Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern Hawaiian Islands Author Calder, Dale R. Author Faucci, Anuschka 0000-0001-9002-8987 anuschka@hawaii.edu text Zootaxa 2021 2021-12-24 5085 1 1 73 journal article 10.11646/zootaxa.5085.1.1 1175-5326 5802920 12FC3342-F2A0-4EE1-9853-9C5855076A10 Clytia brevithecata ( Thornely, 1900 ) Fig. 5a Campanularia brevithecata Thornely, 1900: 454 , pl. 44 figs 8, 8a, b. Type locality. Papua New Guinea : New Britain , Blanche Bay ( Thornely 1900 , as Campanularia brevithecata ). Voucher material. Nihoa , on calcareous rubble, 06.x.2002 , one colony, 1.25 mm high, without gonothecae , coll. A. Faucci , ROMIZ B5414 .— Pearl & Hermes Atoll , on Halimeda sp. , 19.ix.2002 , one colony, 3 mm high, without gonothecae, ROMIZ B5480 . Remarks. The hydroid of Clytia brevithecata ( Thornely, 1900 ) , type locality Papua New Guinea , appears indistinguishable morphologically from that of Clytia hummelincki ( Leloup, 1935 ) , type locality Bonaire , in the Caribbean Sea. Both have very shallow, cup-shaped hydrothecae with an entire margin, a subhydrothecal spherule, and unbranched pedicels with annulations at the base and occasionally elsewhere. Their gonothecae also seem indistinguishable. Connections between Indo-Pacific and Atlantic populations appear to exist, given Millard’s (1966a , 1975 ) record of C. hummelincki from Agulhas Bank at the southern tip of Africa. Based on morphology, the two are taken here to be conspecific, with the name C. brevithecata having nomenclatural priority. Galea & Ferry (2015: 241) had suggested earlier that the two might be conspecific. Confirmation of their synonymy through DNA studies of topotypic material of the two would be germane. Of note already, however, hydroids identified as C. hummelincki from South Africa , Italy , and Belize are genetically close ( Cunha et al . 2017 ). Synonyms or not, the name of the Pacific species has been adopted for the specimen recorded here from Nihoa. Hydroids identified as C. hummelincki have been shown to be genetically distant from certain other species assigned to Clytia Lamouroux, 1812 . Cunha et al . (2017) debated the ambiguous inclusion of the species in Clytiidae , but its medusa is typical of the group ( Gravili et al . 2008 ) and it has been retained here in both the family Clytiidae and the genus Clytia . The hydrozoan assigned the binomen C. hummelincki has been considered a likely invasive species in the Mediterranean ( Gravili et al . 2008 ). Invasive or not, its known distribution has expanded considerably since the mid-20 th century. From the original description of the species in the Caribbean Sea ( Leloup 1935 ), its reported range now extends to the Florida Keys, USA ( Deevey 1954 ), Ghana , west Africa ( Buchanan 1957 , as Laomedea hummelincki ), Agulhas Bank, South Africa ( Millard 1966a , 1975 ), Bermuda and adjacent banks ( Calder 1991a , 2000 ), Brazil ( Migotto 1996 ; Oliveira et al . 2016 ), the Mediterranean Sea (Boero et al . 1997; Gravili et al . 2008 , 2015 ), the Galapagos Islands ( Calder et al . 2003 ), Papua New Guinea (Boero & Bouillon, unpublished, cited in Gravili et al . 2008 ), Guadeloupe , Martinique , and Panama , in the Caribbean Sea ( Galea 2008 , 2013 ; Miglietta et al . 2018 ), Indonesia ( Di Camillo et al . 2008 ), Cuba ( Castellanos-Iglesias et al . 2009 , 2018), Baa Atoll (Gravier-Bonnet & Bournaud 2012), and Belize ( Cunha et al. 2017 ). A record from Pakistan ( Moazzam & Moazzam 2006 ) was likely based on a misidentification of C. edentula Gibbons & Ryland, 1989 . Records of C. hummelincki from the Indo-Pacific region ( Calder et al . 2003 ; Di Camillo et al . 2008 ; Gravier-Bonnet & Bourmaud, 2012 ; Boero & Bouillon, unpublished) are taken here to have been based on C. brevithecata . Reported Distribution. Hawaiian archipelago. First record. Elsewhere. Circumglobal in tropical and warm-temperate waters (see Remarks above).