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 Pycnotheca producta ( Bale, 1881 ) Fig. 13a Plumularia producta Bale, 1881: 39 , pl. 15 fig. 3. Type locality. Australia : Victoria , Queenscliff ( Bale 1881 ) . Voucher material. Laysan Island, on algae, 13.ix.2002 , four colonies or colony fragments, to 6 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5481. Remarks. The generic name Pycnotheca Stechow, 1919b was proposed as a replacement name for Diplocheilus Allman, 1883 , an invalid junior homonym of Diplocheilus van Hasselt & Temminck, 1823 (Pisces) . The type species of the genus, by subsequent designation by Stechow (1923c: 215) , is Diplocheilus mirabilis Allman, 1883 . Molecular phylogenetic studies ( Maronna et al . 2016 ; Moura et al . 2018 ) confirm the close phylogenetic relationship of Pycnotheca to kirchenpaueriid genera including Kirchenpaueria Jickeli, 1883 and Oswaldella Stechow, 1919a . Watson (1990) provided a review of characters useful in distinguishing the three currently recognized species of Pycnotheca . Pycnotheca mirabilis ( Allman, 1883 ) differs from P. producta ( Bale, 1881 ) and P. biseptata ( Blackburn, 1938 ) in having stems that are longer (up to 35 mm rather than to 10–15 mm ), hydrocladia that arise at a more acute angle and are both long and flexuous rather than short and stiffer, hydrothecae that are decidedly scoop-shaped rather than jug- or bowl- shaped, and gonothecae that are large and usually erect rather than small and typically adherent to the hydrorhiza or substrate. In life, hydranths of P. producta were said by Watson to be a luminescent bluish–white in colour. Pycnotheca biseptata differs from both P. mirabilis and P. producta in having a rudimentary septal ridge passing from the hydrocladial internode into the adcauline wall of the hydrotheca. Watson also provided measurements of major morphological characters of each species. In terms of substrate preferences, P. mirabilis was reported by Vervoort & Watson (2003) to be predominantly an epizoite and P. producta an epiphyte. Nonetheless, Vervoort & Watson noted that differences between P. producta and P. mirabilis were not clearly resolved. If the two should prove conspecific, the name P. producta was described first and would have nomenclatural priority. Based on Watson’s (1990) characterization of the three species, specimens from Laysan most closely correspond with P. producta and have been assigned to that species here. The geographic distribution of P. producta is uncertain because it and P. mirabilis may have been confused in some works ( Watson 1990 ). To date, the species has been reported from locations in both the western and eastern Pacific, although the report of it from California by Torrey (1902 , as Halicornaria producta ) needs confirmation. If P. mirabilis is conspecific, the range of the species is extended to many locations across the Indo-west Pacific ( Ansín Agís et al . 2014 ), as well as to False Bay, South Africa ( Millard 1957 ), Vema Seamount ( Millard 1966b ), and Brazil ( Oliveira et al . 2016 ) in the Atlantic. The publication of Bale (1881) in which P. producta was first described is usually dated as 1882. Evidence exists that it appeared as a separate in 1881 (see comment in References section). Reported Distribution. Hawaiian archipelago. First record. Elsewhere. Australia ( Bale 1881 , as Plumularia producta ; Watson 1990 , 1997); Japan ( Inaba 1892 , as P. producta );? California , USA ( Torrey 1902 , Halicornaria producta ).