Hemicorallium jiaolongensis Hu, Zhang & Xu, 2025

Hu, Xuying, Zhang, Qian, Ge, Meiling, Li, Xinlong, Wang, Zongling, Zhang, Xuelei & Xu, Qinzeng, 2025, Two new species of deep-sea Red Corals (Coralliidae, Genus Hemicorallium Gray, 1867) from the western Indian Ocean, Zoosystematics and Evolution 101 (1), pp. 317-339 : 317-339

Hemicorallium jiaolongensis Hu, Zhang & Xu sp. nov.

Material examined.

Holotype • Partial colony consisting of a branch with a broken edge on the stem; collected from the Carlsberg Ridge in the western India Ocean on 13 June 2022; Located at 3°26'33.72"N, 64°6'2.75"E, depth 1696 m. Currently preserved at - 20 ° C in the Key Laboratory of Marine Eco-Environmental Science and Technology, First Institute of Oceanography, China with voucher number FIO-IND 72 - JLBEN 22005 . Due to the uncontrollable nature of deep-sea sample collection and preservation, a more detailed examination of another suspected sample could not be performed (Fig. 2 f – h ) and, therefore, no paratype was identified.

Description.

Colony. The specimen FIO-IND 72 - JLBEN 22005 is a branch of the colony, approximately 22 cm tall, with the base being the thickest at about 0.6 cm in diameter (Fig. 6 a ). All branches present dichotomous branching on one plane. The branches are slightly curved, with many thinner branchlets appearing. There are remains of tissue where a brittle star had been entwined around the branches (the brittle star has been removed).

Polys. The branchlets can hold up to 14 non-retractable autozooids. At the tips of the branchlets, there are pairs of symmetrical polyps forming a Y-shape. These autozooids are distributed only on one side of the colony, with some forming acute angles or being perpendicular to the plane of the colony (Fig. 6 b ). The autozooids are 3.312 ± 0.554 mm in height and 1.759 ± 0.147 mm in width, the height of them usually being greater than the distance between them. Siphonozooids are not easily observed and appear as tiny pores on the branches.

Axis. The surface of the coenenchyme is uneven, but lacks noticeable protrusions or depressions. The side without autozooids has slight longitudinal grooves (Fig. 6 b ). The axis is hard calcareous with no presence of canals inside (Fig. 6 c and Suppl. materials 7 – 9). The surface of the axis without coenenchyme reveals irregular, sharp projections (Fig. 6 h ).

Colour. In underwater in situ videos, it appears white to light yellow. The base of the colony is white. After being collected and brought on board, the fresh coenenchyme is light yellow. The axis exhibits a translucent milky white appearance (Fig. 6 c ) and sclerites observed under a microscope appear pale red.

Sclerites. Rods are mainly present in the tentacles and there are two main types: short rods with sharp and large radial projections (86.028 ± 15.155 μm in height, Fig. 7 a ) and long rods with small and blunt projections (112.769 ± 19.156 μm in height, Fig. 7 b ). Both types of rods have irregular small protrusions at both ends.

Crosses, 6 -, 7 - and 8 - radiates and irregular radiates are found in both the autozooids and the axis surface (coenenchyme). Crosses sclerites are rare (Fig. 7 c ) and only two sclerites were captured with different crossing angles. They measured 88.388 µm in height and 107.593 µm in width with nearly 90 ° angles and 73.350 µm in height and 60.283 µm in width with nearly 60 ° angles, respectively. The 6 - and 7 - radiates can be either symmetrical or asymmetrical (Fig. 7 d ), measuring approximately 65.837 µm to 92.7717 µm in length. The 8 - radiates are the most abundant, with two different types. The ends of the rays in a particular type of 8 - radiates consist of multiple sharp spikes (72.452 ± 8.572 µm in height, Fig. 7 e ). They have larger rays and gaps between them are hard to discern due to R 2, R 3, R 4 and R 5, R 6 and R 7 being tightly clustered together. Other 8 - radiates have smaller, but more pronounced rays with spaces between the eight rays (80.418 ± 10.907 µm in height, Fig. 7 f ). The irregular radiates (Fig. 7 i ) are about 45.257 µm to 103.113 µm in height and typically feature asymmetric shapes or excessively protruding rays. No double clubs have been found in this specimen.

Etymology.

This species, Hemicorallium jiaolongensis , is named in recognition of the manned submersible “ Jiaolong ”, which was instrumental in the collection of this specimens. The name honours the dedication and efforts of the Jiaolong crew during the scientific expedition in the western Indian Ocean.

Comparison.

Specimen H. jiaolongensis sp. nov. FIO-IND 72 - JLBEN 22005 exhibits all its polyps distributed on one side of the colony, with non-retracted autozooids and rod-shaped sclerites present in the tentacles. Therefore, this specimen aligns with the characteristics of the genus Hemicorallium and is classified within this genus.

The newly-described H. jiaolongensis sp. nov. features a distinct type of 8 - radiates that differentiates it from the closely-related Hemicorallium laauense Bayer, 1956 ( Bayer 1956; Tu et al. 2012; Nonaka and Hayashibara 2021), which also lacks double clubs. The rays of these 8 - radiates have sharp spikes at their ends. More notably, the gaps between the rays, except for R 1 and R 8, are very small, making the gaps between the rays hard to discern. In previously-recorded species of the genus Hemicorallium , the edges of the 8 - radiates typically have blunt spikes and clear gaps can be observed between the upper and lower halves (similar to those in Fig. 3 f ). Compared to all other reported species of the Hemicorallium genus that lack double clubs, H. jiaolongensis sp. nov. can be distinguished by its absence of spherical radiates which are present in Hemicorallium aurantiacum Tu, Dai & Jeng, 2016 ( Tu et al. 2016), Hemicorallium guttatum Tu, Dai & Jeng, 2016 ( Tu et al. 2016; Wei et al. 2024), Hemicorallium halmaheirense Hickson, 1907 ( Hickson and Versluys 1907; Tu et al. 2016), Hemicorallium imperiale Bayer, 1955 ( Bayer 1955) and Hemicorallium regale Bayer, 1956 ( Bayer 1956). Hemicorallium kaiyo Nonaka & Hayashibara, 2021 ( Nonaka and Hayashibara 2021) lacks rods with sharp projections and the crosses that are both present in H. jiaolongensis sp. nov. Hemicorallium reginae Hickson, 1905 ( Koninklijke Akademie van 1905; Tu et al. 2016) and Hemicorallium variabile Thomson & Henderson, 1906 ( Thomson et al. 1906) each possess their own unique irregular sclerites which are not found in H. jiaolongensis sp. nov. For more information on morphology comparisons, see Table 2 .

In summary, the remarkable morphological features that distinguish this new species from other members of the genus Hemicorallium include:

The taller (about 3 cm) and closely-spaced autozooids.

An uneven surface on the axis, characterised by sparse, fine and slightly sharp projections.

A particular type of 8 - radiates with sharp spikes on the edges and the middle rays of the radiates are tightly clustered together.

Remarks.

H. jiaolongensis sp. nov. represents a new species of Coralliidae first recorded in the Indian Ocean. Although no paratype is available, the features of another coral specimen, as observed through in situ videos and photographs, are highly similar to the holotype (Fig. 2 e – f and Suppl. material 5). This specimen also exhibits a white to light yellow colony with polyps distributed on one side. All small branches are numerous and densely packed.

Figures

Figure 2. In-situ images of deep-sea corals samples in this study. These images are from in-situ video screenshots and the camera on the Jiaolong. a. Sample in situ image of FIO-IND 72 - JLBEN 22003; b. Sample in situ image of NDSC-IND 72 - JLBEN 22001; c. Coral in the same area that was highly similar to FIO-IND 72 - JLBEN 22003; d. Sample in situ image of FIO-IND 72 - JLBEN 22005; e, f. Coral in the same area that was highly similar to FIO-IND 72 - JLBEN 22005.

Figure 3. Morphology of sclerites involved in this study and the diagram of radiates. a. Rods with sharp protrusions; b. Rods with blunt protrusions; c. Crosses; d. 6 - radiates; e. 7 - radiates; f. 8 - radiates with the rays closely spaced; g. 8 - radiates with the rays loosely spaced; h. The multilobular ornaments face of the double clubs; i. The enlarged rays face of the double clubs; j. The side view of the double clubs (both showing multilobular ornaments and enlarged rays); k. A simple diagram of 8 - radiates to show the direction of the eight rays, generated using the visualisation modelling software Sharp 3 D (version 5.661). Scale bar: 100 μm (a – j).

Figure 6. Morphological observation of Hemicorallium jiaolongensis sp. nov. FIO-IND 72 - JLBEN 22005 collected in the western India Ocean. Photographs by camera (a); Microscopic observations (b – d); Scanning Electron Microscope (SEM) observations (e – h). a. The colony of H. jiaolongensis sp. nov.; b. The front and back of a branch; c. The cross-section of the axis; d. The autozooid of H. jiaolongensis sp. nov.; e. The details of the tentacles on an autozooid; f. The axis of H. jiaolongensis sp. nov.; g. The cortex of the axis; h. The surface details of the axis. Scale bar: 10 cm (a); 5 mm (b); 1 mm (c, d); 100 µm (e, f); 200 µm (g); 50 µm (h).

Figure 7. Morphological scanning electron microscopy observations of sclerites in Hemicorallium jiaolongensis sp. nov. a, b. Rods sclerites from the tentacles; c. Crosses sclerites; d. 6 - and 7 - radiates from both the autozooids and coenenchyme; e, f. 8 - radiates from both the autozooids and coenenchyme; g. Some irregular multi-radiates sclerites. Scale bar: 100 μm.