Halopteris alternata ( Nutting, 1900 )

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

Halopteris alternata ( Nutting, 1900)

Fig. 13e, f

Plumularia alternata Nutting, 1900: 62 , pl. 4 figs 1, 2.

Halopteris diaphana .— Cooke, 1977: 99, fig. 26.— Carlton & Eldredge, 2009: 36 [not Halopteris diaphana ( Heller, 1868) ]. Halopteris diaphena .— Coles et al., 2004: 73 [incorrect subsequent spelling; not Halopteris diaphana ( Heller, 1868) ].

Type locality. Bahamas: Barracuda Rocks ( Nutting 1900: 62, as Plumularia alternata ) .

Voucher material. Laysan Island , on hydroid stem, 18.ix.2002, two colonies or colony fragments, to 8 mm high, without gonothecae, coll. A. Faucci, ROMIZ B5458 .

Remarks. Hydroids examined here were referable to Halopteris Allman, 1877 , and to the “ H. diaphana ” species group recognized within that genus by Schuchert (1997). Included in the group by him were H. diaphana ( Heller, 1868) , H. tenella ( Verrill, 1873b) , H. alternata ( Nutting, 1900) , H. billardi ( Vannucci, 1951) , and H. platygonotheca Schuchert, 1997 . Halopteris violae Calder et al. 2003 has subsequently been assigned to the same group. Within that assemblage, specimens examined here from Laysan Island are closest to H. alternata . Characters distinguishing the species from others in the cluster have been reviewed by Schuchert (1997) and Calder et al. (2019).

For much of the 20 th century, H. alternata was included in the synonymy of H. diaphana . Confusion over the status of two species was addressed and resolved by Schuchert (1997). He resurrected H. alternata as valid based on its distinctive trophosomal and gonosomal characters. DNA barcoding has confirmed that the two are distinct species ( Moura et al. 2018; Galea et al. 2018). In H. alternata , an axillar nematotheca is usually present behind each cauline hydrotheca, one nematotheca rather than two or three is present on the athecate hydrocladial internodes, and female gonothecae are fusiform and mostly straight rather than cornucopia-shaped. Additional characters distinguishing the two were noted by Ansín Agís et al. (2001). In H. alternata , colonies were often found to be geniculate rather than straight, especially in younger parts. Also, they found segmentation of the hydrocaulus to be homomerous in basal parts but heteromerous in younger and apical parts, rather than being completely heteromerous as in H. diaphana . Halopteris vervoorti Galea, 2008 , another similar species, differs from H. alternata in having paired rather than single cauline axillar nematothecae ( Galea 2008; Galea et al. 2018; Calder 2020).

Halopteris alternata is widely distributed in warm parts of the western North Atlantic ( Oliveira et al. 2016; Calder 2019), and it has been reported as well from the eastern Atlantic ( Ansín Agís et al. 2001). In the Pacific, records of the species exist from Ecuador ( Calder et al. 2019, 2021), and hydroids from Hawaii that have been identified earlier as the mostly European H. diaphana are taken here to have been based instead on H. alternata .

Obvious cryptic diversity has been identified within the H. alternata complex by Moura et al. (2018).

Reported Distribution. Hawaiian archipelago. Oahu: Kaneohe Bay ( Cooke 1977, as Halopteris diaphana ).— Maui: Kahului Harbor, Pier 1 ( Coles et al. 2004, as H. diaphena sic); Kahului Harbor, Pier 2 ( Coles et al. 2004, as H. diaphena sic).

Elsewhere. Western Atlantic ( Oliveira et al. 2016; Calder 2019); eastern Atlantic ( Ansín Agís et al. 2001); eastern Pacific ( Calder et al. 2019, 2021); central Pacific ( Cooke 1977, as Halopteris diaphana ); possibly Indian Ocean ( Jarvis 1922, as Plumularia alternata ; Gravely 1927, as Plumularia sp. nr. alternata ).

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.