The complete mitochondrial genome of the fire coral-inhabiting barnacleMegabalanus ajax(Sessilia: Balanidae): gene rearrangements and atypical gene content

Complete mitochondrial genome of the European common barnacle Perforatus perforatus Bruguière, 1789 (balanomorpha: balanidae)

This study is the first to sequence the complete mitochondrial genome (mitogenome) of Perforatus perforatus Bruguière, 1789 (Balanomorpha: Balanidae). The 15,536-bp long P. perforatus mitogenome contained a typical set of animal mitochondrial genes, along with one control region. The P. perforatus mitogenome had an inverted gene block (trnP-ND4L-ND4-trnH-ND5-trnF) between trnS(gct) and trnT. This inverted gene block had been detected six species in three subfamilies of the Balanidae family (Balaninae, Acastinae and Megabalaninae), but our results show that it is also present in Concavinae, in which P. perforatus is included. The phylogenetic tree based on the concatenated sequences of the 13 protein-coding genes and two rRNA genes showed that P. perforatus is closely associated with Acasta sulcate and Balanus trigonus within Balanidae.

Insights into the Deep Phylogeny and Novel Gene Rearrangement of Mytiloidea from Complete Mitochondrial Genome

The extant marine mussels which belong to the Mytiloidea are widespread species inhabiting mostly coastal waters, with some distributed in the deep sea. To clarify the classification systems and phylogenetic relationships range from genus to family level within Mytiloidea, new sequence was used in a phylogenetic analysis including all the available Mytiloidea mitochondrial genomes. In this study, the complete mitochondrial genome of Vignadula atrata is 15,624 bp in length and contains 12 protein-coding genes (PCGs, atp8 is absent), two ribosomal RNA genes, and 22 transfer RNA genes. Phylogenetic analysis based on 12 PCGs showed that it has a close relationship to Bathymodiolus. The analysis of gene rearrangements in the Pteriomorphia showed that the arrangements are highly variable across species, novel gene rearrangements were found within Mytiloidea. The V. atrata mitogenome was provided in detail, with notes on the sequence and a key to the species of Vignadula. This study provides a perspective on the taxonomic histories of the marine mussels and refines the unclear relationship between the origin and evolution of species in Mytiloidea within Bivalvia.

The Mitochondrial Genome of the Globally Invasive Barnacle Megabalanus coccopoma Darwin 1854 (Crustacea: Balanomorpha): Rearrangement and Phylogenetic Consideration within Balanomorpha

Megabalanus coccopoma (Darwin, 1854) is a globally invasive species in Balanomorpha (Crustacea). This species is a model organism for studying marine pollution and ecology. However, its mitogenome remains unknown. The mitogenome sequencing of M. coccopoma is completed in the present study. It has a 15,098 bp in length, including 13 protein-coding genes (PCGs), 2 ribosomal RNAs (rRNAs), 22 transfer RNAs (tRNAs), along with a putative regulatory area. A substantial A+T bias was observed in the genome composition (68.2%), along with a negative AT (0.82) and GC (−0.136) skew. Compared to the gene sequence of the ground model of pan-crustacea, 13 gene clusters (or genes), such as 10 tRNAs and 3 PCGs, were observed in a different order. This was in line with the previously observed large-scale gene rearrangements of Balanomorpha. Among the 37 genes, the gene cluster (M-nad2-W-cox1-L2-cox2-D-atp8-atp6-cox3-G- nad3-R-N-A-E-S1) Balanomorpha was conserved. Furthermore, phylogeny analysis indicated that the existing Balanomorpha species family was divided into nine rearrangement patterns, supporting the polyphyly of Balanoidea.

The first mitochondrial genome of Balanus trigonus Darwin, 1854 (Sessilia: Balanidae) and molecular phylogeny within Cirripedia

The triangle barnacle Balanus trigonus Darwin, 1854, a cosmopolitan inhabitant of tropical and warm temperate seas, is a member of robust system for the study of evolutionary processes in the intertidal zone. The first mitochondrial genome of B. trigonus is presented. The complete mitochondrial genome of B. trigonus is a circular molecule of 15,560 bp, which encodes 13 protein-coding genes (PCGs), 2 rRNA genes, and 22 tRNA genes. In comparison within Sessilia, the arrangement of the mitochondrial genome of B. trigonus is more similar to Megabalanus spp. than the congener Balanus balanus, which share a same inversion of a large gene block (P-nd4L-nd4-H-nd5-F). Phylogenetic analysis based on mitochondrial PCGs reveals that B. trigonus clusters with Acasta Sulcata (BP = 100), then grouped with Megabalanus volcano and Megabalanus ajax with high support (BP = 90). In further, more data and research are needed to reveal the phylogeny within Cirripedia.

Complete mitochondrial genome of Tetraclita squamosa squamosa (Sessilia: Tetraclitidae) from China and phylogeny within Cirripedia

Here we present the complete mitochondrial genome of Tetraclita squamosasquamosa, which is 15,191 bp in length with 67.20% AT content. It contains 13 protein-coding genes, 2 ribosomal-RNA genes and 22 transfer-RNA genes. All PCGs except nad4l in T. squamosasquamosa start with ATN, and terminated with a complete stop codon, except nad3. Phylogenetic analysis based on mitochondrial PCGs shows that T. squamosasquamosa is clustered with T. serrata into a branch (BP = 100). Our result is consistent with previous reports that genus Tetraclita and family Tetraclitidae are not monophyletic. This study contributes to further phylogenetic analysis within Cirripedia. 

The complete mitochondrial genome of Tetraclita japonica (Crustacea: Maxillopoda: Sessilia) from Zhejiang (China) and phylogeny within Sessilia

The complete mitochondrial genome of Tetraclita japonica (Crustacea: Maxillopoda: Sessilia) from Zhejiang (China) was presented (T. japonica ZJ). The genome is a circular molecule of 15,192 bp, all non-coding regions are 694 bp in length, and the longest one (307 bp) is located between 12S rRNA and trnK. Phylogenetic analysis based on mitochondrial PCGs shows that T. japonica ZJ clusters with T. japonica CN, and they grouped with T. japonica (BP = 100), then grouped with Tesseropora rosea, Tetraclita serrata, Tetraclita rufotincta, Epopella plicata, and Tetraclitella divisa successively . The phylogenetic tree indicated that the Balanidae and Archaeobalanidae are polyphyletic, while the Chthamalidae is monophyletic. The result can help us to understand the phylogenetic history within Sessilia.

The first mitochondrial genome of Capitulum mitella (Crustacea: Cirripedia) from China: revealed the phylogenetic relationship within Thoracica

Capitulum mitella (Crustacea: Cirripedia) is an important stalked barnacle. The first mitochondrial genome of C. mitella from China was presented, which is a circular molecule of 15,930 bp in length and AT content is 64.4%. It encodes 37 genes, including 13 PCGs, 22 tRNAs, and two rRNAs, which is consistent with most barnacles species reported. There are 15 genes encoded on the light strand and 22 genes encoded on the heavy strand. Identical to most barnacles species reported, srRNA and lrRNA genes are adjacent and separated only by trnV gene. Phylogenetic trees showed that C. mitella clustered with Pollicipes polymerus, indicating Pollicipedidae is monophyletic. However, Scalpelliformes was not monophyletic from the phylogenetic tree. From the level of order, the Lepadiformes was located at the base of the phylogenetic tree, indicating that its divergence time was earlier than Scalpelliformes. The results provided more insights into phylogenetic consideration at the genomic level within superorder Thoracica.

The first mitochondrial genome of Megabalanus tintinnabulum (Sessilia: Balanidae) from China: phylogeny within Cirripedia based on mitochondrial genes

Here we present the complete mitochondrial genome of Megabalanus tintinnabulum. The genome is 15,107 bp in length with a 67.35% AT content. It contains 13 protein-coding genes (PCGs), 2 rRNAs genes, and 22 tRNAs. Both rRNAs are encoded on the light strand, as in the other crustacean and barnacle mitochondrial genomes. Besides five tRNAs are encoded on the light strand (nad1, trnV, trnL1, trnC, trnQ, and trnK). Only one PCG is encoded on the light strand (nad1), whereas the other 12 PCGs are located on the heavy strand, which is consistent with M. ajax. Phylogenetic analysis based on mitochondrial PCGs shows that M. tintinnabulum is clustered with M. ajax into a branch (BP = 100), and the group with M. volcano with high support. This study contributes to further phylogenetic analysis within Cirripedia.

Mitochondrial genome of Tesseropora rosea: molecular evidence for non-monophyly of the genus Tetraclita

The complete mitochondrial genome of Tesseropora rosea (Tetraclitidae) was presented. The genome is a circular molecule of 15,330 bp, which encodes 13 PCGs, two rRNA genes, and 22 tRNA genes. The length of all non-coding regions is 768 bp, with the longest one speculated as the control region (255 bp), which is located between 12S rRNA and trnK. Phylogenetic analysis based on mitochondrial PCGs shows that T. rosea is nested within the genus Tetraclita, more closely related to Tetraclita japonica than to Tetraclita rufotincta or Tetraclita serrata. Thus, the monophyly of the genus Tetraclita is not supported.

Mitochondrial genome of the acorn barnacle Tetraclita rufotincta Pilsbry, 1916: highly conserved gene order in Tetraclitidae

The complete mitochondrial genome of the intertidal barnacle Tetraclita rufotincta Pilsbry, 1916 (Crustacea: Maxillopoda: Sessilia) is presented. The genome is a circular molecule of 15,236 bp, which encodes a set of 37 typical metazoan mitochondrial genes. All non-coding regions are 438 bp in length, with the longest one speculated as the control region (242 bp), which is located between srRNA and trnK. Comparison of the genome and those of three other species from Tetraclitidae shows that gene arrangement is identical, indicating that the mitochondrial gene order is highly conserved in the family. Moreover, in comparison with the pancrustacean ground pattern, the four species of Tetraclitidae share three large conserved gene blocks. Phylogenetic analysis based on 13 mitochondrial PCGs shows that Chelonbia testudinaria (Coronulidae) clusters with the four species of Tetraclitidae. Within Tetraclitidae, T. serrata clusters with T. japonica, and the two grouped with T. rufotincta with high support (BP = 100), with T. divisa as the most distantly related species (BP = 100).