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Adult form of a giant anguilliform leptocephalus Thalassenchelys coheni Castle and Raju 1975 is Congriscus megastomus (Günther 1877)


Anguilliform leptocephali of the genus Thalassenchelys Castle and Raju 1975 are remarkably large and peculiarly shaped eel larvae, whose adult form has been unknown since the discovery of the larvae in the 1950s. We found bigmouth conger Congriscus megastomus (Günther 1877) collected off the Pacific coasts of Japan to have mitochondrial DNA sequences (16S rDNA and COI) nearly identical to those of Thalassenchelys coheni Castle and Raju 1975 published to date and collected recently in the north Pacific. Vertebrae counts of C. megastomus were consistent with the myomere counts of T. coheni. We conclude that T. coheni, so-called larval species described by Castle and Raju (1975), is a junior synonym of C. megastomus. Therefore, the family to which the leptocephali belong must be Congridae.

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We are grateful to the captains and crew members of the RV Kaiyo-maru, the Fisheries Agency of Japan, and RV Soyo-maru, the Fisheries Research Agency, for their invaluable support during the research cruise. We are also grateful to K. Yamada, M. Oomura, and the crew of the bottom trawl fishing boat Hinode-maru for their help and cooperation during sampling in Suruga Bay, and A. Komatsu, Kochi Central Fisheries Guidance Office, for kindly providing bigmouth congers. We wish to express our sincere thanks to K. Hoshino, Seikai National Fisheries Research Institute, for photographing and aiding voucher specimens, and to S. Clarke and two anonymous referees for improving the manuscript. This work was funded by projects for research of marine fisheries stock assessment and evaluation for Japanese waters from the Fisheries Agency, Japan, the Fisheries Research Agency (FRA), and the Interdisciplinary Collaborative Research Program of the Atmosphere and Ocean Research Institute, the University of Tokyo.

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Corresponding author

Correspondence to Seinen Chow.

Additional information

H. Kurogi and S. Chow contributed equally to this work.

This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as 5CF59B1E-C215-4DFE-93BC-D130EE67F0CE.

This article was published as an Online First article on the online publication date shown on this page. The article should be cited by using the doi number.

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Kurogi, H., Chow, S., Yanagimoto, T. et al. Adult form of a giant anguilliform leptocephalus Thalassenchelys coheni Castle and Raju 1975 is Congriscus megastomus (Günther 1877). Ichthyol Res 63, 239–246 (2016).

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  • Anguilliformes
  • Giant leptocephalus
  • DNA barcoding
  • Thalassenchelys coheni
  • Congriscus megastomus