Hemicorallium kaiyo Nonaka & Hayashibara 2021, sp. nov.
Creators: name: Nonaka, Masanori
name: Hayashibara, Takeshi
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Cnidaria
Anthozoa
Alcyonacea
Coralliidae
Hemicorallium
Hemicorallium kaiyo

description: Hemicorallium kaiyo sp. nov.   (Figs 43–48; Tables 2, 7)  
 Material examined. Holotype, NSMT-Co 1737, Koko Seamount, 409–942 m, 14 June 2011.   
 Diagnosis. Colony may branch almost in one plane,   
without anastomoses, but colony form is unknown. Branching is irregular, at acute angles. Contracted autozooids are concentrated on the terminal twigs, interpolypar distance 1–3 mm, diameter 0.8–1.5 mm (average 1.06 mm) and height 0.7–1.3 mm (average 1.0 mm). Coenenchyme is 0.05–0.12 mm (average 0.08 mm) thick in the dry condition, without small warts, pale red in color. Axis stout, having many commensal burrows, no depressions underneath autozooids, smooth surface, red. Tentacles contain rods (about 0.1 mm long), coenenchyme contains 6-, 7-, and 8-radiates. Multi-radiates are rare, and double-clubs are absent.  
 Description of the holotype. Colony form. The specimen is a branch tip with some twigs (Fig. 43). It is about 50 mm long and 20 mm wide. Branch diameter is 4–5 mm, terminals 1–2 mm. It is presumed that branching is almost in one plane, without anastomoses, but the colony form is unknown. The angle of branching is acute (Fig. 43). Two commensal brittle stars were found on the branch.   
Polyps. The autozooids are not retracted into the coenenchyme, making cylindrical mounds with 8 inconspicuous longitudinal striations. They tend to concentrate on the terminal twigs, but not in clusters (Fig. 43). Autozooids are 1.06± 0.13 mm in diameter and 1.00± 0.19 mm in height (Table 2), distributed at 1–3 mm intervals on the twigs (Fig. 44). Siphonozooids cannot be found in this specimen.  
Axis. The surface of the stem of the axis is smooth and the twigs of the axis have shallow longitudinal grooves (Figs 45, 46). The grooves are distributed at about 0.34 mm intervals (Table 2). There are no rounded pits on the surface of the axis at the position of each autozooid. Many polychaete burrows are found in the axis, with some polychaetes visible by microscope (Fig. 45).  
Coenenchyme. The coenenchyme is very thin, 0.08± 0.03 mm and smooth, covering the axis (Figs 45, 46; Table 2). There are no warts on its surface (Figs 45, 46). At high magnification, the gastrovascular system is visible through it (Fig. 45).  
Color. The dry coenenchyme is pale red, the axis a deeper red color (Figs 43–46).  
Sclerites. The tentacles contain mainly rods (60%; 0.102± 0.014 mm long, 0.028± 0.004 mm wide), multi-radiates (27%; 0.084± 0.014 mm long, 0.036± 0.006 mm wide) and a few 7-radiates, 8-radiates and others (Figs 47, 48; Table 7).  
The autozooid mounds contain mainly symmetric 6-radiates (25%; 0.058± 0.008 mm long, 0.039± 0.005 mm wide), symmetric 8-radiates (20%; 0.068± 0.011 mm long, 0.041± 0.004 mm wide), 7-radiates (18%; 0.062± 0.009 mm long, 0.039± 0.005 mm width), and some asymmetric 6-radiates, asymmetric 8-radiates, multi-radiates are present (Figs 47, 48; Table 7).  
The branch tips contain mainly symmetric 8-radiates (29%; 0.061± 0.006 mm long, 0.039± 0.004 mm width), 7-radiates (26%; 0.057± 0.008 mm long, 0.039± 0.004 mm width), asymmetric 8-radiates (18%; 0.061± 0.006 mm long, 0.040± 0.003 mm width), symmetric 6-radiates (15%; 0.058± 0.006 mm long, 0.039± 0.004 mm width), and a few asymmetric 6-radiates and multi-radiates (Figs 47, 48; Table 7).  
The coenenchyme at the base of the colony contains mainly symmetric 8-radiates (39%; 0.059± 0.006 mm long, 0.038± 0.003 mm wide), 7-radiates (22%; 0.053± 0.006 mm long, 0.035± 0.004 mm wide), asymmetric 8-radiates (16%; 0.056± 0.006 mm long, 0.036± 0.003 mm width) and symmetric 6-radiates (13%; 0.053± 0.006 mm long, 0.037± 0.004 mm width). There are a few asymmetric 6-radiates and multi-radiates (Figs 47, 48; Table 7).  
 Etymology. The survey at the Emperor Seamounts was conducted by the Fisheries Agency research vessel “ Kaiyomaru ”. This species is named “kaiyo” from the name of the vessel, to give thanks to the Kaiyo-maru crew who collected the specimens studied here.   
 Remarks. Specimen NSMT-Co 1737 has non-retract- ed, cylindrical autozooids (Figs 45, 46), slender rod-shaped sclerites in the tentacles (Fig. 47), and lacks rounded pits on the surface of the axis at the position of each autozooid, thus belonging in the genus Hemicorallium.   
 There are only two species in the Pacific Hemicorallium previously described as having small contracted autozooids about 1.0 mm in both height and diameter: H. laauense and H. taiwanicum (Tu, Dai, and Jeng, 2012). However, H. laauense has both axis and coenenchyme whitish in color, and H. taiwanicum has an orange axis and dark-pink coenenchyme. Both species have no (or rare) 6-radiates in their coenenchyme, but NSMT-Co 1737 has about 25% 6-radiates (Figs 47, 48; Table 7). The color of the axis of this specimen   
 330 M. Nonaka and T. Hayashibara is the reddest encountered in this collection, comparable to that of C. japonicum. However, it seems unsuitable for ornamental use because of the numerous burrows in the axis (Fig. 45).
description: Published as part of Nonaka, Masanori & Hayashibara, Takeshi, 2021, A Report on Coralliidae (Cnidaria: Octocorallia) Specimens Collected from the Emperor Seamounts with Descriptions of Three New Species, pp. 297-342 in Species Diversity 26 on pages 327-330, DOI: 10.12782/specdiv.26.297, http://zenodo.org/record/5739111