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 Pasya heterodonta ( Jarvis, 1922 ) , comb. nov. Fig. 9d–g Pasythea heterodonta Jarvis, 1922: 344 , pl. 24 figs 11A–B, 12. Type locality. Republic of Mauritius : Cargados (=Cargados Carajas Shoals), 24 fm ( 44 m ) ( Jarvis 1922 ) . Voucher material. Pearl & Hermes Atoll , on calcareous rubble, 28.ix.2002 , three colonies, to 9 mm high, without gonothecae, coll. A. Faucci , ROMIZ B5436 .— Midway Atoll , on Halimeda sp. , 20.ix.2002 , one colony, 8 mm high, without gonothecae, coll. A. Faucci , ROMIZ B5437 .— Pearl & Hermes Atoll , 19.ix.2002 , three colony fragments, 8.5 mm high, without gonothecae, coll. A. Faucci , ROMIZ B5438 .— Pearl & Hermes Atoll , on calcareous rubble, 19.ix.2002 , one colony, 8 mm high, without gonothecae, coll. A. Faucci , ROMIZ B5485 .— Kure Atoll , on calcareous rubble, 25.ix.2002 , five colonies or colony fragments, to 9 mm high, with gonothecae, ROMIZ B5491 . Remarks. Pasya heterodonta ( Jarvis, 1922 ) resembles the much better-known P. quadridentata (Ellis & Solan-der, 1786) in having stacked hydrothecal pairs on the stems ( Fig. 9e, f ). It differs, however, in having stacked pairs only at the extreme distal ends the cauli. Indeed, such groups are sometimes entirely lacking in present material, likely occurring in younger and earlier developmental stages of a given caulus. While gonothecae of the two species are fundamentally alike, suggestive of a close relationship, those of P. heterodonta appear to have fewer and less pronounced ridges. Grouping of hydrothecal pairs may occasionally occur as well in P. obliqua ( Lamouroux, 1816 ) , but hydrothecae of that species are more swollen and internodes are much shorter and stouter. In reporting P. heterodonta from Moorea, French Polynesia , Vervoort & Vasseur (1977 , as Dynamena heterodonta ) provided a description and illustrations of type material of the species. Unlike in P. quadridentata , hydrothecae were said to have a longer free portion that curved away from the internode, the operculum was more acute, and intrathecal cusps were well-developed. Similar differences in hydrothecal morphology had convinced Billard (1925) earlier to recognize P. heterodonta as distinct from P. quadridentata . Gibbons & Ryland (1989) acknowledged the distinct appearance of two equivalent morphotypes from Fiji , but nevertheless questioned the validity P. heterodonta . They suggested that perceived differences might not exceed the range of morphological variability within P. quadridentata . Given its distinct morphology, including the relative paucity of contiguous hydrothecal groups and their limitation to the distal end of the stems, P. heterodonta is taken here to be a species of the tropical Indo-Pacific, distinct from P. quadridentata ( type locality: “...coast of Africa, not far from the island of Ascension ”). Pasya heterodonta has also been recognized recently as valid by Galea (2016 , as Dynamena heterodonta ) in material from Indonesia . Cauli of P. heterodonta lacking stacked pairs of hydrothecae closely resemble those of both Thuiaria maldivensis Borradaile, 1905 and Sertularia borneensis Billard, 1925 . Given their similarity, Schuchert (2003) suspected that the latter two might be conspecific. While gonothecae of T. maldivensis are still undescribed, Gibbons & Ryland (1989) and Schuchert (2003) provided descriptions and illustrations of gonothecae of S. borneensis based on specimens from Verde Island, the Philippines , and the Kei Islands, Indonesia , respectively. They differ from those of P. heterodonta in being strongly ridged. Moreover, Gibbons and Ryland noted the existence of two lateral horns that arose from a distal gonothecal collar, as in species assigned to Tridentata Stechow, 1920 ( type species S. perpusilla Stechow, 1919b ). As for Pasya Stechow, 1922 , the genus has recently been resurrected as valid ( Calder 2013 ) given the genetic distance of its type species, Sertularia quadridentata ( Ellis & Solander, 1786 ) , from that of Sertularia pumila Linnaeus, 1758 , type species of a currently polyphyletic genus Dynamena Lamouroux, 1816 . The extent of their separation is apparent in phylograms such as those of Moura et al . (2011) and Song (2019). Pasya was proposed by Stechow (1922) as a replacement name for use in Hydrozoa of Pasythea Lamouroux, 1812 ( type species: Cellaria tulipifera Ellis & Solander, 1786 ), now restricted to Bryozoa. Tuliparia de Blainville, 1830 has the same type species ( Stechow 1922 ) and is a junior objective synonym of Pasythea . Development of the intrathecal cusps varied considerably within colonies of P. heterodonta examined here ( Fig. 9d–f ). Disparities in their development were noted earlier by Billard (1925) and are apparent in illustrations of the species by Galea (2016 : fig. 1L, N). Only slight variations in cusp development were noted by Vervoort & Vasseur (1977) . Reported Distribution. Hawaiian archipelago. First record. Elsewhere. French Polynesia : Tuamotu Archipelago, Gambier Island ( Billard 1905 , as Sertularia gracilis ).— Indonesia : Makassar Strait, 2°25ʹS , 117°43ʹE ; E of Sumbawa, 34–36 m , Billard 1925, as Dynamena heterodonta ).— New Caledonia : Ile des Pins ( Redier 1966 , as D. heterodonta ; Gravier Bonnet 2007, as D. heterodonta ).— South Africa ( Millard 1975 , as Dynamena quadridentata , in part, Fig. 87H).—Moorea ( Vervoort & Vasseur 1977 , as D. heterodonta ).— Fiji ( Gibbons & Ryland 1989 , as D. quadridentata , type B).— Indonesia : Arafura Sea ( Galea 2016).