Campanularia brevithecata Thornely, 1900: 454 Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern Hawaiian Islands Calder, Dale R. Faucci, Anuschka Zootaxa 2021 2021-12-24 5085 1 1 73 8TG5C (Thornely, 1900) Thornely 1900 [151,593,1770,1797] Hydrozoa Campanulariidae Clytia Animalia Leptothecata 15 16 Cnidaria species brevithecata   Fig. 5a      Campanularia brevithecata Thornely, 1900: 454, pl. 44 figs 8, 8a, b.     Typelocality. Papua New Guinea: New Britain, Blanche Bay( Thornely 1900, as  Campanularia brevithecata).  Vouchermaterial. Nihoa, on calcareous rubble,  06.x.2002, one colony, 1.25 mmhigh, without gonothecae, coll. A. Faucci, ROMIZ B5414.—  Pearl& Hermes Atoll, on  Halimedasp.,  19.ix.2002, one colony, 3 mmhigh, without gonothecae, ROMIZ B5480.   Remarks.The hydroid of  Clytia brevithecata( Thornely, 1900), typelocality Papua New Guinea, appears indistinguishable morphologically from that of  Clytia hummelincki( Leloup, 1935), typelocality 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. hummelinckifrom Agulhas Bank at the southern tip of Africa. Based on morphology, the two are taken here to be conspecific, with the name  C. brevithecatahaving 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. hummelinckifrom South Africa, Italy, and Belizeare 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. hummelinckihave 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 Clytiidaeand the genus  Clytia. The hydrozoan assigned the binomen  C. hummelinckihas 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 thcentury. From the original description of the species in the Caribbean Sea ( Leloup 1935), its reported range now extends to the FloridaKeys, USA( Deevey 1954), Ghana, west Africa ( Buchanan 1957, as  Laomedea hummelincki), Agulhas Bank, South Africa( Millard 1966a, 1975), Bermudaand 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. hummelinckifrom 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). 4523879309 2002-10-06 Papua New Guinea Blanche Bay Nihoa Voucher 15 16 1 West New Britain holotype 4523879352 [151,511,150,177] ROMIZ A. Faucci 16 17 B5414 1 4523879395 2002-09-19 ROMIZ Pearl & Hermes Atoll 16 17 B5480 1