Comparative Analysis of Complete Mitochondrial Genomes of Four Tapeworms (Platyhelminthes: Cestoda) and Specific Primers for Identifying the Tapeworms from Chinese soft-shelled turtles (Pelodiscus sinensis)

Testudotaenia sp. WL-2016 (Platyhelminthes, Cestoda), as a member of Onchoproteocephalidea, was isolated from Pelodiscus sinensis in our previous study in 2016 (GenBank: KU761587.1). It was a new tapeworm found in China, and the only mitochondrial DNA of Testudotaenia reported worldwide. Traditional classification methods are challenging to identify specific cestode species rapidly for performing taxonomic research and disease control studies.We annotated the mitochondrial genome based on the previous sequencing, including analyses of nucleotide composition, codon usage. Ka/Ks, p‑distance, the nucleotide and amino acid similarity of the mitochondrial genomes of Dipylidium caninum, Digramma interrupta, Spirometra erinaceieuropaei, Testudotaenia sp. WL-2016 were analyzed and compared. Testudotaenia sp. WL-2016 and 65 others related cestodes were used to construct a phylogenetic tree with 10 common genes. We chose the trnG and COX3 genes to design specific PCR primers for identification. Testudotaenia sp. WL-2016 was strongly skewed away from A and biased towards G (AT skew= −0.292, GC skew= 0.22). Corresponding to the high T content (42.71%), codons also show relatively high T bias. Both Ka/Ks and p‑distance were less than 1. Data from the mitochondrial genome of Testudotaenia sp. WL-2016 is also valuable for species identification, phylogenies, and biogeography studies. The specific PCR primers enabled us to identify Testudotaenia sp. WL-2016 rapidly and accurately at the molecular level, thus providing a basis for classification and identification.