Hemicorallium meraboshi, Nonaka & Hanahara & Kakui, 2023

Nonaka, Masanori, Hanahara, Nozomi & Kakui, Keiichi, 2023, A New Species of Coralliidae (Cnidaria: Octocorallia) Collected from Eastern Japan, Species Diversity 28 (2), pp. 231-243 : 232-237

publication ID	https://doi.org/ 10.12782/specdiv.28.231
publication LSID	lsid:zoobank.org:pub:01B87E02-9319-40F1-B2E7-D36F4F1FC2FC
persistent identifier	https://treatment.plazi.org/id/EA27A284-716A-49C4-9C61-CE9B71EF2E7C
taxon LSID	lsid:zoobank.org:act:EA27A284-716A-49C4-9C61-CE9B71EF2E7C
treatment provided by	Felipe
scientific name	Hemicorallium meraboshi
status	sp. nov.

Treatment

Hemicorallium meraboshi sp. nov.

[Japanese common name: Meraboshi-sango] ( Figs 3–18 View Fig ; Tables 1, 2)

Material examined. Holotype, NSMT-Co 1801; 36°51.8′N 144°48.8′E to 36°51.5′N 144°48.7′E, Stn. Kago-7, Iwaki Seamount , Northwestern Pacific, 1744–1755 m depth, 9 August 2009, coll. by Keiichi Kakui. GoogleMaps

Diagnosis. Branched colony in almost one plane without anastomoses. Branching irregular, at close to right angles near the base and acute angles in twigs. Contracted autozooids sparsely distributed on stem of one side of the colony, at approximately 5–10 mm intervals on twigs. Two to three autozooids form clusters on branch tips. Autozooid diameter 1.7–2.8 mm (average 2.24 mm) and height 1.0– 2.3 mm (average 1.66 mm): bright red in color. Coenenchyme 0.10–0.19 mm (average 0.14 mm) thick, pale pink in color, with inconspicuous longitudinal grooves. Axis stout, no pits underneath autozooids, surface smooth, white in color. Tentacles contain blunt warty rods, elongate multi-radiate mainly, coenenchyme contains 8-radiates and multi-radiates. Double clubs absent.

Description of the holotype. Colony form. The specimen comprised nine parts of a colony. The largest two parts are shown in Fig. 3 View Fig , larger one is approximately 85 mm tall and 70 mm wide, and is branched almost in one plane without anastomoses ( Fig. 3 View Fig ). Their angle of branching is almost right in the stem but acute in twigs. At some bifurcation of the acute-angled twigs, there is a part where the crotch of the two twigs adheres to form a thin membrane ( Figs 3 View Fig , 5 View Fig , 10). Thick stem diameter greater than 10 mm, and thinnest branch tip is approximately 2–3 mm. Branch cross-sections are almost rounded to oval ( Fig. 14 View Fig ).

Polyps. Autozooids are not retracted into coenenchyme, forming cylindrical mounds with 8 longitudinal striations ( Figs 4–7) distributed mainly on one side of colony ( Figs 3 View Fig , 5 View Fig , 10). They are sparsely distributed on the stem at approximately 5–10 mm intervals ( Fig. 3 View Fig ), with 2–3 autozooids clustered on branch tips ( Figs 4–6). Diameter of autozooid mound is 2.24 ± 0.28 mm (N = 43); height 1.66 ± 0.35 mm (N = 10). Inconspicuous siphonozooids are distributed around autozooids, 0.10 ± 0.018 mm in diameter (N = 10) ( Figs 7–9 View Fig View Fig View Fig ).

Axis. Axis surface is smooth, weakly striated ( Figs 12, 13). No rounded pits are observed on axis surface at each autozooid position. A few commensal burrows are present along axis ( Fig. 11 View Fig ).

Coenenchyme. Coenenchyme is thin, 0.14 ± 0.034 mm (N = 10) ( Fig. 14 View Fig ), smooth, with weak longitudinal grooves (in approximately 0.39 mm intervals) on colony surface ( Figs 9 View Fig , 10).

Color. Fresh coenenchyme is pale pink on branch: bright red on autozooid mounds ( Fig. 3 View Fig ). Preserved specimen is faded and discolored whitish. Axis is white in color ( Figs 12–14).

Sclerites. Tentacles have mainly rods (37%; 0.142 ± 0.019 mm long, 0.041 ± 0.008 mm wide), elongated multi-radiates (34%; 0.117 ± 0.019 mm long, 0.054 ± 0.005 mm wide), spherical multi-radiates (20%; 0.093 ± 0.008 mm long, 0.057 ± 0.006 mm wide), a few 8-radiates, and others ( Figs 15 View Fig , 17; Table 1).

Autozooid mounds contain mainly elongated multi-radiates (50%; 0.104 ± 0.008 mm long, 0.056 ± 0.004 mm wide), spherical multi-radiates (25%; 0.093 ± 0.008 mm long, 0.057 ± 0.005 mm wide), symmetrical 8-radiates (12%; 0.094 ± 0.008 mm long, 0.051 ± 0.005 mm wide), and some 7-radiates, asymmetrical 8-radiates, crossed multi-radiates, and others ( Figs 15 View Fig , 17; Table 1).

Branch tips contain mainly symmetrical 8-radiates (55%; 0.081 ± 0.008 mm long, 0.049 ± 0.004 mm wide), asymmetrical 8-radiates (21%; 0.079 ± 0.006 mm long, 0.048 ± 0.004 mm wide), elongated multi-radiates (16%; 0.092 ± 0.015 mm long, 0.051 ± 0.006 mm wide), a few 6-radiates, 7-radiates, multi-radiates (spherical and cross), and others ( Figs 16 View Fig , 17; Table 1).

Coenenchyme on colony base contains mainly asymmetric 8-radiates (38%; 0.077 ± 0.004 mm long, 0.046 ± 0.003 mm wide), symmetric 8-radiates (33%; 0.076 ± 0.005 mm long, 0.046 ± 0.003 mm wide), and spherical multi-radiates (10%; 0.066 ± 0.005 mm long, 0.058 ± 0.004 mm wide). A few 6-radiates, 7-radiates, and multi-radiates (elongated and crossed) are present ( Figs 16 View Fig , 17; Table 1).

Etymology. The specific name “meraboshi ” is a Japanese noun that has been passed down from ancient times on the Pacific coast of Japan and refers to the Canopus of the Argo constellation. In this region, the Canopus is a rare star that can only be observed under certain seasonal and weath- er conditions. This red star has been revered as the god who controls maritime conditions, and if seen near the eastern horizon, it is said that the sea will be rough ( Nojiri 1957: 257–264). The described coral inhabits the eastern offshore region of this area, and has bright red autozooids, hence the specific name given of “meraboshi .”

Remarks. Tu et al. (2015) described the morphological characteristics of the genus Hemicorallium as follows: contracted autozooids that are not retracted in the coenenchyme, cylindrical in shape, and usually distributed on one side of the colony. The tentacles contain rod-shaped sclerites. All of these characteristics were found in the holotype of the new species.

Among the species of the genus Hemicorallium described from Hawaii and the western Pacific, H. meraboshi sp. nov. has the largest autozooid mounds (2.24 ± 0.28 mm in diameter) ( Table 3). Those of H. abyssale ( Bayer, 1956) , H. guttatum Tu, Dai, and Jeng, 2016 , H. laauense ( Bayer, 1956) , H. regale ( Bayer, 1956) and H. sulcatum are also large, i.e., larger that are more than 1.5 mm in diameter. However, they differ from the new species in the following morphological characters.

Hemicorallium abyssale has a pale pink axis and pink coenenchyme, no cluster of autozooid, and has double-club sclerites in the coenenchyme dominantly. Hemicorallium guttatum has yellowish white coenenchyme, very tall autozooid mounds (diameter <height), and spherical 8-radiates in the coenenchyme. Both coenenchyme and autozooid mounds of H. laauense are white in color. Those of H. regale and H. sulcatum are all pale pink.

The unique characteristics of H. meraboshi sp. nov. are that it has thin membranes between two twigs ( Figs 2 View Fig , 4, 9 View Fig ), and large (over 0.1 mm long) multi-radiate sclerites ( Figs 14 View Fig , 16 View Fig ) in the tentacles and autozooid mounds.

Molecular analysis. The phylogenetic tree retrieved with Bayesian inference ( Fig. 18 View Fig ) recovered well-supported topologies concordant with the clades ( Corallium clade, Hemicorallium clade, Pleurocorallium clade) hypothesized by Tu et al. (2015) and indicated that the new species was included in the Hemicorallium clade.