Chlorophyta is a division of green algae informally called chlorophytes.
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.
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.
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.
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.
Ochrophytes, also known as heterokontophytes or stramenochromes, are a group of algae. They are the photosynthetic stramenopiles, a group of eukaryotes, organisms with a cell nucleus, characterized by the presence of two unequal flagella, one of which has tripartite hairs called mastigonemes. In particular, they are characterized by photosynthetic organelles or plastids enclosed by four membranes, with membrane-bound compartments called thylakoids organized in piles of three, chlorophyll a and c as their photosynthetic pigments, and additional pigments such as β-carotene and xanthophylls. Ochrophytes are one of the most diverse lineages of eukaryotes, containing ecologically important algae such as brown algae and diatoms. They are classified either as phylum Ochrophyta or Heterokontophyta, or as subphylum Ochrophytina within phylum Gyrista. Their plastids are of red algal origin.
The Urmetazoan is the hypothetical last common ancestor of all animals, or metazoans. It is universally accepted to be a multicellular heterotroph — with the novelties of a germline and oogamy, an extracellular matrix (ECM) and basement membrane, cell-cell and cell-ECM adhesions and signaling pathways, collagen IV and fibrillar collagen, different cell types, spatial regulation and a complex developmental plan, and relegated unicellular stages.
Planulozoa is a clade which includes the Placozoa, Cnidaria and the Bilateria. 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. The clade excludes basal animals such as the Ctenophora, and Porifera (sponges). Although this clade was sometimes used to specify a clade of Cnidaria and Bilateria to the exclusion of Placozoa, this is no longer favoured due to recent data indicating a sister group relationship between Cnidaria and Placozoa, another study still supports Placozoa as sister to Cnidaria+Bilateria.
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.
E-Z827, also known as E1b1b1b, is a major human Y-chromosome DNA haplogroup. It is the parent lineage to the E-Z830 and E-V257 subclades, and defines their common phylogeny. The former is predominantly found in the Middle East; the latter is most frequently observed in North Africa, with its E-M81 subclade observed among the ancient Guanche natives of the Canary Islands. E-Z827 is also found at lower frequencies in Europe, and in isolated parts of Southeast Africa.
ParaHoxozoa is a clade of animals that consists of Bilateria, Placozoa, and Cnidaria.
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.
Polyplacotoma mediterranea is a species in the phylum Placozoa, only representative of the genus Polyplacotoma. They differ greatly from other species of placozoans with regards to their morphology and genetic makeup, and have been ranked in the separate class Polyplacotomia. P. mediterranea has the smallest mitogenome, the lowest GC content, and the smallest intergenic spacer regions of all placozoans. Their bodily structure consists of elongated polytomous body branches, as well as a maximum size that is greater than 10 mm in length. The mitochondrial genome of Polyplacotoma mediterranea is also very compact and contains overlapping protein and tRNA gene codes.
Uniplacotomia is a class of placozoans encompassing the vast majority of the phylum, with the exception of Polyplacotoma. It was established in 2022. It comprises the orders Trichoplacea, Cladhexea and Hoilungea. Their morphology is consistent across the class, resembling the typical Trichoplax as mostly rounded, flat organisms rather than the polytomous, branching structure exhibited by Polyplacotomia.
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.
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.
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.
Maculicorpus is a genus of fossil placozoan from the Middle Triassic of Germany, and the first placozoan known from the fossil record. It comprises a single known species, Maculicorpus microbialis.
