The linear mitochondrial genome of commensal hydroid Eutima japonica (Cnidaria, Hydrozoa, Eirenidae).

Here, we present the whole mitochondrial genome of commensal hydroid Eutima japonica McCrady 1859 (family Eirinidae); this is the first specimen of the family to have its mitogenome sequenced. The linear mitogenome is 15,315 bp in length and consists of 13 protein-coding genes (PCGs), large and small ribosomal subunits (rRNA), methionine and tryptophan transfer RNA (tRNA) genes (trnM and trnW), and a partial copy of cytochrome oxidase subunit I (cox1) pseudogene, as is typical for the class Hydrozoa. Nucleotide sequences of two cox1 genes at two ends of the linear mitogenome form a part of inverted terminal repeat. The overall genomic structure and gene arrangement of 13 PCGs were identical to the reported mitochondrial genomes of hydrozoans, except for the positions of two tRNA genes. Phylogenetic analysis of E. japonica 13 PCGs and other cnidarians recovers a closest relationship with the derived cluster of two hydrozoans, Laomedea flexuosa and Obelia longissimi within Leptothecata.