Iridogorgia splendens Watling, 2007

Iridogorgia splendens Watling, 2007 View in CoL

Figs. 5–7 View FIGURE 5 View FIGURE 6 View FIGURE 7

Iridogorgia splendens Watling, 2007: 397–398 View in CoL , Figs 4 View FIGURE 4 , 5 View FIGURE 5 .

Material examined: MBM286457 View Materials , station FX-Dive 222 ( 10°07.95′N, 140°14.40′E), a seamount (temporarily named as M6) located on the Caroline Ridge in the tropical northwest Pacific, depth 1077 m, 6 June 2019 GoogleMaps .

Diagnosis (redefined on the basis of Watling 2007): Colony relatively short. Axis closely coiled with helical turn 4–5 cm long. Polyps with an expanded body base and abundant sclerites, including rods and needles with fine warts. Rods sparse and longitudinally arranged at the tentacle bases. Sclerites in coenenchyme between the polyps rare to absent.

Description: Specimen deep orange after collection, about 56 cm long with the holdfast rounded and white about 3 cm in diameter ( Fig. 5B View FIGURE 5 ). The direction of growth clockwise. Axis closely coiled spiraling upward and with iridescent metallic luster, about 6 mm in diameter at base. Branching part about 33 cm long, including seven helical turns with each turn 4–5 cm long and 1–2 cm in diameter. Branches slightly arc-shaped, up to 15 cm long, 2–3 mm apart, and arranged along one side of the axis, with 21 polyps counted.

Polyps with an expanded body base, 1.0– 1.5 mm in height, 1–3 mm in width at base, and 3–8 mm apart ( Fig. 5C–G View FIGURE 5 ). Tentacular part usually gathered and dome-shaped after fixation, about 1 mm long and 1.0– 1.5 mm wide. Proximal polyps small, sometimes with extended tentacles ( Fig. 5F, G View FIGURE 5 ). Polyps and branches with rare verrucae.

Sclerites thick and often with irregular outline and unevenly distributed small warts ( Fig. 6C View FIGURE 6 ), scales absent. Rods in the back of tentacle rachis sparse and longitudinally arranged at the base, some of them irregular and with shallow cracks on surface, occasionally crossed, and measuring 132–471 × 12–100 μm ( Figs. 5H View FIGURE 5 ; 6A View FIGURE 6 ). Needles and rods in the polyp body wall transversely arranged, some of them branched or crossed with irregular shape and rugged surface, occasionally with large warts, and measuring 130–1200 × 18–162 μm ( Figs. 5I View FIGURE 5 ; 6B View FIGURE 6 ). Needles in the coenenchyme arranged along to the branch, slender and usually with two pointed ends, and measuring 161–1246 × 16–123 μm ( Figs. 5J View FIGURE 5 , 6D View FIGURE 6 ).

Distribution: Rehoboth Seamount and Kelvin Seamount in the northwest Atlantic, 1844–2054 m ( Watling 2007); a seamount located on the Caroline Ridge in the western Pacific, 1077 m.

Remarks: This specimen matches well with the holotype in its short colony with relatively tightly coiled central axis, short polyps with expanded body base, sparse sclerites at the tentacle bases, sclerites rare to absent in the coenenchyme between the polyps. Moreover, their 28S gene sequences showed they are identical with the intraspecific differences (see the genetic analysis above). This specimen differs from the holotype and paratypes by more irregular sclerites in the polyp body wall and tentacles ( Figs. 6 View FIGURE 6 , 7 View FIGURE 7 ; Watling 2007). However, these differences may be caused by inadequate measurement and description of the holotype, which needs redescription.