A ROBUST MOLECULAR PHYLOGENY OF THE TRICLADIDA (PLATYHELMINTHES, SERIATA) WITH A DISCUSSION ON MORPHOLOGICAL SYNAPOMORPHIES

The suborder Tricladida (Platyhelminthes: Turbellaria, Seriata) compri ses most well-known species of free-living flatworms. Four infraorders are recognized: (i) the Maricola (marine planarians); (ii) the Cavern icola (a group of primarily cavernicolan planarians); (iii) the Paludi cola (freshwater planarians); and (iv) the Terricola (land planarians) . The phylogenetic relationships among these infraorders have been ana lysed using morphological characters, but they remain uncertain. Here we analyse the phylogeny and classification of the Tricladida, with ad ditional, independent, molecular data from complete sequences of 18S r DNA and 18S rRNA. We use maximum parsimony and neighbour-joining metho ds and the characterization of a unique gene duplication event involvi ng the Terricola and the dugesiids to reconstruct the phylogeny. The r esults show that the Maricola is monophyletic and is the primitive sis ter group to the rest of the Tricladida (the Paludicola plus the Terri cola). The Paludicola are paraphyletic since the Terricola and one pal udicolan family, the Dugesiidae, share a more recent common ancestor t han the dugesiids with other paludicolans (dendrocoelids and planariid s). A reassessment of morphological evidence may confirm the apparent redundancy of the existing infraorders Paludicola and Terricola. In th e meantime, we suggest replacing the Paludicola and Terricola with a n ew clade, the Continenticola, which comprises the families Dugesiidae, Planariidae, Dendrocoelidae and the Terricola.