Complete mitochondrial genome of Ophichthus brevicaudatus reveals novel gene order and phylogenetic relationships of Anguilliformes.

Generally, a teleostean group possesses only one type or a set of similar mitochondrial gene arrangement. However, two types of gene arrangement have been identified in the mitochondrial genomes (mitogenomes) of Anguilliformes. Here, a newly sequenced mitogenome of Ophichthus brevicaudatus (Anguilliformes; Ophichthidae) was presented. The total length of the O. brevicaudatus mitogenome was 17,773 bp, and it contained 13 protein-coding genes (PCGs), two ribosomal RNAs (rRNAs), 22 transfer RNA (tRNA) genes, and two identical control regions (CRs). The gene order differed from that of the typical vertebrate mitogenomes. The genes ND6 and the conjoint trnE were translocated to the location between trnT and trnP, and one of the duplicated CR was translocated to the upstream of the ND6. The duplication-random loss model was adopted to explain the gene rearrangement events in this mitogenome. The most comprehensive phylogenetic trees of Anguilliformes based on complete mitogenome was constructed. The non-monophyly of Congridae was well supported, whereas the non-monophyly of Derichthyidae and Chlopsidae was not supported. These results provide insight into gene arrangement features of anguilliform mitogenomes and lay the foundation for further phylogenetic studies on Anguilliformes.