Disertasia disticha ( Bosc, 1802 ) Calder & Faucci, 2021

Calder, Dale R. & Faucci, Anuschka, 2021, Shallow water hydroids (Cnidaria, Hydrozoa) from the 2002 NOWRAMP cruise to the Northwestern Hawaiian Islands, Zootaxa 5085 (1), pp. 1-73 : 30-31

Disertasia disticha ( Bosc, 1802) , comb. nov.

Fig. 9c

Sertularia disticha Bosc, 1802: 101 , pl. 29 fig. 2.

Dynamena cornicina .— Cooke, 1977: 95, fig. 21.— Coles et al., 2002a: 207; 2004: 73.— Carlton & Eldredge, 2009: 38.

Type locality. Atlantic Ocean: “...sur le fucus natans ( Sargassum natans ) dans la haute mer…” ( Bosc 1802: 101, as Sertularia disticha ).

Voucher material. Pearl & Hermes Atoll , on algae, 28.ix.2002, one colony, 9 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5428 .

Remarks. This hydroid conforms with traditional taxonomic accounts of Dynamena disticha ( Bosc, 1802) , and it has been provisionally assigned to that species here. However, evidence from both morphology and DNA barcoding ( Moura et al. 2011) indicates the likely existence of a species complex under that name. The hydroid from Pearl & Hermes Atoll may be specifically distinct from that of Bosc, and changes in nomenclature might be expected.

The species of Bosc (1802) was described from material collected on pelagic Sargassum in the open Atlantic Ocean. Colonies from that substrate are small (1 cm high or less), gracile, and unbranched ( Calder 1991a). Another morphotype from a variety of substrates along the shallow Atlantic coast are larger in size (up to 5 cm high), more robust, and an essentially perpendicular branch may infrequently be present ( Fraser 1944, as Sertularia cornicina ; Calder 1971, as Dynamena cornicina ). The overall morphology of their trophosomes and gonosomes are otherwise much alike, and the colour of both is bright yellow. Comparisons of them are warranted to establish if observed differences are attributable to genetics or environment.

Molecular studies by Moura et al. (2011), Maronna et al. (2016), and Song (2019) confirm that Dynamena Lamouroux, 1812 is polyphyletic. Indeed, Dy. disticha has been shown by them in all phylograms to be genetically distant from Sertularia pumila Linnaeus, 1758 , type species of the genus. The species also appears too remote from Tridentata Stechow, 1920 , type species Sertularia perpusilla Stechow, 1919b , to be assigned there. Instead, as noted above, the genus Disertasia Neppi, 1917 has been resurrected here from the synonymy of Dynamena to accommodate this and closely related species. Of particular note, the type species of Disertasia by monotypy, Di. cavolini Neppi, 1917 , is taken to be conspecific with Dy. disticha ( Picard 1958; Calder 1991a; Medel & Vervoort 1998; Gravili et al. 2015). The present species is thus assigned the binomen Disertasia disticha , comb. nov. Also assigned here to Disertasia , based on their proximity in molecular phylograms to Di. disticha , are Dy. moluccana ( Pictet, 1893) and, with somewhat less certainty, Dy. crisioides Lamouroux, 1824 . Meanwhile, it is unclear if any of the sampled populations of Di. disticha included in molecular analyses were from pelagic Sargassum , as with the original account of the species by Bosc (1802).

In an obscure paper on hydroid epibionts from pelagic Sargassum in the North Atlantic, Bosc (1797) described, as Hydra quinternana , a small yellow sertulariid likely to have been identical with Disertasia disticha . It therefore constitutes a nomenclatural threat to the now widely used species name Dy. disticha (= Sertularia disticha Bosc, 1802 ). In the interests of nomenclatural stability, Reversal of Precedence provisions in the code (ICZN 1999, Art. 23.9) are followed here to designate Di. disticha ( Bosc, 1802) as valid and a nomen protectum, and to relegate H. quinternana Bosc, 1797 to a nomen oblitum. Reversal of Precedence is applicable in this case because the binomen H. quinternana has not been used as a valid name in zoology after 1899, while Dy. disticha has appeared in more than 25 publications by numerous authors (>10) in the past 50 years (e.g., Boero 1981; Calder 1991a, 1995, 2013, 2019; Cornelius 1992; Migotto 1996; Grohmann et al. 1997; Medel & Vervoort 1998; Faucci & Boero 2000; Peña Cantero & García Carrascosa 2002; Kirkendale & Calder 2003; Schuchert 2003; Calder & Kirkendale 2005; Bouillon et al. 2006; Vervoort 2006; Gravier-Bonnet 2007; Galea 2008, 2010; Cunha & Jacobucci 2010; Moura et al. 2011; Xu et al. 2014b; Galea & Ferry 2015; Gravili et al. 2015; Oliveira et al. 2016; Maronna et al. 2016; MendozaBecerril et al. 2018; Miglietta et al. 2018).

For much of the 20 th century, this species was assigned to Dynamena cornicina (= Sertularia cornicina McCrady, 1859). The actual identity of Dy. cornicina is ambiguous at present, however, and its binomen is now taken to be a nomen dubium. McCrady’s (1859) original description of the species, from Charleston Harbor, South Carolina, USA, was lacking in detail, no illustrations of it were provided, and no types are known to exist. His account applies equally to two abundant species in the Charleston area ( Calder 1991a), Di. disticha and Amphisbetia distans (= Dynamena distans Lamouroux, 1816 ). As for hydroids assigned to Dy. cornicina auct. during the period, most are taken to have been identical with Di. disticha rather than A. distans . Specimens identified as Sertularia cornicina from Charleston exist in collections at the MCZ (MCZ IZ 175, MCZ IZ 176), but they were collected by Louis Agassiz rather than John McCrady (Adam Baldinger, personal communication, 15 April 2021). The identity of S. cornicina may therefore be suspected, but not unequivocally proven, from those collections.

Reported Distribution. Hawaiian archipelago. Oahu: Kaneohe Bay, Coconut Point ( Cooke 1977, as Dynamena cornicina ).—Kauai: Nawiliwili main dock, concrete pier pilings; Port Allen main dock, concrete pier pilings ( Coles et al. 2004, as Dy. cornicina ).—Molokai: Kaunakakai Harbor main dock, main pier, concrete pier pilings ( Coles et al. 2004, as Dy. cornicina ).—Maui: Kahului Harbor, Pier 1, concrete pilings ( Coles et al. 2004, as Dy. cornicina ).

Elsewhere. Reported to be circumglobal in shallow waters, from tropical to temperate zones ( Calder 2013).

Figures

FIGURE 9. Sertulariidae. a, Disertasia crisioides (Lamouroux, 1824), part of hydrocladium with three hydrothecal pairs, Gardner Pinnacles, ROMIZ B5427. Scale equals 0.2 mm. b, Disertasia crisioides (Lamouroux, 1824), gonotheca, Gardner Pinnacles, ROMIZ B5427. Scale equals 0.2 mm. c, Disertasia disticha (Bosc, 1802), part of hydrocaulus with three hydrothecal pairs, Pearl & Hermes Atoll, ROMIZ B5428. Scale equals 0.2 mm. d, Pasya heterodonta (Jarvis, 1922), proximal end of hydrocaulus, with three hydrothecal pairs, Pearl & HermesAtoll, ROMIZ B5436. Scale equals 0.2 mm. e, Pasya heterodonta (Jarvis, 1922), distal end of hydrocaulus, with three hydrothecal pairs, two pairs being stacked, Kure Atoll, ROMIZ B5491. Scale equals 0.2 mm. f, Pasya heterodonta (Jarvis, 1922), distal end of hydrocaulus, with three stacked hydrothecal pairs, Pearl & Hermes Atoll, ROMIZ B5485. Scale equals 0.2 mm. g, Pasya heterodonta Jarvis, 1922), gonotheca, Kure Atoll, ROMIZ B5491. Scale equals 0.1 mm. h, Salacia tetracythara Lamouroux, 1816, part of hydrocladium with three hydrothecal pairs, Lisianski Island, ROMIZ B5429. Scale equals 0.2 mm. i, Salacia tetracythara Lamouroux, 1816, gonotheca from same colony, Lisianski Island, ROMIZ B5429. Scale equals 0.2 mm.