Turbellaria - Taxonomy

Turbellarian Taxonomic Database

A listing of the taxonomy of turbellarians
(formerly class Turbellaria of the phylum Platyhelminthes)

Cite as "Tyler S, Schilling S, Hooge M, and Bush LF (comp.) (2006-2025) Turbellarian taxonomic database. Version 2.2 https://turbellaria.umaine.edu"

About turbellarians

Traditional, pre-cladistic systems placed the flatworms in a single phylum, the Platyhelminthes, subdivided into the classes Turbellaria, Monogenea, Trematoda, and Cestoda. Turbellarians are the largely free-living flatworms---those that don't parasitize other animals---while the other classes encompass the obligate parasites, most of which live in or on the bodies of vertebrates. Turbellaria is, in particular, considered an invalid class because it is not monophyletic. (It is either paraphyletic--that is, having descendants, namely the parasitic classes, that are not classified within it [Ehlers, 1985]; or it could be polyphyletic--that is, having arisen from more than one ancestor, one for the acoels and another for catenulidans and rhabditophorans [Baguñà and Riutort, 2004; Phillipé et al., 2011]). The term "turbellarian" can still be applied to those worms that were formerly classified in the Turbellaria, but the term "Turbellaria" (specifically, the capitalized taxon name) would have to be written in quotation marks to indicate its paraphyletic status. Not all turbellarians are free-living.

In recognition of recent proposals based on molecular sequences (particularly of 18s rDNA, some Hox genes, and, most recently, fuller genomic data) the system displayed here treats the Acoela and Nemertodermata as separate from the phylum Platyhelminthes. The position and status of Acoela and Nemertodermatida have been volatile in morphology-based as well as molecular-systematics studies. They have been placed together in the group Acoelomorpha in more recent morphological studies, some molecular-sequence-based studies place either or both at the base of the animal tree of life, as the most basal bilaterians---that is, the most primitive of any animal phylum outside of the sponges and cnidarians. Phylogenomic studies place the Acoela either within the Deuterostomia (Philippé et al., 2011) or more basally as a sister group to all other bilaterians (Hejnol et al., 2009; Cannon et al., 2016). As a deuterostome, the Acoela would be in a phylum Xenacoela (Redmond, 2024) that includes also the enigmatic sack-like animal Xenoturbella. The Xenacoela would be sister group to the Nemertodermatida, in the taxon Xenacoelomorpha, which is itself placed as sister group to the Ambulacraria (Echinodermata + Hemichordata). Significantly, proposals that either Acoela or Nemertodermatida are most basal of all bilaterians Seth Tyler, E-Mail "styler at maine dot edu"

database last modified: 19 November, 2024

Cite as "Tyler S, Schilling S, Hooge M, and Bush LF (comp.) (2006-2025) Turbellarian taxonomic database. Version 2.2 https://turbellaria.umaine.edu"

This material is based upon work supported by the National Science Foundation under Grant No. 0118804.