The Study On Microstructure Of Spines From Four Sea Urchins And Phylogenetic Based On Complete Mitochondrial Genome

This study used the traditional method and electron microscopy (SEM) to the morphological study of Salmacis virgulata & Salmacis bicolor focused on the spine and pedicellaria. Also the analysis of mtDNA genome of two Salmacis were conducted by using long-PCR and conventional polymerase chain reaction (PCR), using the mitochondrial genome sequence of the two kinds of sea urchins, carring on the analysis comparison, and combining with other 9 kinds of arch of tooth mesh sea urchins* all mitochondrial genome sequence for the phylogenetic relationship and genetic differentiation research. This research can provide basic data and molecular result for the sea urchin taxonomy and mitochondrial genome.S. virgulata and S. bicolor have significant difference in primary spine and secondary spine, but are similar in clavula. Pedicellarias differentiation of four kinds of sea urchin is obvious, especially tridactylous pedicellaria and globiferous pedicellaria. Ophicephalous pedicellaria, tridactylous pedicellaria, globiferous pedicellaria and triphyllous pedicellaria have a lot differentiation in external form, number and location of lateral teeth, form and distribution of sawtooth. This study described these differences systematically and provided reliable basis for classification of Salmacis and Temnopleurus.The mitogenome lengths of S. virgulata and S. bicolor are 15762bp and 15767bp. All the two mitogenomes carried set of 22 tRNAs.2 rRNAs,13 protein-coding genes as well as a non-coding control region as in other urchins. And the ribosomal RNA had higher conservative. The skew value of two urchins was slightly different. The nucleotide composition of two urchins showed distinct AT bias, in addition to the control area AT content difference is small and generally between 60% to 65%. the 16s rRNA showed an AT enrichment region, and AT levels of 16s rRNA was obviously higher than 12s rRNA.Two sea urchin protein-coding genes base content AT content in the H chain was lower than the L chain, the AT content increased gradually from the first to third codon positions. The 13 mitochondrial protein-coding genes contained 3819 codons (excpt termination codon), mostly with ATG or ATA or GTG or ATC as their start codon. All the 13 mitochondrial protein-coding genes used TAG or TAA as their complete stop codon. The length range of 22 tRNA was from 68bp to 74bp, and there also existed obvious AT bias, but was similar in H chain and L chain. All tRNA genes could putatively form typical cloverleaf secondary structures with the exception of tRNASer (AGN).Based on the protein-coding genes (excluding ND6 gene and non-coding regions), 2 rRNAs genes and 22 tRNAs genes of 13 species of Camarodonta, this study used the maximum quasi likelihood (ML) and Bayesianphylogenetic respectively to construct phylogenetic tree, calculate genetic distance with Kimura-2-parameter. And the results of Bayes tree based on complete mitogenome sequences completely consistent with the ML phylogenetic trees constructed based on concatenated protein-coding genes, the ML phylogenetic trees constructed based on concatenated rRNA genes showing slightly different, and the significant difference was found in the ML phylogenetic trees constructed based on concatenated tRNA genes. Two Sahnacis in this experiment showed a recent genetic relationship of each other consistent with morphological classification results, and the genetic distance between 4 Salmacis and other 11 kinds of sea urchin was relatively far away.