Complete mitogenome of the edible sea urchin Loxechinus albus: genetic structure and comparative genomics within Echinozoa.

The edible Chilean red sea urchin, Loxechinus albus, is the only species of its genus and endemic to the Southeastern Pacific. In this study, we reconstructed the mitochondrial genome of L. albus by combining Sanger and pyrosequencing technologies. The mtDNA genome had a length of 15,737 bp and encoded the same 13 protein-coding genes, 22 transfer RNA genes, and two ribosomal RNA genes as other animal mtDNAs. The size of this mitogenome was similar to those of other Echinodermata species. Structural comparisons showed a highly conserved structure, composition, and gene order within Echinoidea and Holothuroidea, and nearly identical gene organization to that found in Asteroidea and Crinoidea, with the majority of differences explained by the inversions of some tRNA genes. Phylogenetic reconstruction supported the monophyly of Echinozoa and recovered the monophyletic relationship of Holothuroidea and Echinoidea. Within Holothuroidea, Bayesian and maximum likelihood analyses recovered a sister-group relationship between Dendrochirotacea and Aspidochirotida. Similarly within Echinoidea, these analyses revealed that L. albus was closely related to Paracentrotus lividus, both being part of a sister group to Strongylocentrotidae and Echinometridae. In addition, two major clades were found within Strongylocentrotidae. One of these clades comprised all of the representative species Strongylocentrotus and Hemicentrotus, whereas the other included species of Mesocentrotus and Pseudocentrotus.