Linearized representation of the mitochondrial gene arrangement for representatives of major chromadorean nematode clades, including two newly determined species ( B. xylophilus and P. vulnus ) in this study. Gene and genome size are not to scale. All genes are transcribed in the same direction (from left to right). The tRNAs are designated by single-letter abbreviation and two leucine and two serine tRNA genes are labeled, according to their anticodon sequence, as L1 (trnL-uag), L2 (trnL-uaa), S1 (trnS-ucu), and S2 (trnS-uga), respectively. The AT-rich non-coding region (NCR) is not indicated. The rectangular box indicates the most common gene arrangement pattern shared among the majority of Rhabditomorpha-Ascaridomorpha members.