Halopteris longibrachia, 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 : 45-46

Halopteris longibrachia , nom. nov.

Fig. 13g –i

Plumularia polymorpha var. sibogae Billard, 1913: 25 , fig. 16.

Type locality. Indonesia: Raja Ampat , 1°42.5’S, 130°47.5’E, 32 m ( Billard 1913) .

Voucher material. Gardner Pinnacles, on rubble, 14.ix.2002, two colonies or colony fragments, to 1.5 cm high, with gonothecae, coll. A. Faucci, ROMIZ B5459.—Gardner Pinnacles, on Macrorhynchia phoenicea , 14.ix.2002, two colonies, to 7 mm high, without gonothecae, coll.A. Faucci, ROMIZ B5460.—Pearl & Hermes Atoll, 19.ix.2002, four colonies or colony fragments, to 1.7 cm high, one colony with female gonothecae, coll. A. Faucci, ROMIZ B5461.

Etymology. The replacement specific name longibrachia is derived from the Latin words longus, meaning long, and brachium, meaning arm, in reference to the exceptionally long, arm-like lateral nematothecae that distinguish this species.

Remarks. Originally described as Plumularia polymorpha var. sibogae Billard, 1913 , this species was recently elevated to species rank by Galea et al. (2018), as Halopteris sibogae ( Billard, 1913) . The species is a morphologically striking one in having unusually long lateral nematothecae that extend well beyond the rim of the hydrothecae. Other morphological differences setting it apart from H. polymorpha Billard, 1913 include an interesting colour difference in living specimens ( Galea et al. 2018). While hydranths of H. polymorpha are yellow everywhere, those of the so-called H. sibogae are mostly yellow on the stems but white on the cladia. The distinctness of the species has been further confirmed by 16S DNA sequences ( Galea et al. 2018). It occurs in a clade well-separated from H. polymorpha and close to H. vervoorti Galea, 2008 .

Nomenclaturally, however, Plumularia polymorpha var. sibogae (= Plumularia sibogae ; Halopteris sibogae ) is a permanently invalid junior primary homonym of Plumularia sibogae Billard, 1911 , a different species now assigned to Antennella Allman, 1877 (ICZN, 1999, Art. 57.2). With no available and potentially valid synonyms in existence for the rejected junior primary homonym Plumularia sibogae , Halopteris longibrachia is proposed here as a new replacement name for it.

Other halopteridids with exceptionally long lateral nematothecae and nematothecal apophyses include Corhiza valdiviae ( Stechow, 1925) , assigned to the new genus Thamnopteros by Galea, in Galea & Maggioni, 2020, and T. uniserius Galea , in Galea & Maggioni, 2020. However, colonies of the latter two differ greatly from those of H. longibrachia in being much larger (to 40 cm in T. valdiviae ; to 17.2 cm in T. uniserius ; to 2.5 cm high in H. longibrachia ) and in having polysiphonic stems ( Stechow 1925; Millard 1975; Schuchert 1997, Galea, in Galea & Maggioni 2020). Other characters distinguishing T. valdiviae , reported from South Africa and Mozambique, are provided by Stechow (1925), Millard (1975), and Schuchert (1997). Characters distinguishing T. uniserius , described from New Caledonia, have been summarized by Galea, in Galea & Maggioni (2020). Halopteris infundibulum Vervoort, 1966 also has a pair of long lateral nematothecae, but adjacent to each one, at the base of the same apophysis, is a smaller, much shorter nematotheca. Its hydrocladia differ in appearing essentially unsegmented. The species is known from bathyal depths off New Zealand, the Chatham Islands, and New Caledonia ( Vervoort 1966; Vervoort & Watson 2003; Ansín Agís et al. 2009).

Although H. longibrachia ranges at least from the Seychelles ( Millard & Bouillon, 1973, as H. polymorpha var. sibogae ) to the Hawaiian Archipelago (this report), it has been reported infrequently. The type material of Billard (1913, as Plumularia polymorpha var. sibogae ) consisted of two colonies from Raja Ampat, Indonesia, collected during the Siboga Expedition. Schuchert (1997 , as H. polymorpha var. sibogae ) examined those types, along with specimens from the Seychelles reported by Millard & Bouillon. Horia Galea collected numerous fertile colonies from two shipwrecks at Bali, Indonesia ( Galea et al. 2018, as H. sibogae ). Others examined in the same report were found on a reef north of Hoga Island in the Tukang Besi Archipelago, Indonesia, by G. Allard. A record from Japan by Hirohito (1983, as H. polymorpha var. sibogae ) has been viewed with uncertainty ( Galea et al. 2018). Specimens examined here from the Northwestern Hawaiian Islands were found at Gardner Pinnacles and Pearl & Hermes Atoll.

Reported Distribution. Hawaiian archipelago. First record.

Elsewhere. Western Pacific ( Galea et al. 2018, as Halopteris sibogae ); Indian Ocean ( Millard & Bouillon 1973, as H. polymorpha var. sibogae ).

Figures

FIGURE 13. Kirchenpaueriidae and Halopterididae. a, Pycnotheca producta (Bale, 1881), part of a hydrocladium with two hydrothecae, Laysan Island, ROMIZ B5481. Scale equals 0.1 mm. b, Antennella secundaria (Gmelin, 1791), part of hydrocaulus with two hydrothecae, Midway Atoll, ROMIZ B5454. Scale equals 0.1 mm. c, Antennella secundaria (Gmelin, 1791), part of a colony to show branching, Midway Atoll, ROMIZ B5455. Scale equals 0.5 mm. d, Antennella secundaria (Gmelin, 1791), part of hydrocaulus, and base of a hydrocladium with a hydrotheca, Midway Atoll, ROMIZ B5455. Scale equals 0.1 mm. e, Halopteris alternata (Nutting, 1900), part of a hydrocladium with two hydrothecae, Laysan Island, ROMIZ B5458. Scale equals 0.1 mm. f, Halopteris alternata (Nutting, 1900), part of hydrocaulus, with a cauline hydrotheca and proximal end of a hydrocladium, Laysan Island, ROMIZ B5458. Scale equals 0.1 mm g, Halopteris longibrachia, nom. nov., part of a hydrocladium with two hydrothecae, Gardner Pinnacles, ROMIZ B5459. Scale equals 0.1 mm. h, Halopteris longibrachia, nom. nov., female gonotheca, Pearl & Hermes Atoll, ROMIZ B5461. Scale equals 0.1 mm. i, Halopteris longibrachia, nom. nov., part of hydrocaulus with a male gonotheca, Gardner Pinnacles, ROMIZ B5459. Scale equals 0.1 mm.