Macrorhynchia phoenicea ( Busk, 1852 )

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 : 53-55

Macrorhynchia phoenicea ( Busk, 1852)

Fig. 14h, i

Plumularia phoenicea Busk, 1852: 398 .

Lytocarpus phoeniceus .— Nutting, 1905: 954.

Macrorhynchia phoenicea .— Di Camillo et al., 2009: 218, figs 2H–I, 6, 9.

Type locality. Australia: Torres Strait , Prince of Wales Channel ( Busk 1852) .

Voucher material. Gardner Pinnacles , 14.ix.2002, three colonies or colony fragments, to 4.4 cm high, with developing phylactogonia but no gonothecae, coll. A. Faucci, ROMIZ B5471 .— Midway Atoll, 23.ix.2002, two colonies, to 2.5 cm high, without gonophores, coll. A. Faucci, ROMIZ B5472 .— Midway Atoll, 20.ix.2002, one colony, 1.5 cm high, without gonophores, coll. A. Faucci, ROMIZ B5473 .— Midway Atoll, unattached, 20.ix.2002, three colonies or colony fragments, to 1.2 cm high, without gonophores, coll. A. Faucci, ROMIZ B5474 .— Gardner Pinnacles , 14.ix.2002, three colonies or colony fragments, to 4.3 cm high, without gonophores, coll. A. Faucci, ROMIZ B5475 .

Remarks. The species name Plumularia phoenicea was made nomenclaturally available through a brief, unillustrated account by British naturalist George Busk (1852). Bale (1884) provided the first detailed description and illustrations of it, under the binomen Aglaophenia phoenicea , based in part on material provided by Busk.

In an examination of Busk’s specimens at the British Museum, Billard (1909a) concluded that Plumularia aurita Busk, 1852 was conspecific with L. phoeniceus . Acting as First Reviser (ICZN 1999, Art. 24.2.2), he united the simultaneous synonyms under the binomen L. phoeniceus . Precedence was assigned to the specific name phoeniceus because it had taken on current usage while auritus had not subsequently been reported. If the demoted name was to be recognized as a variety, Billard (1910) proposed L. phoeniceus auritus for it, but that trinomen has not gained acceptance. Also assigned to the synonymy of M. phoenicea by Schuchert (2003) were Aglaophenia rostrata Kirchenpauer, 1872 , Lytocarpus spectabilis Allman, 1883 , and with question A. disjuncta Pictet, 1893 . Di Camillo et al. (2009) regarded A. rostrata , Lytocarpus sibogae Billard, 1913 and, with question, A. disjuncta as synonyms or questionable synonyms of the species. Lytocarpus spectabilis (= Macrorhynchia spectabilis ) was recognized by Di Camillo et al. as distinct, although its validity has been questioned by Postaire et al. (2016b) and Moura et al. (2018) based on molecular data. Meanwhile, the proposed synonymy of L. sibogae and M. phoenicea has been supported by results from 16S rRNA sequences by Postaire et al. As for A. disjuncta [= Macrorhynchia disjuncta ], Galea (2020) found that it differed morphologically in several respects from M. phoenicea . Colonies were said to be more delicate, cladia were comparatively longer and more separated, cormidia were longer, and hydrothecae were slightly larger. He therefore recognized M. disjuncta as valid and provided a redescription of it.

Hydroids assigned to M. phoenicea have long been characterized as decidedly varied in morphology (e.g., Bale 1884, as Aglaophenia phoenicea ; Marktanner-Turneretscher 1890, as Lytocarpus phoeniceus ; Billard 1910, 1913, as L. phoeniceus ; Stechow 1913b, as L. phoeniceus ; Jarvis 1922, as L. phoeniceus ; Vervoort 1946, as L. phoeniceus ; Ryland & Gibbons 1991; Schuchert 2003; Di Camillo et al. 2009). Evidence from several molecular studies now indicate the existence of crypsis within the morphological concept of the species (e.g., Postaire et al. (2016 a, b, 2017; Moura et al. 2018). From studies in the southwestern Indian Ocean, Postaire et al. (2016a) detected at least two biological species under M. phoenicea . These were distinguished morphologically, in terms of grey nomenclature ( Minelli 2017), as “morpho types ” A and B, and subsequently referred in Postaire et al. (2017) to M. phoenicea α and β. Hydroids of M. phoenicea α were typically tall (to 10 cm high), stiff, black and white in colour, and inhabit-ants of well-lighted locations swept by strong water currents. Those of M. phoenicea β were more gracile, usually brownish-orange in colour, and found under sheltered cliff edges. Their geographic distributions also differed ( Postaire et al. 2017), with M. phoenicea α occurring the western Indian Ocean and the Tropical Southwestern Pacific (as two lineages) and M. phoenicea β inhabiting the western Indian Ocean.

Such cryptic diversity was deemed by Postaire et al. (2016a) to be widespread in aglaopheniids. They attributed it largely to reduced gene flow due to a low capacity for dispersal ( Postaire et al. 2017). In M. phoenicea , for example, reproduction was reported to occur asexually by stolonization and sexually by brooded, short-lived larvae, thereby limiting propagule transport to short distances. Nevertheless, occasional dispersal of these hydroids by rafting and shipping is likely to occur.

Hydroids of M. phoenicea sensu lato are pinnate, often conspicuous, and of varied size, occasionally becoming quite large. Millard (1975) noted that magnificent flabelliform colonies up to 200 mm in height had been reported, likely based on the account of Billard (1913). Meanwhile, Kirkendale & Calder (2003) reported hydroids of the species from Guam that reached about 30 cm high. The synonymy lists of Vervoort & Watson (2003), Di Camillo et al. (2009), and Chakraborty & Raghunathan (2020) indicate how frequently hydroids of the morphospecies have been reported across the tropical Indo-Pacific. In Hawaii, Nutting (1905) described it as one of the most common hydroids in R/V Albatross collections from the islands. Specimens from waters off Kauai (USNM 22214) and Maui (USNM 22194) in that collection were re-examined and discussed by Di Camillo et al. (2009).

As with M. philippina Kirchanpauer, 1872 , this species has been reported as venomous to humans ( Santhanam 2020).

Reported Distribution. Hawaiian archipelago. Oahu: S coast, 229 m ( Nutting 1905, as Lytocarpus phoeniceus ); off Diamond Head, 519 m ( Nutting 1905, as Lytocarpus phoeniceus ).—Molokai: S coast, 110–134 m ( Nutting 1905, as L. phoeniceus ).—Laysan Island: to the N, 298 m ( Nutting 1905, as L. phoeniceus ).—Bird Island (=Nihoa): to the S, 59–708 m ( Nutting 1905, as L. phoeniceus ).—Kauai: to the N, 101 m ( Nutting 1905, as L. phoeniceus ; Di Camillo et al. 2009).—Maui: to the N, 95–102 m ( Nutting 1905, as L. phoeniceus ; Di Camillo et al. 2009).

Elsewhere. Tropical Indo-Pacific, from coral reef depths to 708 m ( Nutting 1905; Vervoort & Watson 2003), with a reported range from Natal, South Africa ( Millard 1975) in the southwestern Indian Ocean to the central Pacific ( Nutting 1905; Ryland & Gibbons 1991; Di Camillo et al. 2009).

Figures

FIGURE 14. Aglaopheniidae. a, Aglaophenia postdentata Billard, 1913, part of a cladium with two hydrothecae, Gardner Pinnacles, ROMIZ B5462. Scale equals 0.1 mm. b, Aglaophenia suensonii Jäderholm, 1896, part of a cladium with three hydrothecae, Laysan Island, ROMIZ B5463. Scale equals 0.1 mm. c, Aglaophenia suensonii Jäderholm, 1896, corbula, Laysan Island, ROMIZ B5463. Scale equals 0.2 mm. d, Aglaophenia whiteleggei Bale, 1888, part of a cladium with two hydrothecae, Pearl & HermesAtoll, ROMIZ B5464. Scale equals 0.1 mm. e, Lytocarpia flexuosa (Lamouroux, 1816), part of a cladium with three hydrothecae, Pearl & Hermes Atoll, ROMIZ B5479. Scale equals 0.1 mm. f, Lytocarpia phyteuma (Stechow, 1919b), part of a cladium with two hydrothecae, Pearl & Hermes Atoll, ROMIZ B5468. Scale equals 0.1 mm. g, Macrorhynchia philippina Kirchenpauer, 1872, part of a cladium with two hydrothecae, Midway Atoll, ROMIZ B5470. Scale equals 0.1 mm. h, Macrorhynchia phoenicea (Busk, 1852), part of a cladium with three hydrothecae, Gardner Pinnacles, ROMIZ B5475. Scale equals 0.1 mm. i, Macrorhynchia phoenicea (Busk, 1852), one phylactocarp, without gonothecae, Gardner Pinnacles, ROMIZ B5475. Scale equals 0.2 mm.