Mitogenome Phylogenetics of Spiruromorpha Porpoise Parasite: Insights Into Phylogeny of Crassicauda magna

(1) Background: <i>Crassicauda magna</i> is a major parasite of large porpoises and whales and has been classified in the Habronematoidea family. However, there has been a great controversy regarding its classification. Mitochondria have an important function in revealing taxonomic and evolutionary history. (2) Methods: In this study, we sequenced the mitochondrial genome of <i>C. magna</i> and conducted a phylogenetic analysis with the mitochondrial sequences of species belonging to the Habronematoidea family. (3) Results: The complete mitochondrial genome was 13,604 bp and it has an AT-rich sequence and one non-coding region (NCR). The reconstruction of the ancestral state showed that the gene orders of all species in Spirurina were conserved. The phylogenetic tree indicates that <i>C. magna</i> is closer to <i>Heliconema longissimum</i> (Physalopteroidea) than <i>Tetrameres grusi</i> (Habronematoidea). (4) Conclusions: This study provides new evidence that <i>C. magna</i> is phylogenetically closer to Physalopteroidea at the molecular taxonomic level.