The interrelationships of all major groups of Platyhelminthes: phylogenetic evidence from morphology and molecules

Abstract

We used a data matrix of 65 morphological characters from 25 ingroup and 6 outgroup taxa, and an alignmcnt comprising complete 18s rDNA scqucnccs from 82 species of parasitic and free-living Platylielminthcs and from 19 species of loivcr invcrtchratcs to analyse phylogenctic relationships ofvarious platyhclminth taxa.Of the 1358 unambiguously aligiiablc molecular positions, 995 wcrc variable and 757 \vcrc phylogcnetically informative (parsimony criterion); complete 18s rDNA sequences ranged in length from 1755 to 2873 lip.Main conclusions arc: Ncodermata are monophyletic, and the Trematoda, hlonogcnca and Cestoda within thcm arc monophylctic as well.The sister group of thc Ncodcrmata is all the otlicr Ncoophora; the Kalyptorhynchia, 'I'yphloplanida, Dalyclliida and Tcmiiocephalida form one clade, and the last three another.Rlonophyly of the Seriata is rejected, but Polycladida/ Rfacrostomida/Haplopharyngida arc monophylctic, as arc the last two taxa.As a consequence, validity of the taxon Trepaxonemata is rejected.Further studies must show the corrcct position of the Acoela and Ncmcrtodermatida.It is strcsscd that morphological and molecular data in some respects lead to contradictory results, for instance concerning the position of the Fccampiidac/ 1 ~r a .r t o n i n / Z ~i i t / ~~o ~h ~~~ and the rclativc position of the Lccithoepitlicliata.Denser sampling of taxa for molecular data, complcmcntary scqucnccs from independent gcncs, and inclusion of additional morphological data arc necessary to resolve thcsc contradictions.