The mitogenome sequence of a polychaete Hediste diadroma (Phyllodocida, Nereididae) was determined first in the genus Hediste. The circular genome is 15,765bp in size including 13 protein-coding genes (PCGs), 2 rRNA and 22 tRNA of which the order and structure is same as those of other Nereididae species. All PCGs use ATG as the start codon while for the stop codon, COI, ND5 and ND1 use an incomplete codon of T. The genome consists of 32.4% A, 18.2% C, 14.2% G, 35.2% T, showing a high content of A þ T similar to the other Phyllodocid polychaetes. Figure 1. Neighbour-joining tree for six species of the family Nereididae including Hediste diadroma and five other related species in Phyllodocida inferred from mitochondrial genomes. Terebellides stroemi (EU236701) derived from Terebellida was used as outgroup for tree rooting. Data set for Phylogenetic trees were used nucleotide sequences of 13 protein-coding genes. Numbers above the branches indicate NJ bootstrap values from 1000 replication. ARTICLE HISTORY KEYWORDS

The mitogenome sequence of sea slug, Chromodoris orientalis (Nudibranchia, Chromodorididae), has been decoded for the first time by coverage genome sequencing method. The overall base composition of C. orientalis mitogenome is 30.5% for A, 14.7% for C, 18.0% for G and 36.9% for T, and has low GC content 32.6%. The assembled mitogenome, consisting of 14,266 bp, has unique 13 protein-coding genes, 22 transfer RNAs, and two ribosomal RNAs genes. The C. orientalis mitogenome has the common mitogenome gene order and feature of Nudipleura (a clade of sea slugs and sea snails). The complete mitogenome of C. orientalis provides essential and important DNA molecular data for further phylogenetic and evolutionary analysis for sea slugs and sea snails.

The mitogenome sequence of Halichondria sp. was determined for the first time in this study. Specimens were identified as a new species belonging to genus Halichondria and more detailed taxonomic study is ongoing. Circular complete mitogenome is 19,687 bp in length, containing 14 proteincoding genes (PCGs), 2 ribosomal RNAs (rRNAs), and 25 transfer RNAs (tRNAs). Nucleotide composition of mitogenome consists of 28.9% A, 15.1% C, 21.9% G, 34.1% T, revealing high content of A þ T similar to the other Suberitid sponges. Results will be useful for inferring phylogenetic relationships among the members of Halichondriid.

Gymnogobius heptacanthus is a small intertidal species belonging to the family Gobiidae. Herein, we report the first sequencing and assembly of the complete mitochondrial genome of G. heptacanthus . The complete mitochondrial genome is 16,529 bp long and has the typical vertebrate mitochondrial gene arrangement, consisting of 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a control region. Phylogenetic analysis using mitochondrial genomes of 12 species showed that G. heptacanthus is clustered with G. urotaenia and G. petschiliensis and rooted with other Gobiidae species. This mitochondrial genome provides potentially important resources for addressing taxonomic issues and studying molecular evolution.

The mitogenome of rockfish, Sebastes oculatus, has been determined for the first time. Assembled mitogenome was 16,767 bp in length, including 13 protein-coding genes, 22 transfer RNA and two ribosomal RNA genes as well as the non-coding region. The order and structure are the same as those of other Sebastes species. S. oculatus was sister to S. nigrocinctus and this clade is closely related with S. rubrivinctus, as well as support for previously published complete mitochondrial genome trees (Sandel et al. 2018). The mitogenome of S. oculatus provides significant DNA molecular data for further identification and phylogenetic analysis within Scorpaenid.