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| Cladhexea | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Placozoa |
| Class: | Uniplacotomia |
| Order: | Cladhexea Tessler et al., 2022 [1] |
Cladhexea is a recently created placozoan order comprising yet-undescribed species. Named in 2022, it is believed to be sister to Hoilungea, and corresponds to Clade VI of the literature. [1]
The name comes from Ancient Greek kládos (clade) and hexa (six), referring to its specimens previously being assigned to placozoan Clade VI in literature.
In biological phylogenetics, a clade, also known as a monophyletic group or natural group, is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. In the taxonomical literature, sometimes the Latin form cladus is used rather than the English form. Clades are the fundamental unit of cladistics, a modern approach to taxonomy adopted by most biological fields.
In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of taxa which meets these criteria:
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.
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.
Triploblasty is a condition of the gastrula in which there are three primary germ layers: the ectoderm, mesoderm, and endoderm. Germ cells are set aside in the embryo at the blastula stage, and are incorporated into the gonads during organogenesis. The germ layers form during the gastrulation of the blastula. The term triploblast may refer to any egg cell in which the blastoderm splits into three layers.
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.
Ginkgo is a genus of non-flowering seed plants. The scientific name is also used as the English name. The order to which it belongs, Ginkgoales, first appeared in the Permian, 270 million years ago, and Ginkgo is now the only living genus within the order. The rate of evolution within the genus has been slow, and almost all its species had become extinct by the end of the Pliocene. The sole surviving species, Ginkgo biloba, is found in the wild only in China, but is cultivated around the world. The relationships between ginkgos and other groups of plants are not fully resolved.
Euskelia is a proposed clade of extinct temnospondyl amphibians. The naming derives from the ancient Greek eu, meaning "true", and skelos, meaning "limb", in reference to well-ossified limb bones with crests to which muscles were attached. Members of this group have the most ossified skeleton of all temnospondyls.
Lichinales is the sole order of ascomycete fungi in the class Lichinomycetes. It contains three families: Gloeoheppiaceae, Lichinaceae, and Peltulaceae. Most species are lichenized. Lichinales was proposed in 1986 by German lichenologists Aino Henssen and Burkhard Büdel. The class Lichinomycetes was created by Valérie Reeb, François Lutzoni and Claude Roux in 2004.
Neritimorpha is a clade of gastropod molluscs that contains around 2,000 extant species of sea snails, limpets, freshwater snails, land snails and slugs. This clade used to be known as the superorder Neritopsina.
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.
Scrotifera is a clade of placental mammals that groups together grandorder Ferungulata, Chiroptera (bats), other extinct members and their common ancestors. The clade Scrotifera is a sister group to the order Eulipotyphla based on evidence from molecular phylogenetics, and together they make superorder Laurasiatheria. The last common ancestor of Scrotifera is supposed to have diversified ca. 73.1 to 85.5 million years ago.
Archaeopterodactyloidea is an extinct clade of pterodactyloid pterosaurs that lived from the middle Late Jurassic to the latest Early Cretaceous periods of Africa, Asia, Europe and North America. It was named by Alexander Wilhelm Armin Kellner in 1996 as the group that contains Germanodactylus, Pterodactylus, the Ctenochasmatidae and the Gallodactylidae. In 2003, Kellner defined the clade as a node-based taxon consisting of the last common ancestor of Pterodactylus, Ctenochasma and Gallodactylus and all its descendants. Although phylogenetic analyses that based on David Unwin's 2003 analysis do not recover monophyletic Archaeopterodactyloidea, phylogenetic analyses that based on Kellner's analyses, or the analyses of Brian Andres recover monophyletic Archaeopterodactyloidea at the base of the Pterodactyloidea.
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.
Hoilungia is a genus that contains one of the simplest animals and belongs to the phylum Placozoa. Described in 2018, it has only one named species, H. hongkongensis, although there are possible other species. The animal superficially resembles another placozoan, Trichoplax adhaerens, but genetically distinct from it as mitochondrial DNA analysis revealed.
Ortygornis is a genus of birds in the francolin group of the family Phasianidae.
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.
Hoilungea is a recently created placozoan order comprising Cladtertia, Hoilungia, and other yet-undescribed species. Named in 2022, it is believed to be sister to Cladhexea, and corresponds to Clades III, IV, V and VII of the literature.
Polyplacotomia is a class of placozoans, to this date only comprising Polyplacotoma mediterranea. It was established in 2022. Their morphology is strikingly different from other placozoans in Uniplacotomia, exhibiting a highly ramified, branching structure with multiple amoeboid projections. It differs from Uniplacotomia by 76 uniquely present and 600 absent genes.
Hoilungidae is a recently created placozoan family comprising Hoilungia and other yet-undescribed species. Named in 2022, it is believed to be sister to Cladtertiidae, and corresponds to Clades IV, V and VII of the literature.
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