Iridogorgia fontinalis Watling, 2007

Iridogorgia fontinalis Watling, 2007 View in CoL

Figs. 17–22 View FIGURE 17 View FIGURE 18 View FIGURE 19 View FIGURE 20 View FIGURE 21 View FIGURE 22

Iridogorgia fontinalis Watling, 2007: 398–400 View in CoL , Figs 6 View FIGURE 6 , 7 View FIGURE 7 .

Material examined: MBM286362 View Materials , station FX-Dive 173 ( 17°28.28′N, 153°10.54′E), Kocebu Guyot of Magellan Seamounts in the northwest Pacific, depth 1303 m, 7 April 2018 GoogleMaps . MBM286363 View Materials , station FX-Dive 178 ( 17°20.40′N, 152°41.88′E), Kocebu Guyot , depth 1596 m, 12 April 2018 GoogleMaps . MBM286458 View Materials , station FX-Dive 211 ( 10°03.18′N, 140°10.60′E), a seamount (tentatively named as M5) located on the Caroline Ridge in the tropical northwest Pacific, depth 1393 m, 29 May 2019 GoogleMaps . MBM286459 View Materials , station FX-Dive 224 ( 10°37.63′N, 140°05.45′E), a seamount (tentatively named as M8) located on the Caroline Ridge , depth 1504 m, 12 June 2019 GoogleMaps . MBM286452 View Materials , station FXDive 211 ( 10°02.93′N, 140°10.48′E), a seamount (tentatively named as M5) located on the Caroline Ridge , depth 1482 m, 29 May 2019 GoogleMaps .

Diagnosis (modified from Watling 2007): Colony with closely coiled helices and branches at the top of the colony forming a beautiful fountain shape. Polyps cylindrical with a slight expanded body base. Rods in tentacles covered with many small warts. Needles and rods in the polyp body wall thick and nearly smooth, some of them flattened and broad. Needles in coenenchyme slender and nearly smooth. Polyps and branches with a few verrucae.

Description: The four specimens (MBM286362, 286363, 286458 and 286458) all match well with the previous description of I. fontinalis Watling, 2007 ; herein the morphology of specimen MBM286459 is described in more detail. Colony growing on a rocky bottom with a small white holdfast in situ ( Fig. 17B View FIGURE 17 ). Specimen about 78 cm long with the holdfast not recovered ( Fig. 17F View FIGURE 17 ). The direction of growth clockwise or counter-clockwise (clockwise in MBM286458, counter-clockwise in MBM286362 and MBM286363). Axis having 16 helical turns, uniformly coiled from the middle to top, about 4.5 mm in diameter at base with iridescent metallic luster. Each helical turn 4–6 cm long and 2–3 cm in diameter. The branching part about 15 cm in height including five helical turns. Branches arc-shaped forming a fountain spray shape, and arranged along one side of the axis, 1.0– 1.5 mm apart, and up to 20 cm long with 32 polyps counted. Polyps cylindrical, usually with a slight expanded body base, 1–3 mm in height, and 2–5 mm in width at base ( Fig. 18D, F, G View FIGURE 18 ). Polyps 2–6 mm apart at the distal part of branch, and became sparse and up to 20 mm at the proximal part ( Fig. 18C View FIGURE 18 ). Tentacular part 1–2 mm long, 1.0– 1.5 mm wide, usually forming eight obvious parallel columns terminating at its base. Polyps white after fixation. Polyps and branches with a few verrucae.

Compared with the four specimens, another specimen MBM286452 has some differences in morphology. It is about 130 cm in height with a long unbranched axis and the holdfast not recovered ( Fig. 19C View FIGURE 19 ). The direction of growth clockwise. Axis uniformly coiled from the bottom to top like a wire spring, having 26 helical turns, about 7 mm in diameter at base with light iridescent metallic luster. Each helical turn 4–6 cm long and 2–3 cm in diameter. Branching part about 20 cm in height with four helical turns. Branches 1.0– 1.5 mm apart, and up to 20 cm long with 29 polyps counted. Polyp claret-colored or a little pink after fixation, 1–4 mm in height average 3 mm, and 2–3 mm in width at base, 3–5 mm apart ( Fig. 19D–G View FIGURE 19 ). Tentacular part 1–2 mm long, 1 mm wide. Some polyps with a large expanded body base and golden eggs visible under the light microscope ( Fig. 19F View FIGURE 19 ). Verrucae rare to absent in polyps and branches.

The five specimens have similar sclerites. Their polyps and coenenchyme all covered with numerous sclerites ( Figs. 18F,G View FIGURE 18 ; 19H, I View FIGURE 19 ). Rods in the back of tentacle rachis longitudinally arranged, slender and regular with two round ends and many small warts, occasionally with a few large irregular warts and shallow cracks on surface, and measuring 168–553 × 26–65 μm ( Figs. 20A View FIGURE 20 , 21A View FIGURE 21 , 22A View FIGURE 22 ). Needles and rods in the polyp body wall transversely or longitudinally arranged, thick and nearly smooth, some of them flattened, occasionally branched with irregular shape and large warts, and measuring 129–1039 × 21–129 μm ( Fig. 20C View FIGURE 20 , 21B View FIGURE 21 , 22B View FIGURE 22 ). Needles in coenenchyme arranged along to the branch, slender and thick with nearly smooth surface, occasionally with sparse fine or large warts, and measuring 143–1212 × 21–118 μm ( Figs. 20B View FIGURE 20 , 21C View FIGURE 21 , 22C View FIGURE 22 ).

Distribution: Atlantic: Corner Rise seamounts, 1325 m ( Watling 2007); Pacific: Kocebu Guyot in Magellan seamounts, 1303–1596 m; seamounts located on the Caroline Ridge, 1393–1504 m. Additional specimens recorded in video from the Central Pacific. Two specimens (BPBM D2946 and D2947) collected on Twin Banks, Northwest Hawaiian Islands Ridge ( 23°8.152′N, 163°9.301′W), depth 1310 and 1384 m, attributed to this species, but not verified genetically.

Remarks: Our five specimens and the holotype of Iridogorgia fontinalis Watling, 2007 all have a fountain shape, similar helical height and diameter, branch interval, polyp size, and the same sclerite forms and arrangement. However, s pecimen MBM286452 differs from others by a longer unbranched axis with more helices, claret-colored or a little pink polyps after fixation. These differences are not constant characters and may be caused by different growth stage and environment, and can be treated as the intraspecific variation. Based on the morphological and phylogenetic analyses, the five specimens were all identified as the same species. Iridogorgia fontinalis is a newly recorded species in the Western Pacific.