taxonID	type	description	language	source
713F8790FFB0FFD695DDFD87812BF7BA.taxon	materials_examined	Material examined. Holotype: NSMT-Co 1914, around Okinawa Island, 860 m depth, 10 September 2013, collected by Takashi Ganaha.	en	Nonaka, Masanori, Takata, Kenji, Yasuda, Nina (2025): A New Species of the Genus Hemicorallium (Cnidaria: Octocorallia: Scleralcyonacea: Coralliidae) Collected from Okinawa Island. Species Diversity 30 (2): 193-206, DOI: 10.12782/specdiv.30.193, URL: https://doi.org/10.12782/specdiv.30.193
713F8790FFB0FFD695DDFD87812BF7BA.taxon	diagnosis	Diagnosis. Colony branched in one plane with some anastomoses; irregularly dichotomous branching, at acute or right angles near base and at acute angles in twigs. Contracted autozooids distributed three-dimensionally throughout colony, at 4 mm intervals on stem and 2.5 mm intervals on twigs on average. They tend to be arranged in two pairs at branch tips, without clusters. Autozooid diameter 1.1 – 2.0 mm (avg. 1.66 mm) and height 1.2 – 2.0 mm (avg. 1.53 mm). Coenenchyme 0.07 – 0.15 mm (avg. 0.11 mm) thick, pale pink, with inconspicuous warts. Stout axis, no pits beneath autozooids, and smooth and red surface. Tentacles contain blunt warty rods, mainly elongate multi-radiates; coenenchyme contains 8 - radiates and multi-radiates. Double clubs absent.	en	Nonaka, Masanori, Takata, Kenji, Yasuda, Nina (2025): A New Species of the Genus Hemicorallium (Cnidaria: Octocorallia: Scleralcyonacea: Coralliidae) Collected from Okinawa Island. Species Diversity 30 (2): 193-206, DOI: 10.12782/specdiv.30.193, URL: https://doi.org/10.12782/specdiv.30.193
713F8790FFB0FFD695DDFD87812BF7BA.taxon	description	Description of the holotype. Colony form. The specimen is an almost complete colony (Fig. 2), measuring approximately 125 mm in height and 100 mm in width. The branching is fan-shaped and irregularly dichotomous in one plane. The angles of branching are acute to right angle in the stem and acute in the twigs. The diameter of the thickest part of the stem is approximately 5 mm, whereas the thinnest branch tips measure 1 – 2 mm. The branches tend to gradually thin from the base to the tip. There are three instances of anastomosis on the branchlets (Fig. 3), although some pairs of branches may appear to be joined in photographs. The branch cross-sections are almost rounded (Fig. 4). Polyps. Autozooids are not retracted into the coenenchyme but form cylindrical mounds with eight longitudinal striations (Figs 5, 8 – 10), distributed three-dimensionally across the colony (on both sides and laterally). There are almost no autozooids on the opposite side of the colony (Figs 2, 7). They are sparsely distributed along the stem, at intervals of 4.08 ± 1.00 mm (N = 13) (Fig. 6), but are relatively crowded and regularly spaced on the branchlets, at intervals of 2.47 ± 0.39 mm (N = 15) (Figs 8, 9). The autozooids tend to be distributed in pairs on the branchlets, but without forming clusters (Figs 8, 9). The diameter of the autozooid mounds is 1.66 ± 0.18 mm (N = 60), and their height is 1.53 ± 0.18 mm (N = 19). Inconspicuous siphonozooids are distributed mainly on the opposite side and around the autozooids, with a diameter of 0.035 ± 0.008 mm (N = 13) (Figs 8, 9, 11). Axis. The axis is smooth without commensal burrows on the surface (Figs 10, 12 – 14). No rounded pits were observed at the autozooid positions. Coenenchyme. The coenenchyme is rather thin, measuring 0.11 ± 0.025 mm (N = 17) (Figs 4, 14). Small and inconspicuous warts, approximately 0.24 ± 0.03 mm in diameter (N = 26), are distributed on both sides, along with weak longitudinal grooves (Figs 4, 6, 11). At high magnification, the gastrovascular system was visible in the cross-section of the branch (Fig. 4) and through the thin coenenchyme (Fig. 13). Color. The preserved specimens were pale pink under wet conditions and cream yellow under dry conditions (Figs 2, 6 – 9, 11). The axis is red (Figs 4, 10, 12 – 14). Sclerites. The tentacles predominantly contain rods (49 %; 0.099 ± 0.011 mm long, 0.028 ± 0.006 mm wide; N = 74), elongated multi-radiates (42 %; 0.085 ± 0.010 mm long, 0.039 ± 0.005 mm wide; N = 63), with a few 8 - radiates and 6 - radiates (Figs 15, 17; Table 1). The autozooid mounds mainly consist of elongated multi-radiates (83 %; 0.089 ± 0.005 mm long, 0.046 ± 0.003 mm wide; N = 97). Some 6 -, 7 -, and 8 - radiates as well as other types, are present (Figs 15, 17; Table 1). The branch tips primarily contain asymmetrical 8 - radiates (46 %; 0.062 ± 0.005 mm long, 0.037 ± 0.003 mm wide; N = 42), elongated multi-radiates (41 %; 0.076 ± 0.010 mm long, 0.041 ± 0.004 mm wide; N = 37), with a few 6 -, 7 - radiates, symmetrical 8 - radiates, and other types (Figs 16, 17; Table 1). The coenenchyme on the colony base mainly contains symmetric 8 - radiates (41 %; 0.054 ± 0.007 mm long, 0.033 ± 0.004 mm wide; N = 33), asymmetric 8 - radiates (26 %; 0.056 ± 0.004 mm long, 0.034 ± 0.003 mm wide; N = 21), and multi-radiates (25 %; 0.059 ± 0.009 mm long, 0.035 ± 0.003 mm wide; N = 20). A few 6 - and 7 - radiates are also present (Figs 16, 17; Table 1).	en	Nonaka, Masanori, Takata, Kenji, Yasuda, Nina (2025): A New Species of the Genus Hemicorallium (Cnidaria: Octocorallia: Scleralcyonacea: Coralliidae) Collected from Okinawa Island. Species Diversity 30 (2): 193-206, DOI: 10.12782/specdiv.30.193, URL: https://doi.org/10.12782/specdiv.30.193
713F8790FFB0FFD695DDFD87812BF7BA.taxon	etymology	Etymology. The species is named after the region from which it was collected off Okinawa Island. The Ryukyu Archipelago, which includes Okinawa Island, was once the center of the prosperous Ryukyu Kingdom. Today, both “ Okinawa ” and “ Ryukyu ” are used to describe the area, but “ Ryukyu ” carries a more traditional resonance. In naming this new species, we have chosen to honor that tradition and selected “ Ryukyu ” for the specific name.	en	Nonaka, Masanori, Takata, Kenji, Yasuda, Nina (2025): A New Species of the Genus Hemicorallium (Cnidaria: Octocorallia: Scleralcyonacea: Coralliidae) Collected from Okinawa Island. Species Diversity 30 (2): 193-206, DOI: 10.12782/specdiv.30.193, URL: https://doi.org/10.12782/specdiv.30.193
713F8790FFB0FFD695DDFD87812BF7BA.taxon	discussion	Remarks. Tu et al. (2015) described the morphological characteristics of the genus Hemicorallium as follows: contracted autozooids that are not retracted into the coenenchyme, cylindrical in shape, and typically distributed on one side of the colony. The tentacles contain rod-shaped sclerites. All of these characteristics were found in the holotype of H. ryukyuense. Among the species of Hemicorallium described from Hawaii and the western Pacific, the holotype of this species has larger autozooid mounds (1.66 ± 0.18 mm in diameter, 1.53 ± 0.18 mm in height). The autozooid mounds of H. abyssale (Bayer, 1956), H. boshuense (Kishinouye, 1903), H. guttatum Tu, Dai, and Jeng, 2016, H. halmaheirense (Hickson, 1907), H. meraboshi Nonaka, Hanahara, and Kakui, 2023, H. regale (Bayer, 1956), H. reginae (Hickson, 1905), H. sulcatum, and H. variabile (Thomson and Henderson, 1906) are also large, measuring more than 1.5 mm in both diameter and height. Among these species, only three (H. abyssale, H. regale, and H. sulcatum) exhibit a pinkish or reddish cortex and axis.	en	Nonaka, Masanori, Takata, Kenji, Yasuda, Nina (2025): A New Species of the Genus Hemicorallium (Cnidaria: Octocorallia: Scleralcyonacea: Coralliidae) Collected from Okinawa Island. Species Diversity 30 (2): 193-206, DOI: 10.12782/specdiv.30.193, URL: https://doi.org/10.12782/specdiv.30.193
713F8790FFB0FFD695DDFD87812BF7BA.taxon	description	Nonaka and Muzik (2016) examined a specimen stored at the Smithsonian Institution, collected from 800 m deep near Tsuken Island, Okinawa Islands, and identified it as H. cf. sulcatum. This specimen (USNM 76105) was collected from a similar area and depth to the holotype of H. ryukyuense and appears morphologically similar. However, the autozooid mounds of this specimen are smaller (1.16 mm in diameter and 1.04 mm in height), and the composition and size of the sclerites differ, making it clear that it is not the same species. Molecular analysis. All MIG-seq data obtained in this study were deposited in the International Nucleotide Sequence Databases through the DNA Data Bank of Japan (DDBJ) [Sequence Read Archive (SRA) accession numbers DRX 639955 – DRX 639976]. A total of 95995598 raw reads [mean ± standard error (SE) = 2181718 ± 54249] were generated. After filtering out adapter sequences and low-quality reads, we retained 81452308 reads per individual (mean ± SE = 2181718 ± 54249). In total, 5252 SNPs (R = 0.3) and 1209 SNPs (R = 0.5) were detected from the 22 individuals. The ML phylogenetic tree recovered well-supported topologies that were consistent with the clades (Corallium, Hemicorallium, and Pleurocorallium) hypothesized by Tu et al. (2015), confirming that H. ryukyuense belongs to the Hemicorallium clade (Fig. 18 B). However, within the genus Hemicorallium, the interspecific tree topology was inconsistent across datasets with varying rates of missing data, and clear genetic differences between morphologically distinct species could not be identified (Fig. 18). Consistent with the phylogenetic tree results, the genetic distance analysis revealed that the genus Pleurocorallium exhibited larger distances compared to the other two genera, while smaller values were observed between Corallium and Pleurocorallium (Fig. 19). When calculating intra-generic and intraspecific genetic distances, the intra-generic distances within Hemicorallium were significantly smaller than those within Pleurocorallium [Tukey’s honestly significant difference (HSD) test, p <0.05]. Furthermore, the genetic distance within the genus Hemicorallium was greater than the intraspecific variation within C. japonicum (Tukey’s HSD test, p> 0.05), but significantly smaller than the intraspecific genetic distances of the two Pleurocorallium species (Tukey’s HSD test, p <0.05).	en	Nonaka, Masanori, Takata, Kenji, Yasuda, Nina (2025): A New Species of the Genus Hemicorallium (Cnidaria: Octocorallia: Scleralcyonacea: Coralliidae) Collected from Okinawa Island. Species Diversity 30 (2): 193-206, DOI: 10.12782/specdiv.30.193, URL: https://doi.org/10.12782/specdiv.30.193
