Complete mitochondrial genome of Acanthochitona defilippii (Polyplacophora: Chitonida) from South Korea

Abstract

The chiton (Polyplacophora) occupies a significant position in molluscan evolutionary history as one of the most primitive groups within the phylum Mollusca. Acanthochitona defilippii (Tapparone-Canefri 1874) (Chitonida: Acanthochitonidae) is a commonly found intertidal chiton species in South Korea. In this study, we characterized the complete mitochondrial genome of A. defilippii (14,999 bp long), comprising 13 protein-coding genes (PCGs), 22 transfer RNA genes, two ribosomal RNA genes, and an A + T rich region (166 bp). The base composition is as follows: 31.82% for A, 11.63% for C, 16.69% for G, and 39.86% for T. We reconstructed a maximum likelihood (ML) tree to elucidate phylogenetic relationships among the eight chitonid families using the nucleotide sequences of all PCGs. The ML tree revealed that A. defilippii clustered with Acanthochitona avicula (BP 100) within the family Acanthochitonidae. Acanthochitonidae formed a sister group with Mopaliidae. The results could provide a valuable understanding the phylogenetic relationships of chitonid species.

Keywords: Acanthochitona defilippii; Acanthochitonidae; chiton; mitochondrial genome; phylogeny.

Figure 1.

A Photograph of Acanthochitona defilippii attached on a rock surface. The photo was taken by the author (I Hyang Kim).

Figure 2.

Circular map of the complete mitochondrial genome of acanthochitona defilippii. The total length of the complete mitochondrial genome is 14,999 bp. Genes located on the outer side (ATP6, ATP8, COX1–3, ND2, and ND3) are on the heavy strand, while those on the inner side (CytB, ND1, ND4, ND4L, and ND6) are on the light strand. The inner circle illustrates the GC-skew, representing the variation from the overall average GC content across the entire sequence. The complete mitochondrial genome map was visualized using the Proksee program (Grant et al. 2023).

Figure 3.

A Maximum-likelihood tree reconstructed with nucleotide sequences of 13 mitochondrial PCGs from 23 chitonid species. The phylogenetic dataset consists of Chitonida (19 species), Callochitonida (1 species), and Lepidopleurida (3 species). The gray square box represents the examined species, A. defilippii in this strand. Scutopus ventrolineatus (caudofoveata) was set as an outgroup species. The number next to or below the species name indicated the accession number in GenBank. The numbers above each branch indicate the bootstrap support value. The following sequences were used: Acanthochitona avicula NC047426 (Irisarri et al. 2020), Acanthopleura echinate MN864062 (Irisarri et al. 2020), Acanthopleura loochooana OM047184 (unpublished), Acanthopleura vaillanti OQ355692 (Alnashiri et al. 2024), Callochiton steinenii MN864061 (Irisarri et al. 2020), Chiton albolineatus NC047425 (Irisarri et al. 2020), Cryptochiton stelleri NC026850 (Irisarri et al. 2014), Cyanoplax caverna NC026848 (Irisarri et al. 2014), Dendrochiton gothicus NC047424 (Irisarri et al. 2020), Hanleyella oldroydi NC047423 (Irisarri et al. 2020), Katharina tunicata NC001636 (Boore and Brown 1994), Lepidozona coreanica NC046935 (Sun et al. 2023), Leptochiton nexus NC047422 (Irisarri et al. 2020), Mopalia retifera NC068065 (unpublished), Nierstraszella lineata NC047421 (Irisarri et al. 2020), Nuttallina californica NC026849 (Irisarri et al. 2014), Nuttallochiton mirandus MN864053 (Irisarri et al. 2020), Plaxiphora albida MN864050 (Irisarri et al. 2020), Scutopus ventrolineatus NC025284 (Osca et al. 2014), Sypharochiton pelliserpentis NC024174 (Veale et al. 2016), Sypharochiton sinclairi NC024173 (Veale et al. 2016), Tonicia forbesii MN864054 (Irisarri et al. 2020) and Tonicina zschaui MN864051 (Irisarri et al. 2020).