Comparative mitogenomic analyses reveal cryptic diversity of the bryozoan Bugula neritina Linnaeus, 1758, in the Yellow Sea

The bryozoan Bugula neritina Linnaeus, 1758, is known to be a complex of three cryptic species, namely Types S, D and N. In the present study, we determined the mitochondrial genomic features of B. neritina sampled from Qingdao (QD), China, and compared them with those of the genome reported for a specimen sampled from Taean Gun (TG), South Korea. The B. neritina QD mitochondrial genome has a duplication of trnL2 and lacks trnV compared with B. neritina TG. Five tRNAs (trnL1, trnA, trnE, trnY and trnV) are encoded on the light-strand of B. neritina TG mitochondrial genome, but only one tRNA (trnA) is identified on the B. neritina QD mitochondrial light strand. In contrast to the B. neritina TG mitochondrial genome, deletion of trnV and duplication of trnL2 are identified in the B. neritina QD mtDNA, and three tRNAs (trnE, trnL1 and trnY) exhibit translocation and inversion. The genetic distance in 12 protein-coding genes (PCGs) (amino acids) between the two B. neritina was 0.079, which is higher than interspecific values of 10 lophotrochozoan genera selected for comparison. All these results from comparison between the two B. neritina clearly indicate that they are genetically distinct species. Phylogenetic analysis based on cox1 and lrRNA sequences suggested that B. neritina TG belongs to the widely distributed Type S and B. neritina QD represents a new cryptic type closely related to Type N. This new type is designated as Type Y, for its occurrence in the Yellow Sea. The geographical range of the different types of B. neritina awaits further studies.