Iridogorgia squarrosa n. sp.

(Figs 4–6; Table 1)

urn:lsid:zoobank.org:act: 3F790F33-4282-4A8E-802C-70B8ED2A69D2

Holotype: MBM286539, collected on March 2016 from the station FX-Dive 70 (11°16.25’N, 139°25.51’E) of a seamount near the Mariana Trench with water depth of 1458 m. GenBank accession MK 431865.

Diagnosis: Colony with a brown to black axis. Polyp bodies with eight obvious columns extending from tentacles to bases. Surface of sclerites usually sculptured by numerous large tuberculate warts or something superficially similar to the ‘styles’ of sponges. Rods in tentacles and rod-like scales at base. Broad scales in polyp bodies with various shapes. Coenenchyme with numerous slender spindles.

Description: In vivo, colony large with six helical turns on the top and long central branches, approximately 30–40 cm long (Fig. 4A). The bottom of colony absent, and the remainder 84.5 cm long. Each complete turn 13–15 cm in height and 4–5 cm in diameter. Central axis 5 mm in diameter at base with dark brown luster, color gradually deepened to nearly black at the top. Branches arranged along one side of axis, originating every 3–4 mm. All branches broken, with the most complete one measured 15 cm long with 22 polyps (Fig. 4B). Polyps 2–6 mm apart, usually 2–4 mm high and 1–2 mm wide. Tentacles up to 3 mm long, forming eight obvious columns extending to polyp bases (Fig. 4C). Verrucae present in body walls and along branches.

Sclerites arranged longitudinally in tentacles and bodies, transversely in branches, dispersedly at the bases of polyps (Fig. 4D). Surface of sclerites usually sculptured by numerous large tuberculate warts or thickened ‘styles’ (in the sense of the spicule commonly seen in sponges, as described in Watling, 2007). Rods in tentacles rough, with dense and sharp protuberances, measuring 325–433 × 26–43 µm with an average of 382 × 37 µm (Fig. 5A). Rodlike scales in the back of tentacles elongated, sometimes with rugged surface and a few warts, measuring 467–805 × 48–66 µm with an average of 579 × 57 µm (Fig. 5B). Coenenchyme covered closely with long spindles, almost with one or two sharp ends, measuring 180–840 × 23–60 µm with an average of 502 × 45 µm (Fig. 4E, 5C). Lower portion of polyps connected to branches with abundant scales, of various shapes, most with a constriction midway along their length and sculptures similar to the ‘styles’ of sponges on the surface, measuring 72–569 × 24–150 µm with an average of 396 × 77 µm (Fig. 5D, 6).

Etymology: The Latin adjective squarrosus (squarrose) refers to the coarse sculptures in sclerites of the species.

Distribution: Known from the type locality, a seamount near the Mariana Trench with water depth of 1458 m. Growing on a rocky bottom with the temperature 3.1°C and the salinity 35.8. This species has also been found off Molokai, Hawaii (Dive Pisces V-672, depth 1661 m) (Watling, personal communication).