Corallium regale Bayer 1956: 77–78, figs 5c, 7e-g; Nonaka and Muzik 2010: 106–107, figs 41–42; Tu et al. 2012: 5 (in key), fig. 13; Nonaka and Muzik 2012: 79 (in key), table 1.

Hemicorallium regale Tu et al. 2015b: 181 (in list), table 1; Tu et al. 2016: 1035 (in key), table II; Nonaka and Muzik 2016: 16 (in list).

Material examined. NSMT-Co 1733, Colahan Seamount, 605–682 m, 24 June 2011.

Diagnosis. Colony is branching almost in one plane. Contracted autozooids form cylindrical mounds, distributed unevenly on only one side of the colony, about 1.2 mm in diameter. Siphonozooids are distributed around the autozooids. Coenenchyme is thin, with a smooth surface, pale pink in color. Axis is stout with a smooth surface, pale red to pink in color. The burrows of commensal polychaetes are present on the surface of the axis. Tentacles contain shorter (0.075 mm long) thorny rods. Coenenchyme contains spherical 6- radiates, and 8-radiates, no double-clubs. Distributed in depths of about 600 m.

Description of specimen NSMT-Co 1733. Colony form. The specimen consists of 4 branchlets, about 30–60 mm long (Fig. 32A). The branching is almost in one plane, but whole colony form not determined (Fig. 32A). Branchlets are about 3 mm in diameter, with rounded cross sections.

Polyps. The autozooids are not retracted into the coenenchyme, making cylindrical mounds. They tend to be distributed on one side of the colony (Fig. 32B, C), rather crowded (Fig. 32B). They are 1.24± 0.13 mm in diameter and about 1.36 mm in height (Table 2). Siphonozooids are distributed around the autozooids (Fig. 33), about 0.06 mm in diameter.

Axis. The surface of the axis is smooth (Fig. 32C). There are no rounded pits on the surface of the axis at the position of each autozooids. The burrows of commensal organisms are found on the surface of the axis (Fig. 32B).

Coenenchyme. Coenenchyme is too thin to be measured. The surface is smooth and small warts are not remarkable (Fig. 33).

Color. The dry coenenchyme is pale pink. The axes are pink to pale red in color (Fig. 32).

Sclerites. The tentacles contain mainly rods (69%; 0.075± 0.014 mm long, 0.027± 0.005 mm wide), symmetric 8-radiates (15%; 0.061± 0.008 mm long, 0.038± 0.005 mm width), and a few 6-radiates, 7-radiates, multi-radiates and others (Figs 34, 35; Table 6).

The autozooid mounds contain mainly symmetric 6-radiates (34%; 0.058± 0.005 mm long, 0.044± 0.004 mm wide), asymmetric 6-radiates (22%; 0.056± 0.005 mm long, 0.043± 0.004 mm wide), 7-radiates (20%; 0.062± 0.005 mm long, 0.044± 0.002 mm wide). A few 8-radiates and multiradiates are present (Figs 34, 35; Table 6).

The branch tips contain mainly asymmetric 8-radiates (31%; 0.056± 0.005 mm long, 0.038± 0.003 mm wide), symmetric 8-radiates (27%; 0.061± 0.013 mm long, 0.038± 0.006 mm wide), 7-radiates (15%; 0.056± 0.009 mm long, 0.039± 0.004 mm wide), and a few 6-radiates, and multi-radiates (Figs 34, 35; Table 6).

Basal coenenchyme contains mainly symmetric 8-radiates (32%; 0.065± 0.012 mm long, 0.040± 0.005 mm wide) and asymmetric 8-radiates (21%; 0.061± 0.012 mm long, 0.042± 0.006 mm wide). There are a few crosses, 6-radiates, 7-radiates and multi-radiates (Figs 34, 35; Table 6) in the coenenchyme.

Remarks. Hemicorallium regale was first described in 1956 based on a specimen collected around French Frigate Shoals (697–711 m deep) in Hawaii in 1902 (Bayer 1956). This species resembles C. sulcatum and C. imperiale, but can be distinguished by presence of the unique spherically shaped 6-radiates in the coenenchyme. Such sclerites have been found in C. maderense and C. tricolor, but these two species are distributed in the Atlantic, not the Pacific. This species is the reddest in color of the precious corals from Hawaii, but was not collected in quantities large enough to prove commercially valuable.

The following features of specimen NSMT-Co 1733 fit the original description.

· The coenenchyme is thin, without fine protrusions.

· The axis is reddish or pink, with burrows of commensal organisms.

· The contracted autozooids are cylindrically shaped, 1.36 mm in height and 1.24 mm in diameter, and are unevenly distributed on one side of the colony.

· The dominant sclerites are 6-radiates and 8-radiates, and some 6-radiates have a spherical shape (Fig. 34). The rodshaped sclerites in the tentacles are thorny and relative short (0.075 mm long).

However, the height of the autozooids, and the length of the rod sclerites are shorter than those described for H. regale in Bayer 1956. H. regale was probably pinnately branched, but branching pattern cannot be determined from the present specimen. Therefore, this specimen is only tentatively identified as H. cf. regale in this study. For accurate identification, comparison with the holotype specimen will be required.