Accepted by A. Collins: 27 Feb. 2017; published: 3 Apr. 2017 ZOOTAXA ISSN 1175-5326 (print edition) ISSN 1175-5334 (online edition) Copyright © 2017 Magnolia Press Zootaxa 4250 (1): 043–054 http://www.mapress.com/j/zt/ Article 43 https://doi.org/10.11646/zootaxa.4250.1.3 http://zoobank.org/urn:lsid:zoobank.org:pub:E127AE48-36C8-4A36-95D0-CCC65B1FC4D0 A new species of clausophyid calycophoran siphonophore (Cnidaria: Hydrozoa), Kephyes hiulcus sp. nov., widely distributed throughout the world's oceans MARY MATILDA GROSSMANN 1,3 & DHUGAL JOHN LINDSAY 2 1 Marine Biophysics Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna, Okinawa, 904- 0495 Japan 2 Japan Agency for Marine–Earth Science and Technology (JAMSTEC), Yokosuka, 237-0061 Japan. E-mail: dhugal@jamstec.go.jp 3 Corresponding author. E-mail: grossmann.mary@gmail.com Abstract A new species of clausophyid siphonophore, Kephyes hiulcus sp. nov . is described. It can most easily be differentiated from its congener Kephyes ovata by the shape of the hydroecium in the anterior nectophore of the polygastric stage. This is open over the entire height of the nectophore in K. hiulcus sp. nov ., and it is this character from which its specific name is derived. This species was found in the eastern and western Pacific Ocean, as well as the Celebes and Mediterranean Seas, indicating that this species is both relatively common and geographically widespread. Key words: Clausophyidae, mesopelagic, taxonomy, new species Introduction Clausophyid siphonophores are a conspicuous component of the gelatinous macroplankton community at meso- and bathypelagic depths throughout many of the world's oceans (eg. Mapstone 2009). Because of their relatively large size, most members of this family are easily observable by crewed submersibles and remotely-operated vehicles (Silguero & Robison 2000; Lindsay et al. 2015). A recent review by Pugh (2006) finally sorted out the convoluted taxonomy of the family, erecting a new genus, Kephyes Pugh, 2006, and providing a redescription of Kephyes ovata (Keferstein & Ehlers, 1860). Unfortunately, an oversight in that paper, where an undescribed Kephyes species was inadvertently included in the studied K. ovata material, had gone unrecognized, and this mistake subsequently has been perpetuated (eg. Mapstone 2014). Before the taxonomy of this group once again becomes convoluted, the species Kephyes hiulcus sp. nov ., is described below based on the material of Pugh (2006) and further material from off Japan, the Celebes Sea and the Mediterranean Sea. Materials and methods Material for this study was collected using several different ships and survey platforms around the world over the course of many years (Table 1). The type material was collected at 1189 m in Monterey Canyon by the ROV ‘Tiburon’ (dive T0980-D4, 10 May 2006, 36°36’11.909”N, 122°22’31.998”W). Material from Japan was collected on cruises of the T.R.V. Tokaidaigaku Maru Nisei in Suruga Bay (34°51.0’N, 138°38.3’E) from 1980 to 1992 using a 160 cm-diameter ring net with 2 mm mesh size (Kubota et al., 1992; Kubota & Sawamoto 1993), during the MULTIple Sampling PLAtform Survey of wHole ecosystem (MULTI-SPLASH) cruise in Sagami Bay (35˚0.5'N, 139˚2.0'E) in March 2006, aboard the R.V. Kaiyo (KY06-03) in 2006 using an Intelligent Operated Net Environmental Sampling System (IONESS) net (Kitamura et al. 2001), and during cruises KT10-11, KT11-03 and KT12-07 of the T/V TanseiMaru in Sagami Bay, Japan, from 24–28 June 2010, 8–12 March 2011 and 22–26 April 2012, respectively, using an obliquely-towed ORI net. Further information on the MULTI-SPLASH cruise,