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Abstract
Three new species of the cyclopoid copepod Halicyclops are described from river estuaries of Ariake Bay, Japan. Halicyclops continentalis sp. nov. is most similar to H. laminifer, but differs by the shape of an angular protuberance on the genital double‐somite and a serrate hyaline frill of the fourth urosomite. Halicyclops sinensis described by Tai and Chen is widely distributed in China and is identifiable to H. continentalis, indicating that the population in Ariake Bay is probably a continental relict. Halicyclops uncus sp. nov., belonging to the thermophilus group, is distinguishable by the shape of the lateral process on the genital double‐somite, a frill of the fourth urosomite and caudal rami; it is probably endemic to Japan. Halicyclops ariakensis sp. nov. differs from the other congeners by a combination of the shape of the prosome, urosomal hyaline frills and caudal ramus length; it is considered endemic to Ariake Bay.
Acknowledgements
We are indebted to F.D. Ferrari of the Smithsonian Institution, J.W. Reid of Virginia Museum of Natural History, S. Menu‐Marque of the University of Buenos Aires, I.M. Mirabdullayev of the Uzbek Academy of Sciences and K. Tomikawa of Hiroshima University for providing literature on Halicyclops, to M. Tanaka, T. Ohta, M. Hibino and T. Ishoda of Kyoto University, I. Kinoshita of Kochi University, and M. Azuma of Nagasaki University for their help in field collections, and to T.W. Miller of Ehime University for reviewing the text. Special thanks are due to J.W. Reid for her valuable comments and information. This study was supported in part by Grant‐in Aid for Scientific Research from JSPS (#18208019).