The first mitochondrial genome of Fistulobalanus albicostatus (Crustacea: Maxillopoda: Sessilia) and phylogenetic consideration within the superfamily Balanoidea

Abstract The first complete mitochondrial genome of the intertidal barnacle Fistulobalanus albicostatus Pilsbry, 1916 (Crustacea: Maxillopoda: Sessilia) is presented. The genome is a circular molecule of 15,665 bp, which encodes a set of 37 typical metazoan genes. All non-coding regions are 438 bp in length, with the longest one speculated as the control region (264 bp), which is located between srRNA and trnI. All protein-coding genes (PCGs) have an ATD (ATA, ATT, or ATG) start codon, except nad1, which is initiated with GTG. Remarkably, cox3, cob, nad1-5 have incomplete stop codons (T–– or TA–) and the remaining PCGs have the complete stop codon (TAA). Phylogenetic analysis based on 13 mitochondrial PCGs shows that the members of the Archaeobalanidae and Balanidae intermingle with species from Pyrgomatidae. The results supposed that Balanidae and Archaeobalanidae are non-monophyly.

(Crustacea: Maxillopoda: Sessilia) is a common acorn barnacle in mangroves and on soft shores, inhabiting on rocks, mollusk shells, tree trunks, and mangrove leaves (Prabowo and Yamaguchi 2005;Chang et al. 2017;Hayashi 2017). The species is widely distributed in East Asia, including Japan, Korea, and China (Newman and Ross 1976;Chan and Leung 2007;Ping-Hung et al. 2007). The work presents the first complete mitochondrial genome of F. albicostatus. Specimen of F. albicostatus was collected from Qidong (32 1 0 24 00 N, 121 44 0 21 00 E), Jiangsu Province, China. Genomic DNA was isolated using TIANamp Marine Animal DNA Kit (TIANGEN, Beijing, China) following the manufacturer's protocol, which was stored at Marine Museum of Jiangsu Ocean University (accession number: Fal-002). The amplification of internal fragments and long fragments followed the procedures described in our previous study (Chen et al. 2019). PCR products were purified (GeneMark), cloned (pGEMT easy, Promega, Madison, WI) and sequenced (MAP BIOTECH, Shanghai, China).
The complete mitochondrial genome of F. albicostatus is a circular molecule of 15,665 bp in length, encodes 13 proteincoding genes (PCGs), 2 ribosomal RNAs (rRNAs), 22 transfer RNAs (tRNAs), and 1 non-coding region (GenBank accession number: MK617531). Four PCGs and two rRNAs are encoded on the light strand (nad1, nad4, nad4L, and nad5), while the other nine PCGs are located on the heavy strand.
The base composition was 36.0% A, 17.4% C, 12.1% G, and 34.5% T. The overall A þ T content of the mitochondrial genome of F. albicostatus is 70.6%. Non-coding regions make up 438 bp, with the longest one speculated as the control region (264 bp), which is located between srRNA and trnI. The srRNA (AT content: 72.4%) and lrRNA (AT content: 74.6%) are 898 bp and 1302 bp, respectively. All PCGs have an ATD (ATA, ATT, or ATG) start codon, except nad1, which is initiated with GTG. Remarkably, cox3, cob, and nad1-5 have incomplete stop codons (T-or TA-) and the remaining PCGs have the complete stop codon (TAA).
To investigate the phylogenetic position and the inner relationships of the suborder Balanomorph, phylogenetic trees were constructed with nucleotide sequences of 13 PCGs from 22 complete mitochondrial genomes of Sessilia, and Lepas australis (NC_025295) as outgroup species, using maximum likelihood with MEGA7 (Kumar et al. 2016) (Figure 1). In the tree, F. albicostatus is the most primitive member within the superfamily Balanoidea. Within the superfamily Balanoidea, the tree is divided into two parts. One part has two species of Megabalanus (M. ajax and M. volcano) cluster with Acasta sulcata, which belongs to Archaeobalanidae. Two are grouped with Balauns balanus, with being the most distantly related taxon. In another part, Nobia grandis and Savignium sp. BKKC-2013 are grouped together with high support (BP ¼ 100), and then cluster with Armatobalanus allium and Striatobalanus amaryllis. The members of the Archaeobalanidae and Balanidae intermingle with species from Pyrgomatidae. The results supposed that Balanidae and Archaeobalanidae are non-monophyly, which is consistent with previous researches (Tsang et al. 2014Shen et al. 2015).

Disclosure statement
No potential conflict of interest was reported by the author(s).

Data availability statement
The data that support the findings of this study are openly available in GenBank of NCBI at https://www.ncbi.nlm.nih.gov, reference number MK617531.