa

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Planulozoa
Temporal range: Ediacaran–Recent
Animalia diversity.jpg
Diversity of planulozoans
Scientific classification
Kingdom:
Subkingdom:
(unranked):
(unranked):
Planulozoa

Wallberg et al., 2004
Phyla

Bilateria / Triploblasts (unranked)?

Planulozoa is a clade which includes the Placozoa, Cnidaria (corals and jellyfish) and the Bilateria (all the more complex animals including worms, insects and vertebrates). [2] [3] The designation Planulozoa may be considered a synonym to Parahoxozoa. Within Planulozoa, the Placozoa may be a sister of Cnidaria to the exclusion of Bilateria. [4] [5] [6] [7] The clade excludes basal animals such as the Ctenophora (comb jellies), [8] [9] [3] and Porifera (sponges). [10] [11] [12] Although this clade was sometimes used to specify a clade of Cnidaria and Bilateria to the exclusion of Placozoa (against the original intention of its proposal), this is no longer favoured due to recent data indicating a sister group relationship between Cnidaria and Placozoa, [13] another study still supports Placozoa as sister to Cnidaria+Bilateria. [14]

The phylogenetic tree indicates approximately how many millions of years ago (mya) the lineages split. Here, Planulozoa is shown sans Placozoa. [15] [16] [17]

Planulozoa are associated with the emergence of the Zoc and ZF-NC gene domains. [18]


Choanozoa
950 mya

Related Research Articles

<span class="mw-page-title-main">Cnidaria</span> Aquatic animal phylum having cnydocytes

Cnidaria is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in fresh water and marine environments, including jellyfish, hydroids, sea anemones, corals and some of the smallest marine parasites. Their distinguishing features are a decentralized nervous system distributed throughout a gelatinous body and the presence of cnidocytes or cnidoblasts, specialized cells with ejectable flagella used mainly for envenomation and capturing prey. Their bodies consist of mesoglea, a non-living, jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. Cnidarians are also some of the only animals that can reproduce both sexually and asexually.

<span class="mw-page-title-main">Placozoa</span> Basal form of free-living invertebrate

Placozoa is a phylum of marine and free-living (non-parasitic) animals. They are blob-like animals composed of aggregations of cells. Moving in water by ciliary motion, eating food by engulfment, reproducing by fission or budding, placozoans are described as "the simplest animals on Earth." Structural and molecular analyses have supported them as among the most basal animals, thus, constituting a primitive metazoan phylum.

<span class="mw-page-title-main">Bilateria</span> Animals with embryonic bilateral symmetry

Bilateria is a large clade or infrakingdom of animals called bilaterians, characterized by bilateral symmetry during embryonic development. This means their body plans are laid around a longitudinal axis with a front and a rear end, as well as a left–right–symmetrical belly (ventral) and back (dorsal) surface. Nearly all bilaterians maintain a bilaterally symmetrical body as adults; the most notable exception is the echinoderms, which extend to pentaradial symmetry as adults, but are only bilaterally symmetrical as an embryo. Cephalization is also a characteristic feature among most bilaterians, where the special sense organs and central nerve ganglia become concentrated at the front/rostral end.

<span class="mw-page-title-main">Ctenophora</span> Phylum of gelatinous marine animals

Ctenophora comprise a phylum of marine invertebrates, commonly known as comb jellies, that inhabit sea waters worldwide. They are notable for the groups of cilia they use for swimming, and they are the largest animals to swim with the help of cilia.

<span class="mw-page-title-main">Ecdysozoa</span> Superphylum of protostomes including arthropods, nematodes and others

Ecdysozoa is a group of protostome animals, including Arthropoda, Nematoda, and several smaller phyla. The grouping of these animal phyla into a single clade was first proposed by Eernisse et al. (1992) based on a phylogenetic analysis of 141 morphological characters of ultrastructural and embryological phenotypes. This clade, that is, a group consisting of a common ancestor and all its descendants, was formally named by Aguinaldo et al. in 1997, based mainly on phylogenetic trees constructed using 18S ribosomal RNA genes.

<span class="mw-page-title-main">Parazoa</span> Ancestral subkingdom of animals

Parazoa are a taxon with sub-kingdom category that is located at the base of the phylogenetic tree of the animal kingdom in opposition to the sub-kingdom Eumetazoa; they group together the most primitive forms, characterized by not having proper tissues or that, in any case, these tissues are only partially differentiated. They generally group a single phylum, Porifera, which lack muscles, nerves and internal organs, which in many cases resembles a cell colony rather than a multicellular organism itself. All other animals are eumetazoans, which do have differentiated tissues.

<span class="mw-page-title-main">Eumetazoa</span> Basal animal clade as a sister group of the Porifera

Eumetazoa, also known as diploblasts, Epitheliozoa or Histozoa, are a proposed basal animal clade as a sister group of Porifera (sponges). The basal eumetazoan clades are the Ctenophora and the ParaHoxozoa. Placozoa is now also seen as a eumetazoan in the ParaHoxozoa. The competing hypothesis is the Myriazoa clade.

<span class="mw-page-title-main">Nerve net</span> Nervous systems lacking a brain

A nerve net consists of interconnected neurons lacking a brain or any form of cephalization. While organisms with bilateral body symmetry are normally associated with a condensation of neurons or, in more advanced forms, a central nervous system, organisms with radial symmetry are associated with nerve nets, and are found in members of the Ctenophora, Cnidaria, and Echinodermata phyla, all of which are found in marine environments. In the Xenacoelomorpha, a phylum of bilaterally symmetrical animals, members of the subphylum Xenoturbellida also possess a nerve net. Nerve nets can provide animals with the ability to sense objects through the use of the sensory neurons within the nerve net.

<i>Trichoplax</i> Genus of Placozoa

Trichoplax adhaerens is one of the four named species in the phylum Placozoa. The others are Hoilungia hongkongensis, Polyplacotoma mediterranea and Cladtertia collaboinventa. Placozoa is a basal group of multicellular animals, possible relatives of Cnidaria. Trichoplax are very flat organisms commonly less than 4 mm in diameter, lacking any organs or internal structures. They have two cellular layers: the top epitheloid layer is made of ciliated "cover cells" flattened toward the outside of the organism, and the bottom layer is made up of cylinder cells that possess cilia used in locomotion, and gland cells that lack cilia. Between these layers is the fibre syncytium, a liquid-filled cavity strutted open by star-like fibres.

<span class="mw-page-title-main">Radiata</span> Taxonomic rank that has been used to classify radially symmetric animals

Radiata or Radiates is a historical taxonomic rank that was used to classify animals with radially symmetric body plans. The term Radiata is no longer accepted, as it united several different groupings of animals that do not form a monophyletic group under current views of animal phylogeny. The similarities once offered in justification of the taxon, such as radial symmetry, are now taken to be the result of either incorrect evaluations by early researchers or convergent evolution, rather than an indication of a common ancestor. Because of this, the term is used mostly in a historical context.

<span class="mw-page-title-main">Coelenterata</span> Term encompassing animal phyla Cnidaria and Ctenophora

Coelenterata is a term encompassing the animal phyla Cnidaria and Ctenophora. The name comes from Ancient Greek κοῖλος (koîlos) 'hollow' and ἔντερον (énteron) 'intestine', referring to the hollow body cavity common to these two phyla. They have very simple tissue organization, with only two layers of cells, along with a middle undifferentiated layer called mesoglea, and radial symmetry. Some examples are corals, which are typically colonial; hydrae, jellyfish, sea anemones, and Aurelia, which are solitary; Pennatula; Portuguese man o' war; Gorgonia; and Physalia. Coelenterata lack a specialized circulatory system, relying instead on diffusion across the tissue layers.

<span class="mw-page-title-main">Acoela</span> Order of flatworm-like bilaterian animals

Acoela, or the acoels, is an order of small and simple invertebrates in the subphylum Acoelomorpha of phylum Xenacoelomorpha, a deep branching bilaterian group of animals, which resemble flatworms. Historically they were treated as an order of turbellarian flatworms. About 400 species are known, but probably many more not yet described.

<span class="mw-page-title-main">Animal</span> Kingdom of living things

Animals are multicellular, eukaryotic organisms in the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, have myocytes and are able to move, can reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. Animals form a clade, meaning that they arose from a single common ancestor.

The urbilaterian is the hypothetical last common ancestor of the bilaterian clade, i.e., all animals having a bilateral symmetry.

<span class="mw-page-title-main">Protostome</span> Clade of animals whose mouth develops before the anus

Protostomia is the clade of animals once thought to be characterized by the formation of the organism's mouth before its anus during embryonic development. This nature has since been discovered to be extremely variable among Protostomia's members, although the reverse is typically true of its sister clade, Deuterostomia. Well known examples of protostomes are arthropods, molluscs, annelids, flatworms and nematodes. They are also called schizocoelomates since schizocoely typically occurs in them.

<span class="mw-page-title-main">Holozoa</span> Clade containing animals and some protists

Holozoa is a clade of organisms that includes animals and their closest single-celled relatives, but excludes fungi and all other organisms. Together they amount to more than 1.5 million species of purely heterotrophic organisms, including around 300 unicellular species. It consists of various subgroups, namely Metazoa and the protists Choanoflagellata, Filasterea, Pluriformea and Ichthyosporea. Along with fungi and some other groups, Holozoa is part of the Opisthokonta, a supergroup of eukaryotes. Choanofila was previously used as the name for a group similar in composition to Holozoa, but its usage is discouraged now because it excludes animals and is therefore paraphyletic.

<span class="mw-page-title-main">Spiralia</span> Clade of protosomes with spiral cleavage during early development

The Spiralia are a morphologically diverse clade of protostome animals, including within their number the molluscs, annelids, platyhelminths and other taxa. The term Spiralia is applied to those phyla that exhibit canonical spiral cleavage, a pattern of early development found in most members of the Lophotrochozoa.

<span class="mw-page-title-main">ParaHoxozoa</span> Clade of all animals except sponges and comb jellies

ParaHoxozoa is a clade of animals that consists of Bilateria, Placozoa, and Cnidaria. The relationship of this clade relative to the two other animal lineages Ctenophora and Porifera is debated. Some phylogenomic studies have presented evidence supporting Ctenophora as the sister to Parahoxozoa and Porifera as the sister group to the rest of animals. Other studies have presented evidence supporting Porifera as the sister to Parahoxozoa and Ctenophora as the sister group to the rest of animals, finding that nervous systems either evolved independently in ctenophores and parahoxozoans, or were secondarily lost in poriferans. If ctenophores are taken to have diverged first, Eumetazoa is sometimes used as a synonym for ParaHoxozoa.

<span class="mw-page-title-main">Choanozoa</span> Clade of opisthokont eukaryotes consisting of the choanoflagellates and the animals

Choanozoa is a clade of opisthokont eukaryotes consisting of the choanoflagellates (Choanoflagellatea) and the animals. The sister-group relationship between the choanoflagellates and animals has important implications for the origin of the animals. The clade was identified in 2015 by Graham Budd and Sören Jensen, who used the name Apoikozoa. The 2018 revision of the classification first proposed by the International Society of Protistologists in 2012 recommends the use of the name Choanozoa.

<i>Cladtertia</i> Genus of placozoans

Cladtertia is a genus of placozoan discovered in 2022, whose only currently described species is Cladtertia collaboinventa. However, the genus is known to contain several other species, awaiting a formal description. Its closest described relative is Hoilungia hongkongensis, with whom it forms the order Hoilungea. After Trichoplax, Hoilungia and Polyplacotomia, it is the fourth extant placozoan genus to be described.

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