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 elsaeoswaldae Stechow, 1914 Fig. 5b, c Clytia elsae-oswaldae Stechow, 1914: 125 , fig. 4. Clytia cf. gracilis .— Coles et al ., 2009: 59 , 68, 72, 76, 82, 85 [not Clytia gracilis (M. Sars, 1850 ) ]. Clytia elsaeoswaldae .— Calder, 2020: 208 , fig. 2b, c. Type locality. Virgin Islands of the United States: St. Thomas , port of Charlotte Amalie ( Stechow 1914 ) . Voucher material. Midway Atoll , on algae, 23.ix.2002 , one colony, 2 mm high, with a gonotheca, coll. A. Faucci , ROMIZ B5415 . Remarks. Hydroids from our collections corresponded closely with original descriptions of two warm-water species of the genus Clytia Lamouroux, 1812 , C. obliqua ( Clarke, 1907 ) and C. elsaeoswaldae Stechow, 1914 . Colonies of both appear to be stolonal or mostly so rather than erect and branched, hydrothecae are relatively broad with rounded bases, and hydrothecal cusps slant to the right rather than being regularly triangular when viewed laterally ( Clarke 1907 ; Stechow 1914 ; Lindner et al . 2011 ; Cunha et al . 2020 ). Gonothecae were lacking in Clarke’s (1907) specimens of C. obliqua , but those of C. elsaeoswaldae had smooth to slightly undulating walls, a constriction below the truncated distal end, and they usually arose from the hydrorhiza ( Lindner et al . 2011 ; Stechow 1914 ). Such characters correspond with material examined here. From these descriptions the two species seem much alike and, if conspecific, the binomen C. obliqua would have priority. FIGURE 5. Clytiidae . a, Clytia brevithecata ( Thornely, 1900 ) , hydrotheca and pedicel, Nihoa, ROMIZ B5414. Scale equals 0.2 mm. b, Clytia elsaeoswaldae Stechow, 1914 , hydrotheca and pedicel, Midway Atoll, ROMIZ B5415. Scale equals 0.1 mm. c, Clytia elsaeoswaldae Stechow, 1914 , gonotheca, Midway Atoll, ROMIZ B5415. Scale equals 0.1 mm. d, Clytia linearis ( Thornely, 1900 ) , hydrotheca and distal end of pedicel, Gardner Pinnacles, ROMIZ B5418. Scale equals 0.2 mm. e, Clytia linearis ( Thornely, 1900 ) , gonotheca, Laysan Island, ROMIZ B5417. Scale equals 0.2 mm. f, Clytia cf. noliformis ( McCrady, 1859 ) , hydrotheca and pedicel, Pearl & Hermes Atoll, ROMIZ B5419. Scale equals 0.2 mm. g, Clytia cf. noliformis ( McCrady, 1859 ) , hydrotheca and distal end of pedicel, Pearl & Hermes Atoll, ROMIZ B5419. Scale equals 0.1 mm. However, the identity of C. obliqua is uncertain based on subsequent accounts of the species. After examining type material of the species, Cornelius (1982) concluded that it was conspecific with C. linearis ( Thornely, 1900 ) . That synonymy was followed in several other works (e.g., Gibbons & Ryland 1989 ; Calder 1991a ; Watson 2000 ; Xu et al . 2014b ; Wedler 2017 ; Choong et al . 2019). However, unlike material examined here, hydroids of C. linearis are mostly erect and branched, and their hydrothecal cusps are slender and regularly triangular, with an internal keellike thickening of perisarc. Meanwhile, Gibbons & Ryland (1989) discussed the identity of a hydroid from Fiji that closely resembled Clarke’s (1907) illustration of C. obliqua (although hydrothecal cusps were shown with a slant to the left rather than the right in their illustrations). They nevertheless followed Cornelius (1982) in concluding that C. obliqua was conspecific with C. linearis , and identified their hydroids as C .? gracilis instead. A syntype of C. obliqua (USNM 29616) examined during their deliberations was said to be branched, with tall hydrothecae. That seems at least somewhat at variance with the original account of Clarke (1907) , who described the species as “…a small creeping form with peduncles from 1 mm to 1½ mm in height.” The specimens portrayed in Clarke’s illustrations were stolonal, and hydrothecae were not particularly deep. Moreover, unlike in C. linearis , Gibbons & Ryland observed no keel-like thickening on the inner edge of the cusps in the type. Given the conflicting accounts of C. obliqua , along with the lack of gonophores in Clarke’s material, the species is regarded here as a species inquirenda . The type of C. obliqua at the NMNH was unavailable for examination during this study because of the pandemic outbreak in 2019. Hydroids examined here have therefore been assigned to C. elsaeoswaldae . Clytia elsaeoswaldae is morphologically close to the much better-known C. gracilis (M. Sars, 1850 ) , type locality Lofoten, Norway . Progress has been made in distinguishing the tropical to warm-temperate C. elsaeoswaldae from the boreal C. gracilis based on characters noted above ( Lindner et al . 2011 ; Cunha et al . 2020 ). Records of C. gracilis from the tropical Pacific Ocean, including the Hawaiian Islands ( Coles et al . 2009 ), are therefore believed to have been based on misidentifications of the present species. Its is likely much more widespread than currently recognized. Reported Distribution. Hawaiian archipelago. Oahu: Pearl Harbor, West Loch entrance channel ( Coles et al . 2009 , as Clytia cf. gracilis ; Calder 2020 ); Pearl Harbor, Hospital Point South ( Coles et al . 2009 , as C. cf. gracilis ); Pearl Harbor, Rainbow Bay Marina , floating buoys and docks ( Coles et al . 2009 , as C. cf. gracilis ; Calder 2020 ); Keehi Lagoon, marina docks ( Coles et al . 2009 , as C. cf. gracilis ); Pearl Harbor, Rainbow Bay Marina , < 1 m , on dock ( Calder 2020 ). Elsewhere. Tropical and warm-temperate waters of the western Atlantic, including the Caribbean Sea ( Stechow 1914 ; Lindner et al . 2011 ; Calder 2019) and the warm eastern Pacific ( Bryant & Arehart 2019 , medusa stage). If C. obliqua is conspecific, the species has also been reported from Panama , Pacific coast ( Clarke 1907 ), Japan ( Fraser 1936 ; Hirohito 1969 , 1995 ), California , USA ( Fraser 1948 ), and Ecuador ( Calder et al . 2019 ). A report of C. obliqua from the Mediterranean coast of France ( Picard 1950 ) seems questionable.