Hemicorallium sulcatum

Hemicorallium cf. sulcatum (Kishinouye, 1903a) (Figs 36–42; Tables 2, 6)

Corallium sulcatum Kishinouye, 1903a: 104; Kishinouye 1903b: 624; Kishinouye 1904: 24–25, pl. 4, figs 1, 2, pl. 7, fig. 3 (in Japanese); Kishinouye 1905: 23–24, pl. 4, figs 1, 2, pl. 7, fig. 3; Kukenthal 1924: 52; Bayer 1956: 75 (in key); Imahara 1996: 28 (in list); Nonaka and Muzik 2010: 96–97, figs 20–22; Tu et al. 2012: 5 (in key); 14–16, fig. 14; Nonaka et al. 2012: 5 (in key); Nonaka and Muzik 2012: 80 (in key), table 1.

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

Hemicorallium cf. sulcatum: Nonaka and Muzik 2016: 17– 24, figs 2–8, tables 1, 2.

Material examined. NSMT-Co 1734, Koko Seamount, 521–569 m, 20 August 2009. NSMT-Co 1735, Koko Seamount, 477–480 m, 9 August 2012. Diagnosis. Colony is branching in almost one plane,

terminal twigs tend to be bushy with some anastomoses. Contracted autozooids making cylindrical mounds, distributed one side of the colony, about 1.25 mm in diameter. On the tip of branch, 2–3 autozooids form clusters. Siphonozooids are inconspicuous. Coenenchyme is thin, smooth, with inconspicuous warts, pale pink in color. Axis is stout with inconspicuous longitudinal grooves, pale pink in color. The burrows of commensal polychaetes are present on the surface of axis. Tentacles contain long (> 0.1 mm long) rods, coenenchyme contains 8-radiates mainly, irregular-shapes present, no double-clubs. Distributed in depths of about 500 m.

Description of specimen NSMT-Co 1734. Colony form. The specimen is an almost complete colony, about 5 cm wide and 8 cm tall (Fig. 36A, B). The branching is almost in one plane, but terminal twigs tend to be bushy with some anastomoses. The sharp branchlets are about 2–3 mm in diameter (Fig. 36A, B). The cross section of the twigs is rounded.

Polyps. The autozooids are not retracted into the coenenchyme, making cylindrical mounds (Fig. 36C). They tend to be distributed on one side of the colony (Fig. 36A, B). On branch tips, 2–3 autozooids form clusters (Fig. 36A). They are 1.25± 0.19 mm in diameter and about 1.04 mm in height (Table 2). Siphonozooids are inconspicuous (Fig. 36C), about 0.06 mm in diameter (Table 2).

Axis. The surface of the axis is inconspicuously longitudinally grooved in about 0.34 mm intervals (Table 2). There are no rounded pits on the surface of the axis at the position of each autozooid. There are burrows in the axis, some with commensal polychaetes (Fig. 37).

Coenenchyme. Coenenchyme is thin, its thickness not measurable. The surface is smooth, small warts inconspicuous on the stems, but somewhat prominent on the twigs (Fig. 37). At high magnifications, the gastrovascular system can be seen through the thin coenenchyme on the side of the colony without autozooids (Fig. 37).

Color. The dry coenenchyme and axis are both pale pink in color (Figs 36, 37).

Sclerites. The tentacles contain mainly rods (55%; 0.121± 0.018 mm long, 0.028± 0.005 mm wide), symmetric 8-radiates (18%; 0.072± 0.009 mm long, 0.045± 0.004 mm wide), multi-radiates (18%; 0.089± 0.014 mm long, 0.039± 0.004 mm wide) and a few 6-radiates, 7-radiates and asymmetric 8-radiates (Figs 38, 39; Table 6).

The autozooid mounds contain mainly symmetric 8-radiates (56%; 0.074± 0.011 mm long, 0.046± 0.004 mm wide), asymmetric 8-radiates (21%; 0.067± 0.007 mm long, 0.044± 0.005 mm wide), multi-radiates (17%; 0.089± 0.017 mm long, 0.051± 0.006 mm wide). A few 6-radiates and 7-radiates are present (Figs 38, 39; Table 6).

The branch tips contain mainly asymmetric 8-radiates (48%; 0.064± 0.005 mm long, 0.045± 0.004 mm wide), symmetric 8-radiates (29%; 0.070± 0.011 mm long, 0.045± 0.004 mm wide), and a few 6-radiates, 7-radiates, multi-radiates (Figs 38, 39; Table 6).

The coenenchyme at the base contains mainly symmetric 8-radiates (41%; 0.061± 0.006 mm long, 0.041± 0.004 mm wide), asymmetric 8-radiates (29%; 0.060± 0.004 mm long, 0.042± 0.003 mm wide) and asymmetric 6-radiates (12%; 0.054± 0.005 mm long, 0.042± 0.005 mm wide). There are a few 7-radiates, multi-radiates and others (Figs 38, 39; Table 6) in the coenenchyme.

Description of specimen NSMT-Co 1735. Colony form. Since the specimen is only a small branchlet about 2 cm long (Fig. 40A), colony shape is unknown.

Polyps. The autozooids are not retracted into the coenenchyme, making cylindrical mounds. 2–3 autozooids form clusters on branch terminals (Fig. 40B). Autozooids are 1.24± 0.15 mm in diameter and 1.09± 0.19 mm in height (Table 2). Siphonozooids are inconspicuous (Fig. 40B), about 0.06 mm in diameter.

Axis. There are no rounded pits on the surface of the axis at the position of each autozooid.

Coenenchyme. Coenenchyme is so thin its thickness is not measurable. Small warts are present but inconspicuous, about 0.19 mm in diameter (Fig. 40B; Table 2). At high magnifications, the gastrovascular system can be seen (Fig. 40B).

Color. The dry coenenchyme is pale pink, axis is reddish. (Figs 40).

Sclerites. The tentacles contain mainly rods (53%; 0.104± 0.020 mm long, 0.027± 0.005 mm wide), symmetric 8-radiates (14%; 0.065± 0.009 mm long, 0.037± 0.005 mm wide), multi-radiates (33%; 0.081± 0.015 mm long, 0.037± 0.006 mm wide) (Figs 41, 42; Table 6).

The autozooid mounds contain mainly symmetric 8-radiates (48%; 0.069± 0.010 mm long, 0.043± 0.006 mm wide), asymmetric 8-radiates (18%; 0.068± 0.006 mm long, 0.044± 0.003 mm wide), and multi-radiates (21%; 0.082± 0.014 mm long, 0.045± 0.005 mm wide). A few 6-radiates and 7-radiates are present (Figs 41, 42; Table 6).

The branch tip contains mainly symmetric 8-radiates (62%; 0.064± 0.009 mm long, 0.040± 0.005 mm wide), asymmetric 8-radiates (21%; 0.066± 0.009 mm long, 0.043± 0.004 mm wide), and a few 6-radiates, 7-radiates, multi-radiates and others (Figs 41, 42; Table 6).

Coenenchyme on the base of the colony contains mainly symmetric 8-radiates (57%; 0.060± 0.006 mm long, 0.039± 0.004 mm wide) and asymmetric 8-radiates (23%; 0.058± 0.005 mm long, 0.040± 0.004 mm wide). There are a few 6-radiates, 7-radiates, multi-radiates and others (Figs 41, 42; Table 6) in the coenenchyme.

Remarks. Hemicorallium sulcatum was first described by Kishinouye (1903a), and the type locality is in Chiba Prefecture, Japan (Kishinouye 1903a, b). The specimen described by Kishinouye (1903a, b) was 30 cm in height, 21 cm in width, about 2.1 cm in diameter at the colony base, and taken from around 180 to 550 m deep off Chiba Prefecture off the coast, although the accurate depth was not recorded (Kishinouye 1904). Kishinouye received only two specimens, one of which had already been halfway polished, so he reported he could not study it for taxonomic research (Kishinouye 1904). Both specimens are currently lost. Several specimens were subsequently identified as belonging to this species (Tu et al. 2012; Nonaka et al. 2016), but identifications cannot be confirmed without comparison with the still-missing type-specimen.

In specimen NSMT-Co 1734 the features recorded below fit the original description of this species:

· The colony is branched in one plane, and has some anastomoses.

· The autozooids are unevenly distributed on one side of the colony.

· Some perforated grooves can be found on the axis. The axis is pale pink in color.

· The sclerites are predominantly 8 radiates, and some irregular shaped can also be found.

In specimen NSMT-Co 1735, consisting of only a branch tip, sclerite features mostly fit the original description.

Regarding autozooid size, there was no record in the original description (Kishinouye 1903a, b). The papers published subsequently by Kishinouye in 1904 had more detailed descriptions of this species, but the length units he used to report autozooid size differed in the Japanese and the English versions. In the Japanese version (Kishinouye 1904), the height was 3–6 “rin” (0.9–1.8 mm) and the diameter was 3 “rin” (0.9 mm), whereas in the English version (Kishinouye 1905), height was about 2 mm and diameter 1.5 mm. The specimens examined here have autozooids which are slightly shorter (1.0– 1.1 mm) than in the original description, but almost the same diameter (1.25 mm).

Although these specimens best resemble H. sulcatum, some morphological characters do not fit, therefore, they are only tentatively identified as H. cf. sulcatum in this study. For precise identification, it will be necessary to designate a neotype in the future.