Aglaophenia suensonii Jäderholm, 1896

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 : 47-48

Aglaophenia suensonii Jäderholm, 1896

Fig. 14b, c

Aglaophenia suensonii Jäderholm, 1896: 18 , pl. 2 fig. 9.

Type locality. Japan: Hirudostrasse (=Hirado Strait), 33°10ʹN, 129°16ʹE ( Jäderholm 1896) .

Voucher material. Laysan Island, detached, 17.ix.2002, three unbranched, monosiphonic cormoids, to 2.4 cm high, one with a corbula, coll. A. Faucci, ROMIZ B5463.

Remarks. Trophosomes of these hydroids conform most closely with accounts of Aglaophenia suensonii Jäderholm, 1896 by authors including Jäderholm (1896), Stechow (1909, 1913b, 1923c), Rho (1967), Hirohito (1995), and Xu et al. (2014b). Corbulae resemble those in type material of the species in being moderately long, with about 11 pairs of fused corbulacostae. Jäderholm did not include an illustration of the corbula in describing A. suensonii , but one was provided later by Stechow (1909: 91, fig. 6) based on an examination of the type. It was elongate, with about 16 pairs of fused corbulacostae that lacked basal hydrothecae. Some subsequent illustrations of corbulae attributed to the species have been shorter, with about 5–8 pairs of ribs (Stechow 1913; Rho 1967; Hirohito 1995).

Aglaophenia suensonii somewhat resembles the temperate to boreal A. pluma ( Linnaeus, 1758) of Europe and possibly elsewhere ( Svoboda & Cornelius 1991; Cornelius 1995b). It is distinguished by corbulae that reach to a greater length ( Stechow, 1923c), and by the shape of the marginal cusps of the hydrothecae. Unlike in A. pluma , the median abaxial hydrothecal cusp in A. suensonii is turned sharply inwards and is partly hidden in lateral view by a pair of large, arrowhead-shaped lateral cusps flanking it. In this, it approaches A. parvula Bale, 1881 , but differs in having nine rather than 10 marginal cusps. Moreover, the four pairs of lateral cusps are regularly wavy in shape and are mostly similar in size, rather than being irregular in both shape and size as in A. parvula . As for A. pluma , it has been considered a species complex based on 16S rRNA sequences by Moura et al. (2012, 2018, 2019).

Aglaophenia suensonii is a little-known species, reported elsewhere from warm waters of the western Pacific. The specific name has been spelled suensoni in some works, but suensonii is the original and correct spelling (ICZN 1999, Art. 32.2).

Reported Distribution. Hawaiian archipelago. First record.

Elsewhere. Southern Japan ( Hirohito 1995); southern South Korea ( Park 1995); East China Sea (Xu et al. 2014).

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.