Aglaophenia postdentata Billard, 1913

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 : 46-47

Aglaophenia postdentata Billard, 1913

Fig. 14a

Aglaophenia postdentata Billard, 1913: 100 , fig. 89A–C. Type locality. Indonesia: Makassar and vicinity; Baie de Wunoh, NW de l’Île Waigeu (=Wunoh Bay, NW of Waigeo Island) ( Billard 1913).

Voucher material. Gardner Pinnacles, on Halimeda sp. , 14.ix.2002, one colony, 2.6 mm high, without corbulae, coll. A. Faucci, ROMIZ B5462 .— Gardner Pinnacles, on Halimeda sp. , 14.ix.2002, one colony, 2.0 mm high, without corbulae, coll. A. Faucci, ROMIZ B5487 .

Remarks. The hydroid of Aglaophenia postdentata Billard, 1913 is delicate, diminutive, and inconspicuous, with the single sterile colony observed here reaching a height of only 2.6 mm. Colonies of the species are commonly reported to be 5.0– 8.5 mm high ( Billard 1913; Jäderholm 1920; Vervoort 1941; Redier 1966; Millard & Bouillon 1973; Ryland & Gibbons 1991; Watson 2005; Moura 2020), although they are said to attain a height of about 1 cm ( Watson 1994b; Galea 2010).

Morphological accounts of this species include those of Billard (1913), Jäderholm (1920), Vervoort (1941), Redier (1966), Millard & Bouillon (1973), Ryland & Gibbons (1991), Watson (1994b, 2005), Galea (2010), and Moura (2020). The open corbula of the species has been described by Millard & Bouillon (1973), Watson (1994b), and Moura (2020). Hydroid specimens examined by Watson (1994b) were yellow in life, with pink gonophores.

The hydrotheca of A. postdentata is small, with its distalmost adaxial quarter free from the internode. An intrathecal ridge extends from the adaxial to the abaxial wall, and the ridge continues partway into the adjoining internode in the examined specimen. Ten quite sharp cusps occur on the rim, comprising single abaxial and adaxial cusps together with four laterals on each side. The adaxial cusp is prominent, unlike the shallow, broad equivalent sometimes seen in the similar A. pluma var. sibogae Billard, 1913 ( Schuchert 2003) .

The center of distribution of this infrequently reported little species appears to be the tropical Indo-west Pacific region. However, it is now known to be widely distributed ( Moura et al. 2018, 2019). In addition to its discovery in the central Pacific Ocean (this study), it has recently been reported from various locations in the Caribbean Sea ( Galea 2010; Moura et al. 2018, 2019), the Gulf of Guinea in the eastern Atlantic Ocean ( Moura et al. 2018), and from Brazil ( Moura 2020). Of note, the molecular phylogenies of Moura et al. indicate that populations of the species across its range are genetically quite close. However, such studies also reveal that A. postdentata is distant from Sertularia pluma Linnaeus, 1758 (= Aglaophenia pluma ), the type species of Aglaophenia Lamouroux, 1812 . Based on evidence from molecular phylogenetic studies, its inclusion in the genus has been justifiably questioned by Postaire et al. (2016b).

The reported depth distribution of the species is from 3 m ( Moura et al. 2018) to 102 m ( Moura 2020). In studies undertaken at Juan de Nova Island, Gravier-Bonnet & Bourmaud (2006) found it to be a species of the reef platform (<20 m).

Reported Distribution. Hawaiian archipelago. First record.

Elsewhere. Indo-west Pacific ( Billard 1913; Jäderholm 1920; Vervoort 1941; Redier 1966; Millard & Bouillon 1973; Ryland & Gibbons 1991; Watson 1994b, 1996, 2005; Gravier-Bonnet & Bourmaud 2006, 2012; Moura et al. 2018); western Atlantic ( Galea 2010; Moura et al. 2018; Moura 2020); eastern Atlantic ( Moura et al. 2018).

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.