| Molluscs, Annelid, Brachiopod, Bryozoa, Ribbon worms|
The Lophotrochozoa (/ləˌfɒtroʊkoʊˈzoʊə/, "crest/wheel animals") are a major grouping of protostome animals. The taxon was discovered based on molecular data. Molecular evidence such as a result of studies of the evolution of small-subunit ribosomal RNA (rRNA) supports the monophyly of the phyla listed in the infobox shown at right.
The word "lophotrochozoan" is sometimes equated with spiralian. When used in a broader sense (sensu lato), it can include rotifers and platyhelminthes. When used sensu stricto, it refers to a subgroup of Spiralia.
The Lophotrochozoa comprise two groups, the trochozoans and the lophophorata. The exact relationships between the different phyla are not entirely certain.Trochozoans produce trochophore larvae, which have two bands of cilia around their middle. Previously these were treated together as the Trochozoa, together with the arthropods, which do not produce trochophore larvae but were considered close relatives of the annelids because they are both segmented. However, they show a number of important differences, and the arthropods are now placed separately among the Ecdysozoa. The Trochozoa include the Nemertea, Mollusca, Sipuncula, and Annelida.
The Lophophorata are united by the presence of a lophophore, a fan of ciliated tentacles surrounding the mouth, and so were treated together as the lophophorates. They are unusual in showing radial cleavage, and some authors considered them deuterostomes. The ‘clade’ Lophotrochozoa was founded on evidence from 18S ribosomal RNA, but a later study on LSU and SSU ribosomal genes suggested that the Lophophorata is polyphyletic.
Other phyla are included on the basis of molecular data.
With the introduction of Platytrochozoa and Rouphozoa, the cladogram is as follows: