Turbellaria - Taxonomy

Time 2020-09-20 18:04:16

Web Name: Turbellaria - Taxonomy

WebSite: http://turbellaria.umaine.edu

ID:53647

Keywords:

Turbellaria,Taxonomy,

Description:

Cestoda: Gyrocotylidea / Amphilinidea + Eucestoda Trematoda: Aspidogastrea + DigeneaCite as "Tyler S, Schilling S, Hooge M, and Bush LF (comp.) (2006-2019) Turbellarian taxonomicdatabase. Version 1.8 http://turbellaria.umaine.edu"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-livingflatworms---those that don't parasitize other animals---while the other classesencompass the obligate parasites, most of which live in or on the bodies ofvertebrates. Turbellaria is, in particular, considered an invalid classbecause it is notmonophyletic. (It is either paraphyletic--that is, having descendants, namelythe parasitic classes, that are not classified within it [Ehlers, 1985]; or it could bepolyphyletic--that is, having arisen from more than one ancestor, one for theacoels and another for catenulidans andrhabditophorans [Bagu andRiutort, 2004; Phillip et al., 2011]). The term "turbellarian" can still be applied to those wormsthat were formerly classified in the Turbellaria, but the term "Turbellaria"(specifically, the capitalized taxon name) would have to be written inquotation marks to indicate its paraphyletic status. Not all turbellarians arefree-living. In recognition of recent proposals based on molecular sequences(particularly of 18s rDNA, some Hox genes, and, most recently, fuller genomicdata) the system displayed here treats the Acoelomorpha as separate from thephylum Platyhelminthes. The position and status of Acoelomorpha have beenvolatile in molecular systematics, some claiming that it itself isparaphyletic, many claiming that it (possibly as separate taxa Acoela andNemertodermatida) belongs near the base of the animal tree of life, as the mostbasal bilaterians---that is, the most primitive of any animal phylum outside ofthe sponges and cnidarians. The most recent genomic study (Phillip etal., 2011), placed the Acoelomorpha within the Deuterostomia, in a phylumXenacoelomorpha that includes also the enigmatic sack-like animalXenoturbella); Xenacoelomorpha is placed as sister group to theAmbulacraria (Ehinoderms + Hemichordata). Significantly, the earlierproposals that Acoelomorpha was the most primitive bilaterian---a controversial claim that did notmake sense in terms of the morphology of acoels---are now seen to be a resultof a statistical error known as long-branch attraction. The Platyhelminthes, as defined inthese molecular systems, would be only distantly related to the Acoelomorphaand classified as a lophotrochozoan phylum.This taxonomic database covers all turbellarian flatworms, includingparasitic turbellarians. The position of the major parasitic taxa (the otherclasses in the traditional system), encompassed now in the taxon Neodermata, isshown as proposed by cladistic systems based on morphological characters (seeBagu and Riutort, 2004, for summary of other proposed positions of theNeodermata).References citedBagu J, Riutort M (2004) Molecular phylogeny of the Platyhelminthes. Can J Zool 82:168-193.Ehlers U (1985) Das Phylogenetische System der Plathelminthes. Gustav Fischer, Stuttgart, New York. 317 ppPhilipp H, Brinkmann H, Copley RR, Moroz LL, Nakano H, Poustka AJ, Wallberg A, Peterson KJ, Telford MJ(2011)Acoelomorph flatworms are deuterostomes related to Xenoturbella.Nature 470(7333): 255-258 doi:10.1038/nature09676Data in this listing were initially compiled by Louise Bush using programsdeveloped by Seth Tyler. Dr. Bush's last update to the database was in 1991,the year of her death. Since 1991, the database has been updated by S. Tyler,Steve Schilling, and Matt Hooge, with help from specialists on various groupsof turbellarian platyhelminths, including Masaharu Kawakatsu, Ulrich Ehlers,Marco Curini-Galletti, Oleg Timoshkin.Availability of images is denoted with -symbols; these link to one or more images ofmostly systematic importance. Most of those of Rhabdocoela and Proseriata werekindly provided by Tom Artois and Ernest Schockaert of Universitair Centrum,Deipenbeek, Belgium; Matt Hooge, University of Maine; and Rick Hochberg,Smithsonian Institution, Fort Pierce, FL. Images of Acoela, Prolecithophora,and other Rhabdocoela were provided by Matt Hooge.The data pertaining to the Acoelomorpha is the most reliable, having beenchecked more thoroughly for accurracy in synonymy and literature citations.Notes in this section (reached with the "notes" links and the -symbols by the taxon names) are transcriptionsfrom or images of index cards that Louise Bush maintained. They summarizereferences to the taxa made in the literature (up to about 1991; more recentnotes are separated from Bush's with a horizontal line). Notes on groupsoutside the Acoelomorpha are mostly in the form of images of index cards. SteveSchilling transcribed Bush's notes and scanned the cards for this database. Heis also entering biogeographical data.Entry of data on the geographic distribution of species is supported in partby the Ocean Biogeographic Information System (OBIS). Steve Schilling is handling these data,gathering collection records of turbellarian species world-wide (both marineand freshwater). Species for which data have been entered are flagged with a"dist'n hyperlink, and clicking on this hyperlinkwill list those records. Maps of those collection sites can be reached usingthe map hyperlink and themap all distribution points at the end of eachlisting. (Resources we use for determining geographic coordinates ofcollecting sites and for drawing maps [Google Maps and Topozone] are listedseparately:mapping resources.) This is a work in progress. Copyrights for images remain with the originalprint publishers. Please send corrections toSeth Tyler, E-Mail styler at maine dot edu See also explanation ofPlatyhelminthes--the nature of a controversial phylum,which includes an explanation of Acoela and its relationship to the Platyhelminthes.Cite as "Tyler S, Schilling S, Hooge M, and Bush LF (comp.) (2006-2013) Turbellarian taxonomicdatabase. Version 1.7 http://turbellaria.umaine.edu"This material is based upon work supported by the National ScienceFoundation under Grant No. 0118804.

TAGS:Turbellaria Taxonomy 

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