Abstract:

The sample was obtained in the South China Sea, and its morphological characters are very similar to those of the Phyllidiidae species. It is elongated and ovoid, with a dark grey dorsal surface and irregular creamy-white verrucae, and two rows of orange protrusions in the center of the dorsal surface in parallel. In this study, this species was identified by mitochondrial whole genome sequencing and analyzed based on the sequences of protein-coding genes (PCGs). The results show that the full length of the mitochondrial genome is 14677 bp, containing 37 genes, which are 13 PCGs, 2 rRNAs and 22 tRNAs. The base composition of the mitochondrial genome is 30.4% A, 37.3% T, 15.0% C, and 17.3% G, with a preference for AT (67.7%). Among the 13 PCGs, there are 11 start codons conformed to the codon form of ATN, which used TTG as the start codon. The evolutionary tree was constructed using the maximum likelihood method, and the results show that this species is closely related to Phyllidiella pustulosa and clustered with Phyllidia ocellata. The complete mitochondrial genome sequence similarity between this species and P. pustulosa reached 94.6% by BLAST, and the gene sequence similarity of COX1 reaches 98.8%. Based on combined morphological characters and molecular identification, it is a new species of the genus Phyllidiella in the South China Sea, Phyllidiella nanhaiensis sp. nov.. The mitogenome of P. nanhaiensis sp. nov. will provide a reference for further study of the genus Phyllidiella, which is important for the study of species diversity and phylogeny of sea slugs.

Key words: Phyllidiella nanhaiensis sp. nov., mitochondrial genome, phylogenetic analysis, species identification