DOI: Four infraorders are recognized: i the Maricola marine planarians ; ii the Cavernicola a group of primarily cavernicolan planarians ; iii the Paludicola freshwater planarians ; and iv the Terricola land planarians.
The phylogenetic relationships among these infraorders have been analysed using morphological characters, but they remain uncertain. We use maximum parsimony and neighbour-joining methods and the characterization of a unique gene duplication tricladida plathelminthen involving the Terricola and the dugesiids to reconstruct the phylogeny.
The results show that the Maricola is monophyletic and is the primitive sister group to the rest of the Tricladida the Paludicola plus the Terricola. The Paludicola are paraphyletic since the Terricola and one paludicolan family, the Dugesiidae, share a more recent common ancestor than the dugesiids with other paludicolans dendrocoelids and planariids. A reassessment of morphological evidence may confirm the apparent redundancy of the existing infraorders Paludicola and Terricola.
In the meantime, we suggest replacing the Paludicola and Terricola with a new clade, the Continenticola, which comprises the families Dugesiidae, Planariidae, Dendrocoelidae and the Terricola.