The Mitochondrial Genome of Littoraria melanostoma Reveals Phylogenetic Relationship of Littorinimorpha

Littoraria melanostoma (Gray, 1839) is a most common species of gastropods in mangroves. They quickly respond during the early stage of mangrove restoration and usually form a dominant community within a certain period. We characterized the complete mitochondrial genome of the species. The whole mitogenome of L. melanostoma was 16,149 bp in length and its nucleotide composition showed high AT-content of 64.16%. It had 37 genes, including 13 protein-coding genes, two ribosomal RNA genes, and 22 transfer RNA genes, one control region between tRNA-Phe and COX3. The A/T compositions in the control region is 74.7%, respectively, and are much higher than the overall A/T composition of the mitochondrial genomes. The amino acid composition and codon usage of the mitochondrial genomes of from eight superfamilies of Littorinimorpha were analyzed, and the results showed that CUU (Leu), GCU (Ala), AUU (Ile), UCU (Ser), UUA (Leu), GUU (Gly) and UUU (Phe) are the commonly used codons in this order. The results of phylogenetic analysis were roughly consistent with morphological classification, which showed that L. melanostoma is closely related to L. sinensis, a rock-dwelling species that is widespread in the coastal intertidal zone of China. These results may provide a basis to understand the phylogeny and evolution of the Littorinimorpha.