Integrative taxonomy unveils a new species of Dugesia(Platyhelminthes,Tricladida,Dugesiidae)from the southern portion of the Taihang Mountains in northern China,with the description of its complete mitogenome and an exploratory analysis of mitochondrial gene order as a taxonomic character

A new species of Dugesia(Platyhelminthes,Tricladida,Dugesiidae)from northern China is described on the basis of an integrative approach,involving morphology,karyology,histology,molecular distance,molecular phylogeny,and mitochondrial gene order.Here,we present the complete mitogenome of the new species Du-gesia constrictiva Chen&Dong,sp.nov.This new species is mainly characterized by the presence of the following features:asymmetrical openings of the oviducts;large,cuboidal copulatory bursa;vasa deferentia opening through the ventro-lateral wall of the seminal vesicle;laterally compressed seminal vesicle;ventrally displaced ejaculatory duct,opening at the blunt tip of the penis papilla;long duct intercalated between semi-nal vesicle and diaphragm;chromosome complement diploid,with 16 metacentric chromosomes;mitochondrial gene order as follows:cox1-E-nad6-nad5-S2-D-R-cox3-I-Q-K-atp6-V-nad1-W-cox2-P-nad3-A-nad2-M-H-F-rrnS-L1-Y-G-S1-rrnL-L2-T-atp8-C-N-cob-nad4l-nad4.In triclads,mitochondrial gene order is considerably conserved between freshwater planarians and landflatworms,whereas it is variable between marine planarians and both fresh-water and landflatworms.The secondary structures of tRNAs are all equipped with 4 arms,excepting tRNA S1 and tRNA S2,which lack the D arm and have excessively enlarged loops.Numerous transpositions of tRNA are present between D.constrictiva and its congeners.Mitochondrial gene arrangements may form a new,additional tool for taxonomic studies.The phylogenetic tree based on analysis of the mitochondrial genome basically corroborates current classification of the higher taxa of planarianflatworms.