Complete mitochondrial genome of Turritella terebra bacillum

Complete mitochondrial genome of the worm snail Thylacodes adamsii (Littorinimorpha: Vermetidae) from South Korea

The worm snail Thylacodes adamsii (Mörch, 1859) (Littorinimorpha: Vermetidae) is a sessile gastropod that mainly inhabits rocky shores along the warm temperate to tropical ocean. Herein, the complete mitochondrial genome (mitogenome) of T. adamsii from South Korea was characterized. The genome is 14,913 bp in length and contains 13 protein-coding genes (PCGs), 22 tRNA genes, and 2 rRNA genes. The genome organization and base composition of T. adamsii are similar to those of other vermetids. A phylogenetic tree was reconstructed using maximum likelihood based on the nucleotide sequences of the 13 PCGs; this tree supported the monophyly of Vermetidae. The complete mitogenome of T. adamsii can assist with molecular species identification and vermetid phylogenetic research in the future.

The mitochondrial genome of Huaaristarchorum (Heude, 1889) (Gastropoda, Cerithioidea, Semisulcospiridae) and its phylogenetic implications

Research on complete mitochondrial genomes can help in understanding the molecular evolution and phylogenetic relationships of various species. In this study, the complete mitogenome of Huaaristarchorum was characterized to supplement the limited mitogenomic information on the genus Hua. Three distinct assembly methods, GetOrganelle, NovoPlasty and SPAdes, were used to ensure reliable assembly. The 15,691 bp mitogenome contains 37 genes and an AT-rich region. Notably, the cytochrome c oxidase subunit I (COX1) gene, commonly used for species identification, appears to be slow-evolving and less variable, which may suggest the inclusion of rapidly evolving genes (NADH dehydrogenase subunit 6 [ND6] or NADH dehydrogenase subunit 2 [ND2]) as markers in diagnostic, detection, and population genetic studies of Cerithioidea. Moreover, we identified the unreliability of annotations (e.g., the absence of annotations for NADH dehydrogenase subunit 4L [ND4L] in NC_037771) and potential misidentifications (NC_023364) in public databases, which indicate that data from public databases should be manually curated in future research. Phylogenetic analyses of Cerithioidea based on different datasets generated identical trees using maximum likelihood and Bayesian inference methods. The results confirm that Semisulcospiridae is closely related to Pleuroceridae. The sequences of Semisulcospiridae clustered into three clades, of which H.aristarchorum is one; H.aristarchorum is sister to the other two clades. The findings of this study will contribute to a better understanding of the characteristics of the H.aristarchorum mitogenome and the phylogenetic relationships of Semisulcospiridae. The inclusion of further mitochondrial genome sequences will improve knowledge of the phylogeny and origin of Cerithioidea.

The complete mitogenome of the invasive Japanese mud snail Batillaria attramentaria (Gastropoda: Batillariidae) from Elkhorn Slough, California, USA

Genomic analysis of the invasive marine snail Batillaria attramentaria from Elkhorn Slough, Moss Landing, California, USA using 150 bp paired-end Illumina sequences resulted in the assembly of its complete mitogenome. The mitogenome is 16,095 bp in length and contains 2 rRNA, 13 protein-coding, and 22 tRNA genes (GenBank Accession MN557850). Gene content and organization of B. attramentaria are identical to the Turritellidae and Pachychilidae. The phylogenetic analysis of B. attramentaria resolves it in a fully supported clade with these same two families in the superfamily Cerithioidea. Nucleotide BLAST searches of the Elkhorn Slough cox1 gene of B. attramentaria yielded identical sequences from invasive populations from California and British Columbia, and native populations from northeastern and central Japan. These data show that mitogenome sequencing is a useful tool for studying the classification and phylogenetic history Cerithioidea.

Comparative analysis of complete mitochondrial genomes with Cerithioidea and molecular phylogeny of the freshwater snail, Semisulcospira gottschei (Caenogastropoda, Cerithioidea)

In this study, we determined the complete mitochondrial genome (mt genome) of Semisulcospira gottschei for the first time and then compared it with the mt genome of species belonging to Cerithioidea. The mt genome consists of 13 protein-coding genes (PCGs), 2 ribosomal RNAs (rRNAs), 22 transfer RNAs (tRNAs) and non-coding region with a total length of 16,101 bp. The type of constitutive genes and the direction of the coding strand which appeared in the mt genome were the same as the ones observed in Cerithioidea except for the tRNA-Q and tRNA-R positions. The S. gottschei mt genome had a non-coding region with an AT-rich loop between tRNA-F and tRNA-C regions. In regard to molecular phylogeny, two types of analysis were performed to confirm the introgressive hybridization of S. gottschei and to identify the phylogenetic location among the species in Caenogastropoda. As a result, S. gottschei used in this study belonged to the same clade as other non-introgressed S. gottschei. As for the molecular phylogenic analysis of species belonging to Caenogastropoda, S. gottschei was found to be the closest to S. coreana taxonomically and to be included in Cerithioidea.