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BioMed Research International
Volume 2013 (2013), Article ID 147064, 11 pages
Research Article

Evolutionary Relations of Hexanchiformes Deep-Sea Sharks Elucidated by Whole Mitochondrial Genome Sequences

1Department of Molecular Life Science, Division of Basic Medical Science and Molecular Medicine, Tokai University School of Medicine, 143 Shimokasuya, Isehara, Kanagawa 259-1143, Japan
2Fisheries Science Center, The Hokkaido University Museum, 3-1-1 Minato-cho, Hakodate, Hokkaido 041-8611, Japan
3Division of Human Genetics, Department of Integrated Genetics, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka 411-8540, Japan
4Division of Science Interpreter Training, Komaba Organization for Education Excellence College of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
5Shimonoseki Marine Science Museum, 6-1 Arcaport, Shimonoseki, Yamaguchi 750-0036, Japan
6Department of Clinical Pharmacology, Division of Basic Clinical Science and Public Health, Tokai University School of Medicine, 143 Shimokasuya, Isehara, Kanagawa 259-1143, Japan
7Centre for Forensic Science, The University of Western Australia, Nedlands, WA 6008, Australia
8Department of Marine Biology, School of Marine Science and Technology, Tokai University, 3-20-1 Orido, Shimizu, Shizuoka 424-8610, Japan

Received 1 March 2013; Accepted 26 July 2013

Academic Editor: Dietmar Quandt

Copyright © 2013 Keiko Tanaka et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Hexanchiformes is regarded as a monophyletic taxon, but the morphological and genetic relationships between the five extant species within the order are still uncertain. In this study, we determined the whole mitochondrial DNA (mtDNA) sequences of seven sharks including representatives of the five Hexanchiformes, one squaliform, and one carcharhiniform and inferred the phylogenetic relationships among those species and 12 other Chondrichthyes (cartilaginous fishes) species for which the complete mitogenome is available. The monophyly of Hexanchiformes and its close relation with all other Squaliformes sharks were strongly supported by likelihood and Bayesian phylogenetic analysis of 13,749 aligned nucleotides of 13 protein coding genes and two rRNA genes that were derived from the whole mDNA sequences of the 19 species. The phylogeny suggested that Hexanchiformes is in the superorder Squalomorphi, Chlamydoselachus anguineus (frilled shark) is the sister species to all other Hexanchiformes, and the relations within Hexanchiformes are well resolved as Chlamydoselachus, (Notorynchus, (Heptranchias, (Hexanchus griseus, H. nakamurai))). Based on our phylogeny, we discussed evolutionary scenarios of the jaw suspension mechanism and gill slit numbers that are significant features in the sharks.