Complete mitochondrial genome of blunt slipper lobsters Scyllarides squammosus (H. Milne Edwards, 1837)

Abstract The complete mitochondrial genome of Scyllarides squammosus was first determined and characterized. With a length of 15,644 bp, it consists of 22 tRNA genes, 2 rRNA genes, 13 protein-coding genes (PCGs), and 1 control region. The nucleotide composition is significantly biased with AT contents of 65.6%. Among these PCGs, five of them used an unusual initiation codon, and nine genes ended with an incomplete or abnormal stop codon. Two microsatellites were identified and located in COX3 gene and D-loop region. Phylogenetic analysis demonstrated that S. squammosus was first clustered with Scyllarides latus, which was consistent with the previous work.

Scyllarides squammosus; mitochondrial genome; phylogenetic analysis Scyllarides squammosus, known as scaly slipper lobster or blunt slipper lobster, is a highly valuable species in the family Scyllaridae, Achelata, the price of which is almost similar to lobster due to scarce and delicacy. S. squammosus habits on reefs and rocky areas commonly at depth of 7.5-71 m. It has an extensive distribution in the Indo-West Pacific region: from East Africa to Japan, Hawaii, Melanesia, New Caledonia, and Australia. Till now, many researchers have long studied the biology of S. squammosus such as feeding behavior (Lau 1987), fecundity and egg size (DeMartini and Williams 2001), sexual maturity (DeMartini et al. 2005), gamete and larval development (Matthews 1954;Coutures 2001), fishery (Clarke and Yoshimoto 1990 The samples were collected from Huanqiu wharf of Wenchang, Hainan province, China (19 33 0 57.91 00 N, 110 49 0 12.10 00 E), and stored in Qionghai research base of Hainan Academy of Ocean and Fisheries Sciences for reference and DNA extraction.
The complete mitogenome sequence of S. squammosus is 15,644 bp in length (GenBank Accession no. MK783265). The base content was 31.2% A, 13.2% G, 34.3% T, and 21.2% C. The 65.6% of (A þ T) showed great preference to AT. the circular mitogenome contained 22 tRNA genes, 2 rRNA genes, 13 protein-coding genes (PCGs), and 1 control region (Dloop). Four PCGs (ND1, ND4, ND4L, and ND5), eight tRNA genes and two rRNA genes were encoded on the light strand, the others were encoded by the heavy strand.
The 22 tRNA genes of the S. squammosus mitogenome ranged in length from 63 to 73 bp. The genes tRNA-Leu and tRNA-Ser have two copies each, identified with different codons (tRNA-leu uses TAA and TAG; tRNA-Ser uses TCT and TGA). The 12S rRNA is located between tRNA-Val and D-loop with the length of 863 bp, and the 16S rRNA is 1339 bp, located between tRNA-Val and tRNA-Leu. Except for five PCGs using an abnormal start codon (ND1 and ND4L use TTA; COX1 uses ACG; ND4 uses CAG; ND5 uses AAC), the others use a common initiation codon ATN. We also found that except for 4 PCGs using TAA or TAG, the stop codon of the other nine genes were abnormal: COX2, ND2, ND3, and ND5 use a single base T; ND4 uses AT; COX1 uses TT; CYTB uses TG; ND4L uses CAT; and ND1 uses CAC. With a length of 716 bp, the control region is located between 12S rRNA and tRNA-Ile. Two microsatellites (SSR) were found in the mitogenome of S. squammosus using MISA software. The two (T) 10 SSRs were located in the codon region of COX3 gene and the non-codon region of D-loop, respectively.
To investigate the phylogenetic relationship of S. squammosus in the Achelata, a phylogenetic tree was constructed based on the13 PCGs nucleotide sequences of 16 Achelata species mitogenome available in the GenBank using the maximum-likelihood (ML) method with 1000 bootstrap replicates. The result (Figure 1) show that S. squammosus was first clus-tered with Scyllarides latus, which was consistent with the previous work (Palero et al. 2016).

Disclosure statement
No potential conflict of interest was reported by the authors.