A new species of the sun coral genus Tubastraea (Scleractinia: Dendrophylliidae) from Hong Kong Author Yiu, Sam King Fung 0000-0001-6212-7339 Department of Biology and Hong Kong Branch of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Hong Kong Baptist University, Hong Kong, China & 20482205 @ life. hkbu. edu. hk; https: // orcid. org / 0000 - 0001 - 6212 - 7339 20482205@life.hkbu.edu.hk Author Chung, Sheena Suet-Wah 0000-0002-4575-4311 Department of Biology and Hong Kong Branch of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Hong Kong Baptist University, Hong Kong, China & sheena 98 @ connect. hku. hk; https: // orcid. org / 0000 - 0002 - 4575 - 4311 sheena98@connect.hku.hk Author Qiu, Jian-Wen 0000-0002-1541-9627 Department of Biology and Hong Kong Branch of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Hong Kong Baptist University, Hong Kong, China & Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, China & HKBU Institute of Research and Continuing Education, Virtual University Park, Shenzhen, China & qiujw @ hkbu. edu. hk; https: // orcid. org / 0000 - 0002 - 1541 - 9627 qiujw@hkbu.edu.hk text Zootaxa 2021 2021-09-28 5047 1 1 16 journal article 10.11646/zootaxa.5047.1.1 1175-5326 5533627 C6204F0A-006F-488F-AACA-6A72B299CBF1 Tubastraea megacorallita sp. nov. http://zoobank.org/NomenclaturalActs/fdcf7eaf-110d-40f6-b042-d39037e883d2 Synonymy Tubastraea coccinea — Scott 1984:40 , fig.48. Balanophyllia ponderosa — Lam et al. 2008:735 , figs. 1C-D. Tubastraea sp. 3 — Arrigoni et al. 2014:678 , figs. 11M-O. Tubastraea tenuilamellosa — Rowlett 2020:508 . Materials examined. Holotype : TMBC030850 , colony with 14 corallites, 62 mm in length and 25 mm in height . Paratypes : TMBC030851 , colony with 11 corallites, 51 mm in length and 24 mm in height ; TMBC030852 , colony with 9 corallites, 42 mm in length and 23 mm in height ; TMBC030853 , colony with 4 corallites, 16 mm in length and 11 mm in height . Type locality. Breaker reef ( 22.461°N , 114.420°E ), Hong Kong . Etymology. Tubastraea megacorallita sp. nov. has relatively large corallites when compared with its congeneric species. The species epithet reflects this morphological character. Geographical distribution. Currently only known in Hong Kong (this study) and Kii-Nagashima, Japan ( Arrigoni et al. 2014 ). Habitat. Exposed sites with moderate current, rocky substrate, at 10–25 m water depth. Description. When alive ( Fig 1a ), the tissue outside epithecal wall is light orange or pink and corallite bright red, and the tentacles are yellow and translucent. The colonies are phaceloid with each of the long corallite having its own wall. The corallites are formed by extratentacular budding ( Fig 1b ), consisting of 3 to 14 corallites. They vary between 16–62 mm in length and 11–25 mm in height. The corallites are elliptical ( 8–25 mm in GCD and 6.5–19 mm in LCD) with a thick wall. The total number of septa varies from 34 to 92, with 10–16 of the septa fused with columella ( Table 1 ). The number of septa increases as the corallites become bigger. The septa are hexamerously arranged, containing 5 cycles, the last cycle incomplete, with the sizes increasing from the inner to the outer as S 1 =S 2 >S 3 >S 4 =S 5 . The septa are usually arranged in a Pourtalès plan with the axial edges of pairs of higher cycle septa bending in front of and uniting before their adjacent lower cycle septum ( Fig. 1c ). The septa extend from the edge, curving down to the columella. The columella ( Fig.1d ) consists of a spongy network ( 2–10 mm in GCD and 1–4 mm in LCD). The depth of the fossa ranges from 2.5 mm to 10 mm . The costae are granulated and the intercostal striae are porous ( Fig.1e ) FIGURE 1. Tubastraea megacorallita . sp. nov. A: A living specimen in the field; B: Skeleton of a specimen with tissues removed (TMBC030850); C: a corallite (TMBC030853); D: Fossa (TMBC030853); E: Costae (c) and Intercostal striae (i.s.) (TMBC030853). Scale bar: A–B: 1 cm; C: 5 mm; D–E: 1 mm. Taxonomic remarks. Our specimens belong to the genus Tubastraea because it shares seven characters with congeneric species ( Cairns & Kitahara 2012 ): 1) corallum is colonial; 2), corallum is firmly attached; 3), corallum is encrusting; 4), multiple septa cycles are hexamerally arranged and spongy columella; 5), texture of corallum is rough; 6), number of coralla increases by budding from a common basal coenosteum, the connection among polyps is quite evident, and the septa are normally inserted; 7), columella is moderate to small in size and lacks epitheca. However, it is the only species of Tubastraea in which the septa are arranged in a Pourtalès plan. Morphologically, Tubastraea megacorallita sp. nov. can be easily distinguished from its congeneric species. It has five septal cycles and the septa are usually arranged in a Pourtalès plan, whereas the other seven species have only three to four septal cycles without a Pourtalès plan. Although T. megacorallita sp. nov. is most closely related to T. coccinea and T. micranthus in our molecular phylogenetic analysis, they differ substantially in corallite morphology ( Table 1 ). The corallites of T. megacorallita sp. nov. are larger than those of T. coccinea and T. micranthus . Tubastraea coccinea and T. micranthus have four and three septal cycles, respectively but T. megacorallita sp. nov. has five. Molecular analysis. Three gene sequences were successfully obtained from each of the three specimens .Alignment and concatenation resulted in a dataset of 1.683 bp ( COI : 601 bp, IGR : 450 bp, rDNA : 632 bp). Within the three partitions, only rDNA has adequate phylogenetic signal for species distinction. The uncorrected p -distances were 0% for all the three genes among the three individuals of T . megacoralllia sp. nov. collected from Hong Kong in this study ( Table 2 ). With a p -distance of only 0 for COI , 0 for IGR , and 0.21 or 0.41% for rDNA (KI2, KI3 respectively), Tubastraea sp. 3 . – an undescribed species collected from Kii-Nagashima, Japan ( Arrigoni et al. 2014 ) – is considered to be conspecific to T. megacorallita sp. nov. This new species exhibits 0–0.83%, 0–0.67% and 2.45–6.91% p -distance with other congeneric species in the COI , IGR and rDNA genes, respectively. These distances were equivalent or larger than the interspecific distances among T. coccinea , T. micranthus and Tubstreaea sp. 2, which supports the recognition of T. megacorallita as a new species. FIGURE 2. Phylogenetic trees of the concatenated COI/IGR/rDNA sequence dataset constructed using the Maximum Likelihood (left) and Bayesian Inference (right) method. Maximum Likelihood bootstrap values>50 and Bayesian Inference posterior probability values> 0.7 are shown in the nodes. Specimens used in this study are denoted by an asterisk. TABLE 1. Comparison of morphological characters between Tubastraea megacorallita . sp. nov. and other Tubastraea spp.

Characters	T. aureaa ,b	T. coccineac ,d,e,f	T. diaphanae ,h	T. faulknerd ,h,i
Growth form	Plocoid	Plocoid	Dendroid/Phaceloid	Plocoid
Intercorallite distance	Closely spaced	Closely/widely spaced
Corallites	Shape	Elliptical	Circular	Circular	Circular
LCD x GCD (mm)	12.0 x10.0	10.0-13.0	6.0-11.0	5.2-7.8/8.0-13.0
Columella	LCD x GCD (mm)/Size	2.0x1.0 -5.0x2.0	Large	Large
Fossa	Depth(mm)	6.0-7.0	Moderately deep	Deep	Deep and spongy/Shallow
Septa	Arrangement	Normal	Normal	Normal	Normal
Total number	Up to 48	48+
No. of septa fused with columella	12
Number of cycles	4 cycles	4 cycles	4 cycles	4 cycles
Size	S1=S2>S4>S3	S1>S2>>S3>S4; S1=S2>S4=S3	S1>S2>S4>S3
Fusion	S4 united with S3
Colour in living	Orangish red	Green-brown	Orange with yellow tentacles

.......continued on the next page TABLE 1. (Continued)

Characters	T. floreanah ,i	T. megacorallita sp. nov.	T. micranthuse ,j,k	T. tagusensisd ,i
Growth form	Phaceloid	Phaceloid	Dendroid/Branching uniplanar	Phaceloid
Intercorallite distance	Closely/widely spaced	Closely/widely spaced	Closely spaced
Corallites	Shape	Cylindrical	Elliptical	Circular	Cylindrical
LCD x GCD (mm)	4.0-6.0	6.3-19.1 x 8.0-24.6	4.5-6.5 x 5.0-7.5	<10.0
Columella	LCD x GCD (mm)/Size	Rudimentary	0.9-3.7 x 1.9-10.1	Rudimentary	Rudimentary
Fossa	Depth (mm)	4.0-5.0; moderately deep	2.5-18.1	4.0-9.0	Deep
Septa	Arrangement	Normal	Pourtalès plan	Normal	Normal
Total number	24	34-92	24/48
No. of septa fused with columella	10-26
Number of cycles	3 cycles	5 cycles	3 cycles	3 or 4 cycles
Size	S1=S2>S3	S1=S2>S3>S4=S5	S1>S2>>S3	S1=S2>S3>S4; S1=S2=S3>S4
Fusion	No	S5 fused with S4 and S3	No
Colour in living	Corallum: white; Polyps: bright pink	Orange, reddish, yellow	Dark green, brown black, red, orange	Polyps: lemon-yellow with red peristomes, pale red-violet, pale red violet with yellowish coenosarc

aSong (1982), bScott (1984), cWells (1983), dCairns (1991), eCairns & Zibrowius (1997), fCairns (1994), hLam et al . (2008), iWells (1982), jNemenzo (1960), kOgawa & Takahashi (1993) TABLE 2. Uncorrected COI / IGR / rDNA p -distances (%) calculated based on individual gene of the seven available Tubastraea species in the NCBI and the sequences of specimens from this study (in bold).

1	2	3	4	5	6	7	8	9	10	11
1	Tubastraea sp. 1
(MY105)
2	Tubastraea cf. aurea	1.16/0.45/7.27
(M762)
3	Tubastraea megacorallita	0.83/0.45/5.64	0.33/0.45/4.76
sp. nov.
(TMBC030850)
4	Tubastraea megacorallita	0.83/0.45/6.87	0.33/0.45/6.91	0/0/0
sp. nov.
(TMBC030851)
5	Tubastraea megacorallita	0.83/0.45/6.87	0.33/0.45/6.91	0/0/0	0/0/0
sp. nov.
(TMBC030852)
6	Tubastraea coccinea	0.83/0.45/4.95	0.33/0.45/5.87	0/0/2.45	0/0/3.9	0/0/3.9
(AQ2)
7	Tubastraea micranthus	0.83/0.45/5.57	0.33/0.45/6.66	0/0/4.39	0/0/5.18	0/0/5.18	0/0/1.67
(HS3129)
8	Tubastraea sp. 2	0.83/0.45/5.13	0.33/0.45/5.90	0/0/2.63	0/0/4.98	0/0/4.98	0/0/2.11	0/0/1.37
(HS2883)
9	Tubastraea sp. 3	0.83/0.45/6.23	0.33/0.45/6.27	0/0/0.18	0/0/0.21	0/0/0.21	0/0/3.93	0/0/4.51	0/0/5.04
(KI2)
10	Tubastraea sp. 3	0.83/0.45/5.88	0.33/0.45/6.54	0/0/0	0/0/0.41	0/0/0.41	0/0/3.49	0/0/3.99	0/0/4.41	0/0/0.41
(KI3)
11	Tubastraea diaphana	-/0.67/5.50	-/0.22/3.50	-/0.67/2.78	-/0.67/3.59	-/0.67/3.59	-/0.67/3.50	-/0.67/4.57	-/0.67/3.57	-/0.67/3.32	-/0.67/3.52
(AO101)

The ML and BI trees exhibited a very similar topology. Both the ML and BI trees showed that the genus Tubastraea formed a monophyletic clade within Dendrophylliidae ( Fig. 2 ). Among the seven species of Tubastraea used in this analysis, T. megacoralllia sp. nov. was nested among the other species and was sister to Tubastraea sp. 3 K12, an undescribed species from Kii-Nagashima, Japan ( Arrigoni et al . 2014 ). Together, they formed a clade that was sister to a clade containing T. coccinea , T. micranthus and Tubatraea sp. 2. However, it was not possible to determine which of these species is most closely related to the clade consisting of T. megacorallita sp. nov. and Tubastraea sp. 3 . Other species of Tubastraea are more distantly related to T. megacorallita sp. nov.