Mitochondrial genome of Micrura bella (Nemertea: Heteronemertea), the largest mitochondrial genome known to phylum Nemertea

Full Mitochondrial Genomes Reveal Species Differences between the Venerid Clams Ruditapes philippinarum and R. variegatus

In natural sea areas along the coast of China, venerid clams Ruditapes philippinarum and R. variegatus exhibit similar adult shell forms and are especially difficult to distinguish as spat and juveniles. This study used comparative mitochondrial genome analysis to reveal differences between these species. The results showed that: (1) the mitochondrial genomes of R. philippinarum and R. variegatus share a large number of similar gene clusters arranged in consistent order, yet they also display noncommon genes, with both gene rearrangements and random losses found; (2) the 13 protein-coding genes in R. philippinarum as well as two-fold and four-fold degenerate sites in R. variegatus have an evident AT bias; (3) the Ka/Ks ratio of the mitochondrial ATP8 gene was significantly higher in R. philippinarum than in R. variegatus, and an analysis of selection pressure revealed that the mitochondrial NADH dehydrogenase subunit 2 gene and NADH dehydrogenase subunit 6 gene of R. variegatus were under great selective pressure during its evolution; and finally, (4) the two species clustered into one branch on a phylogenetic tree, further affirming their phylogenetic closeness. Based on these results, we speculate that the species differences between R. variegatus and R. philippinarum are largely attributable to adaptive evolution to the environment. The present findings provide a reference for the development of germplasm identification.

Characterization of the complete mitochondrial genome of Quasilineus sinicus Gibson, 1990 (Nemertea: Heteronemertea) and its phylogenetic implications

In this study, we sequenced and characterized the complete mitochondrial genome (mitogenome) of Quasilineus sinicus Gibson, 1990 (Heteronemertea, Nemertea) using Illumina sequencing technology. The circular mitogenome was 16,358 bp in length and comprised 22 transfer RNA genes, 13 protein-coding genes, and two ribosomal RNA genes. Its overall base composition included 20.82% A, 41.06% T, 26.68% G, and 11.44% C; in fact, the mitogenome had a high A + T content of 61.88%. Furthermore, our phylogenetic analysis demonstrated that Paleonemertea, Pilidiophora, and Hoplonemertea were monophyletic groups, and Q. sinicus was most closely related to Iwatanemertes piperata.

Complete mitochondrial genome of the striped scat Selenotoca multifasciata (Perciformes: Scatophagidae)

The striped scat Selenotoca multifasciata is an ornamental and commercial fish in Asia. In the present study, we sequenced and annotated the complete mitochondrial genome of Selenotoca multifasciata. Its total length is 16,646 bp, and the mitochondrial genome is composed of 13 protein-coding genes, 2 rRNA genes, 22 tRNA genes and a non-coding control region. ND6 and eight tRNA genes were encoded on the light strand, whereas the remaining genes located on the heavy strand (H-strand). All the 16 mitochondrial genomes of the suborder Acanthuroidei available in GenBank were employed for phylogenetic analysis, and the result showed a close relationship between Selenotoca multifasciata and Scatophagus argus. This mitochondrial information may benefit relative ecological and phylogenetic studies.