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 Monotheca flexuosa ( Bale, 1894 ) Fig. 11a Plumularia flexuosa Bale, 1894: 115 , pl. 5 figs 6–10. Monotheca flexuosa .— Calder, 2020: 225 , fig. 7d–f. Type locality. Australia : Victoria , “mouth of Snowy River and Cape Lefebvre ” ( Bale 1894 , as Plumularia flexuosa ) . Voucher material. Kure Atoll, on algae, 26.ix.2002 , one colony, 2.5 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5447. Remarks. Originally described from Australia , Monotheca flexuosa ( Bale, 1894 ) was recently reported in the central North Pacific from the main Hawaiian Islands of Oahu and Maui ( Calder 2020 ). While its overall distribution is still uncertain, Watson (2011a) suspected that the species might be cosmopolitan. In having slender colonies and cup-shaped hydrothecae with essentially straight margins, M. flexuosa resembles M. margaretta Nutting, 1900 , the type species of Monotheca Nutting, 1900 . Unlike in M. margaretta , however, its stems are more flexuous, lateral nematothecae appear sessile rather than pedicellate, and hydrothecae lack a median adaxial notch. Another similar species is M. pulchella ( Bale, 1881 ) , but its stem is robust with stronger perisarcal ridges, and hydrocladia arise midway along much shorter cauline internodes ( Bale 1894 ; Watson 2011a ). As for M. obliqua ( Johnston, 1847 ) , its margin is more sinuous, and female gonothecae appear to be smooth ( Cornelius 1995b ) rather than transversally ridged, as in M. margaretta ( Calder 1997 ) , or smooth to faintly undulated, as in M. flexuosa ( Watson 2011a ) . Evidence for recognition of Monotheca as distinct from Plumularia Lamarck, 1816 has been made elsewhere on the basis of both morphology ( Calder 1997 ) and genetics ( Moura et al . 2018 ). Species currently assigned to the genus are small and often epiphytic, although M. obliqua , M. flexuosa , M. margaretta , and M. bergstadi Gil & Ramil, 2021 are or appear to be substrate generalists ( Watson 2011a ; Gravili et al . 2015 ; Calder 2019; Gil & Ramil, 2021 ). Reported Distribution. Hawaiian archipelago. Oahu: Palea Point, just outside Hanauma Bay, 8 m ( Calder 2020 ). — Maui: Kanaio, 12 m ( Calder 2020 ). Elsewhere. Australia ( Watson 2011a ); Japan ( Hirohito 1974 , as Monotheca flexiosa ); New Zealand ( Vervoort & Watson 2003 , as M. pulchella );? South Africa ( Stechow 1925 ; Millard 1975 , as M. pulchella );?Strait of Gibraltar ( Medel & Vervoort 1995 , as M. pulchella );?Vema Seamount ( Millard 1966b , as M. pulchella ).