The complete mitochondrial genome of Cypraea tigris from the South China Sea has been determined, which was the first report of complete mitogenome in the superfamily Cypraeoidea. It is 16,177 bp long and consists of 21 tRNA genes, 2 rRNA genes, 13 protein-coding genes (PCGs), and 1 control region. The base composition of C. tigris mitogenome is biased (A, G, T, and C were 28.8, 17.9, 37.1, and 16.3%, respectively) with A þ T contents of 58.5%. All of the PCGs use a typical start codon (ATN) and a complete stop codon (TAA or TAG) as normal. The maximum-likelihood tree demonstrated that the Cypraeoidea was closer to the superfamily Tonnoidea, and further clarified the phylogenetic relationships of each superfamily in Littorinimorpha.

The complete mitochondrial genome of Anadara antiquata was first determined. With a length of 45,454 bp, it consists of 29 tRNA, 2 rRNA, and 17 protein-coding genes (PCGs). The non-coding region was large and atypical around the genome with total 24,162 bp long. The nucleotide composition is significantly biased with AT contents of 62.2%. PCGs have five types of start codon, and terminate with a complete stop codon TAA or TAG. 19 microsatellites (SSRs) were identified in mitogenome sequences. Phylogenetic analysis demonstrated that A. antiquata was first clustered with Anadara vellicate, then together with Tegillarca granosa.

In this study, we first determined and characterized the complete mitochondrial genome of longlegged spiny lobster Panulirus longipes from South China Sea. The P. longipes mitogenome is 15,739 bp long, and consists of 22 tRNA genes, two rRNA genes, 13 protein-coding genes (PCGs), and one control region. The nucleotide composition of P. longipes mitogenome is significantly biased (A, G, T, and C was 32.06%, 14.36%, 32.42%, and 21.16%, respectively) with A þ T contents of 64.48%. Among 13 PCGs, COX1 gene used an unusual initiation codon CAA, COX1, COX2, ND4 and CYTB genes were ended with an incomplete stop codon T, and ND5 gene with an abnormal stop codon ATT. One microsatellite (C) 10 was identified in P. longipes mitogenome located in the control region. Phylogenetic tree showed that P. longipes was first clustered with Panulirus cygnus, then together with P. japonicus and P. argus.

The complete mitochondrial genome of Trachycardium flavum from South China Sea was first determined in this study, which is 16,596 bp in length. The base composition of the mitogenome is a less biased (A, G, T, and C was 21.5%, 26.3%, 37.0%, and 15.2%, respectively) with A þ T contents of 58%. It consists of 24 tRNA genes, two rRNA genes, and 12 protein-coding genes (PCGs). No typical control region was found in non-coding sequence. Interestingly, ATP8 genes was absence same as most shellfish. Nine PCGs use a special start codon TTG, and the other three genes use a normal initiation codon ATN. Except ND6 use a single base G as the stop codon, the others all end with the normal stop codon TAG. The phylogenetic tree showed that T. flavum was first clustered with Fulvia mutica, Cerastoderma edule, and Acanthocardia tuberculate, which all belong to Cardiidae.