Iridogorgia squarrosa Xu, Zhan, Li & Xu, 2020

Figs. 13–16

Iridogorgia squarrosa Xu, Zhan, Li & Xu, 2020: 254–256, Figs 4–6.

Material examined: MBM286449, station FX-Dive 226 (10°38.22′N, 140°04.08′E), a seamount (tentatively named as M8) located on the Caroline Ridge in the tropical northwest Pacific, depth 1971 m, 14 June 2019 . MBM286876, station FX-Dive 174 (17°29.45′N, 153°14.01′E), Kocebu Guyot of Magellan Seamounts in the northwest Pacific, depth 1311 m, 8 April 2018 . BPBM D2955, station HURL Dive P5-672, specimen MOL601-4 (21°18.972′N, 157°1.282′W), off Molokai Is., Hawaiian Island chain, depth 1661 m, 6 September 2006 .

Diagnosis (modified from Xu et al. 2020): Colony with loosely coiled helices. Polyp cylindrical with a slightly expanded body base. Rods in tentacles covered with many small warts. Needles and rods at the base of tentacles flattened and often with sparse fine warts. Needles and elongated scales in the basal part of polyp body wall thick and of various shapes, often with sparse fine warts, some with large sculpture on surface. Needles in coenenchyme slender and nearly smooth with two sharp ends. Polyps and branches with verrucae.

Description: The three specimens match well with the description of I. squarrosa; herein the morphology of specimen MBM286449 is described in more detail. Colony grows on a rocky bottom with a small holdfast in situ (Fig. 13A). Specimen MBM286449 about 75 cm long with holdfast white about 2.5 mm in diameter (Fig. 13C). The direction of growth counterclockwise. Axis about 5 mm in diameter at base with dark iridescent metallic luster, including four helical turns with each turn 12–15 cm long and 1–2 cm in diameter. Branches arranged along one side of the axis, about 3 mm apart, and up to 17 cm long with 21 polyps counted. Polyps erect or slightly inclined along the branches, having a little contraction between the upper part and the slight expanded body base. Polyps cylindrical, 1–3 mm in height, 2–3 mm in width at base, and 4–8 mm apart (Fig. 13B, D–G). Polyps white after fixation in alcohol. Tentacular part 1.0– 1.5 mm long, 1–2 mm wide. Polyps and branches with a few verrucae.

Rods in the back of tentacle rachis longitudinally arranged, slender with many small warts and two rounded ends, usually forming eight distinct columns extending from tentacles to bases, and measuring 209–465 × 19–42 μm (Fig. 14A). Needles and rods at the base of tentacles longitudinally arranged, flattened and slender, often with sparse fine warts, occasionally nearly smooth, and measuring 317–555 × 35–76 μm (Fig. 14B). Needles and elongated scales in the basal part of polyp body wall transversely or obliquely arranged, usually thick with various shape and sparse small warts, some of them nearly smooth and with large irregular sculpture on surface, and measuring 70–665 × 21–100 μm (Fig. 14C). Needles in coenenchyme arranged along to the branch, slender and nearly smooth with two sharp ends, occasionally with fine warts, and measuring 126–1014 × 17–85 μm (Figs. 13H, 14D).

Distribution: A seamount near the Mariana Trench, 1458 m; off Molokai, Hawaii, 1661 m (Xu et al. 2020); Kocebu Guyot in Magellan Seamounts, 1311 m; a seamount located on the Caroline Ridge, 1971 m.

Remarks: Compared with the holotype and specimen MBM286876 (Fig. 15), specimens MBM286449 and MOL601-4 have none sclerites with the surface sculptured by something superficially similar to the ‘styles’ of sponges. Their mtMutS and 28S gene sequences showed they are identical with the intraspecific differences (see the genetic analysis above). Therefore, this morphological difference is not constant characters and can be treated as the intraspecific variation.