Lophotrochozoa

The lophotrochozoa (Lophotrochozoa sensu stricto) are a supergroup of animals made up of mollusks, lophophorates, worms such as annelids, among others. They are spirals, protostomes and initially included two important groups: Trochozoa, of animals with trochophore larvae such as molluscs; and Lophophorata, mostly sessile with lophophores (small tentacles). Subsequently, it has been expanded since it was concluded that flatworms and gastrotrics also belong to this clade. Recently, the mesozoans that include Orthonectida and Rhombozoa have been included, phyla that are very prone to the attraction of long branches and that, because of this, have prevented their relationships from being resolved in recent decades. The orthonectids turned out to be highly simplified annelids while the position of the rhombozoans is so far difficult to resolve.

This grouping arises after molecular studies and the cladistic methods currently used. All zoologists agree with these "new classifications" of the animal kingdom. The phylogenetic closeness to the gnatifers extended the group to what is now called Spiralia, a synonym of Lophotrochozoa sensu lato.

Phylogeny

The phylogeny of Lophotrochozoa is a difficult issue for specialists to resolve due to the large number of alternative hypotheses that are suggested in the various cladistic analyses. Both morphological and molecular data contradict each other and the position of the certain phyla is difficult to determine. Most molecular studies place the phyla very mixed. Lophotrochozoa phyla such as Rhombozoa, Platyhelminthes, Gastrotricha, Bryozoa, Entoprocta and Cycliophora are now known to have faster rates of evolution which prevent reconstructing a proper phylogenetic tree and lead to the long branch attraction factor.

Recent studies (2019) using slow-evolving species that are less prone to systematic error and cancatenated data have given the following result that is in many respects consistent with morphology:

An alternative phylogenetic tree published in the book "The Invertebrate Tree Of Life" (2020) is the one proposed by Gonzalo Giribet. The marked nodes are defended by the author: