The Lophophorata or Tentaculata are a Lophotrochozoan clade consisting of the Brachiozoa and the Bryozoa. They have a lophophore. Molecular phylogenetic analyses suggest that lophophorates are protostomes, but on morphological grounds they have been assessed as deuterostomes. Fossil finds of the "tommotiid" Wufengella suggest that they evolved from worm-like animals that resembled annelids.
The Mesozoa are minuscule, worm-like parasites of marine invertebrates. Generally, these tiny, elusive creatures consist of a somatoderm of ciliated cells surrounding one or more reproductive cells.
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.
The Trochozoa are a proposed Lophotrochozoa clade that is a sister clade of Bryozoa. The clade would include animals in six phyla: the Nemertea, the Annelida, the Cycliophora, the Mollusca, and the two Brachiozoan phyla, Brachiopoda and Phoronida.
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.
Orthonectida is a small phylum of poorly known parasites of marine invertebrates that are among the simplest of multi-cellular organisms. Members of this phylum are known as orthonectids.
Lophotrochozoa is a clade of protostome animals within the Spiralia. The taxon was established as a monophyletic group based on molecular evidence. The clade includes animals like annelids, molluscs, bryozoans, brachiopods, and platyhelminthes.
Acoelomorpha is a subphylum of very simple and small soft-bodied animals with planula-like features which live in marine or brackish waters. They usually live between grains of sediment, swimming as plankton, or crawling on other organisms, such as algae and corals. With the exception of two acoel freshwater species, all known acoelomorphs are marine.
Dicyemida, also known as Rhombozoa, is a phylum of tiny parasites that live in the renal appendages of cephalopods.
The lophophore is a characteristic feeding organ possessed by four major groups of animals: the Brachiopoda, Bryozoa, Hyolitha, and Phoronida, which collectively constitute the protostome group Lophophorata. All lophophores are found in aquatic organisms.
The paraphyletic "Platyzoa" are a group of protostome unsegmented animals proposed by Thomas Cavalier-Smith in 1998. Cavalier-Smith included in Platyzoa the phylum Platyhelminthes, and a new phylum, the Acanthognatha, into which he gathered several previously described phyla of microscopic animals. Later it has been described as paraphyletic, containing the Rouphozoa and the Gnathifera.
Deuterostomes are bilaterian animals of the superphylum Deuterostomia, typically characterized by their anus forming before the mouth during embryonic development. The three major clades of extant deuterostomes include chordates, echinoderms and hemichordates.
Gnathifera is a clade of generally small spiralians characterized by complex jaws made of chitin. It comprises the phyla Gnathostomulida, Rotifera and Micrognathozoa. Chaetognatha has recently been recognised as closely related to the group, with it either being included within Gnathifera or the broader group Chaetognathifera. It may also include the Cycliophora.
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.
Nephrozoa is a major clade of bilaterians, divided into the protostomes and the deuterostomes, containing almost all animal phyla and over a million extant species. Its sister clade is the Xenacoelomorpha. The Ambulacraria are occasionally thought to be sister to the Xenacoelomorpha, forming the Xenambulacraria as basal Deuterostomia, or basal Bilateria invalidating Nephrozoa and Deuterostomia in multiple studies. The coelom, the digestive tract and excretory organs (nephridia), and nerve cords developed in the Nephrozoa. It has been argued that, because protonephridia are only found in protostomes, they cannot be considered a synapomorphy of this group. This would make Nephrozoa an improper name, leaving Eubilateria as this clade's name.
The Kryptotrochozoa are a proposed Lophotrochozoa clade. It consists of the Nemertea and Lophophorata. It is controversial.
Xenambulacraria is a proposed clade of animals with bilateral symmetry as an embryo, consisting of the Xenacoelomorpha and the Ambulacraria.
Parenchymia is a proposed clade encompassing Nemertea and Platyhelminthes. The clade was suggested in a 2019 study showing the clade as a sister to Annelida, with both groups together being sister to Lophophorata. The synapomorphies include similar organization of ciliary bands in the larva of both groups, as well as a lack of chitin, and is named for the abundant parenchyma found between the body wall and internal organs of both. A similar taxon, with Mollusca being likewise linked together with Symbion and Entoprocta, has been proposed in a clade called Tetraneuralia.
Centroneuralia is a proposed clade of animals with bilateral symmetry as an embryo, consisting of the Chordata and Protostomia, united by the presence of a central nervous system. An alternative to the traditional protostome-deuterostome dichotomy, it has found weak support in several studies. Under this hypothesis, Centroneuralia would be sister to Xenambulacraria at the base of Bilateria.
Tetraneuralia is a proposed clade of spiralian bilaterians uniting the phyla Mollusca and Entoprocta. First proposed in 2009 based on similarities between entoproct larvae and polyplacophoran molluscs, it was recovered in 2019 in a phylogenomic study by Marlétaz et al.
