ZOOTAXA ISSN 1175-5326 (print edition) ISSN 1175-5334 (online edition) Accepted by M. Marinov: 28 Feb. 2020; published: 13 May 2020 171 Zootaxa 4778 (1): 171–195 https://www.mapress.com/j/zt/ Copyright © 2020 Magnolia Press Article https://doi.org/10.11646/zootaxa.4778.1.7 http://zoobank.org/urn:lsid:zoobank.org:pub:F938B2DE-5F81-4B1F-90CB-8A46B9DC4E20 The genus Gynacantha Rambur, 1842 in the South Pacific (Odonata: Anisoptera: Aeshnidae) GUNTHER THEISCHINGER 1 , MILEN MARINOV 2 , SETH BYBEE 3 , COLIN JENSEN 3 , JÖRN THEUERKAUF 4 & BINDIYA RASHNI 5 1 Australian Museum, Entomology, 6 College Street, Sydney, NSW 2010. � theischingergunther@gmail.com https://orcid.org/0000-0002-5207-2626 2 Biosecurity Surveillance & Incursion Investigation Plant Health Team, Ministry for Primary Industries, 14 Sir William Pickering Drive, Christchurch 8544, New Zealand. � milen.marinov@mpi.govt.nz https://orcid.org/0000-0003-3284-2555. 3 Biology Department & Monte L. Bean Museum Brigham Young University, Provo, UT 84606, USA � seth.bybee@byu.edu https://orcid.org/0000-0001-6224-6303; � colinjensen333@gmail.com https://orcid.org/0000-0002-6856-1790 4 Museum and Institute of Zoology, Polish Academy of Sciences, Wilcza 64, 00-679 Warsaw, Poland. � jtheuer@miiz.eu https://orcid.org/0000-0002-7273-3073 5 NatureFiji-MareqetiViti, 249 Rewa Street, Fiji. � diyarash@gmail.com https://orcid.org/0000-0002-7699-9549 Abstract Available information on Gynacantha Rambur, 1842 species from the South Pacific is reviewed. Specimens were found to be sufficiently similar to G. rosenbergi Kaup in Brauer, 1867 to be placed in the same species group (G. rosenbergi group—established here) but also distinct enough to form a subgroup of its own (G. rosenbergi Pacific group). All species of the G. rosenbergi group are diagnosed, with three species, Gynacantha vitiana sp. n. (male and female) from Viti Levu, Fiji, G. koroana sp. n. (male) from Koro, Fiji and G. vanuatua sp. n. (male) from Malekula, Vanuatu being described as new to science. A key is presented for identification of the males. Key words: Gynacantha, South Pacific, Fiji, Vanuatu, new species Introduction Because of the crepuscular behaviour of adults, specimens of Gynacantha Rambur, 1842 species are not abundant in collections, and there is limited information on the genus, particularly for species from the Pacific islands. Brauer (1864) was the first to mention the presence of Gynacantha on the islands of the South Pacific when he recorded Gynacantha sp. (a broken specimen) from the Society Islands of French Polynesia. However, this record is actually Anaciaeschna jaspidea (Burmeister, 1839) as discussed in Marinov et al. (2019). Therefore it was Fraser (1927) who first legitimately recorded the genus from the South Pacific, describing G. apiaensis from Samoa and G. stevensoni from Tonga. Subsequently, only Gynacantha rosenbergi Kaup in Brauer, 1867 was generally recorded from throughout the islands in the South Pacific: Kimmins (1936) from Vanuatu, Lieftinck (1949) from Solomon Islands, Lieftinck (1975) and Bryan (1924) from Fiji, and Kimmins (1953), Dommanget (2000), Davies (2002) and Grand et al. (2014, 2019) from New Caledonia. Only Van Gossum et al. (2006) reported G. sp. cf. stevensoni from Fiji, and Donnelly (1986) reported G. apiaensis from Samoa. Additionally, personal observations of G. rosenbergi have been communicated by J. Barrault, and D. Grand (from New Caledonia), by K. Lovich (from Koro) and by T. Donnelly, who was referring to G. stevensoni (from Fiji). In order to better resolve our understanding of Gynacantha throughout the South Pacific islands, this hotch- potch of information strongly suggested the need to re-examine the types for both G. apiaensis and G. stevensoni and compare them with the apparently similar G. rosenbergi and its close allies and with all other Gynacantha specimens currently available from the Pacific islands.