Tubastraea coccinea Scott 1984:40 Balanophyllia ponderosa Lam et al. 2008:735 Tubastraea sp. 3 Arrigoni et al. 2014:678 Tubastraea tenuilamellosa Rowlett 2020:508 A new species of the sun coral genus Tubastraea (Scleractinia: Dendrophylliidae) from Hong Kong Yiu, Sam King Fung Chung, Sheena Suet-Wah Qiu, Jian-Wen Zootaxa 2021 2021-09-28 5047 1 1 16 8QBM5 Yiu & Chung & Qiu, 2021 Yiu & Chung & Qiu 2021 [151,460,1590,1617] Anthozoa Dendrophylliidae Tubastraea Animalia Scleractinia 2 3 Cnidaria species megacorallita sp. nov.  Synonymy     Tubastraea coccinea—  Scott 1984:40, fig.48.    Balanophyllia ponderosa—  Lam et al.2008:735, figs. 1C-D.    Tubastraeasp. 3—  Arrigoni et al.2014:678, figs. 11M-O.    Tubastraea tenuilamellosa—  Rowlett 2020:508.   Materials examined.  Holotype: TMBC030850, colony with 14 corallites, 62 mmin length and 25 mmin height.  Paratypes: TMBC030851, colony with 11 corallites, 51 mmin length and 24 mmin height;  TMBC030852, colony with 9 corallites, 42 mmin length and 23 mmin height;  TMBC030853, colony with 4 corallites, 16 mmin length and 11 mmin height.    Typelocality.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 mwater 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 mmin length and 11–25 mmin height. The corallites are elliptical ( 8–25 mmin GCD and 6.5–19 mmin 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 mmin GCD and 1–4 mmin LCD). The depth of the fossa ranges from 2.5 mmto 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  Tubastraeabecause 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  Tubastraeain 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. coccineaand  T. micranthusin 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. coccineaand  T. micranthus.  Tubastraea coccineaand  T. micranthushave 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 rDNAhas 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 Kongin 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),  Tubastraeasp. 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, IGRand rDNAgenes, respectively. These distances were equivalent or larger than the interspecific distances among  T. coccinea,  T. micranthusand Tubstreaeasp. 2, which supports the recognition of  T. megacorallitaas a new species.   FIGURE 2.Phylogenetic trees of the concatenated COI/IGR/rDNAsequence 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  Tubastraeaspp.    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  Tubastraeaspeciesin the NCBI and the sequences of specimens from this study (in bold).    1 2 3 4 5 6 7 8 9 10 11  1   Tubastraeasp. 1  (MY105)  2   Tubastraeacf. 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   Tubastraeasp. 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   Tubastraeasp. 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   Tubastraeasp. 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  Tubastraeaformed a monophyletic clade within Dendrophylliidae( Fig. 2). Among the seven species of  Tubastraeaused in this analysis,  T. megacoralllia  sp. nov.was nested among the other species and was sister to  Tubastraeasp. 3K12, 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. micranthusand Tubatraeasp. 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  Tubastraeasp. 3. Other species of  Tubastraeaare more distantly related to  T. megacorallita  sp. nov. [404,1433,1888,1915] TMBC 2 3 TMBC030850 1 holotype [151,1172,1924,1951] TMBC 2 3 TMBC030851 1 paratype TMBC 2 3 TMBC030852 1 paratype TMBC 2 3 TMBC030853 1 paratype [199,919,150,177] Hong Kong 22.461 Hong Kong 75 114.42 3 4 1 holotype