Tubastraea dendroida, Yiu & Qiu, 2022

Yiu, Sam King Fung & Qiu, Jian-Wen, 2022, Fig. 4 in Fig. 2 in Fig. 9 in Fig. 1 in Fig. 20. A-E in Establishment of A New Bornean Genus of Gecarcinucidae (Crustacea: Brachyura), with Descriptions of Five New Species., Zoological Studies 61 (45), pp. 1-12 : 3-10

Class ANTHOZOA Ehrenberg, 1834 Order SCLERACTINIA Bourne, 1900 Family DENDROPHYLLIIDAE Gray, 1847 Genus Tubastraea Lesson, 1830

Tubastraea dendroida sp. nov. ( Fig. 2 ) urn:lsid:zoobank.org:act:774c42bb-bd84-4f0f-b00f- 256ba8d1c90d

Materials examined: Holotype: Colony with

74 corallites, 60 mm in length and 94 mm in height

( TMBC 030974). Paratype: Colony with 74 corallites, 13.5 mm in length and 202 mm in height ( TMBC 030975).

Type locality: Both specimens were collected from Sung Kong (22°11'26.5"N, 114°16'48.4"E) on 28/09/2021 at 17 m depth ( Fig. 1 ).

Etymology: Tubastraea dendroida sp. nov. looks like a tree branch. The species epithet reflects this morphological character.

Geographic distribution: Currently only known in Hong Kong.

Habitat: Exposed sites with moderate current, rocky substrate, 10–25 m water depth.

Description: Living specimen ( Fig. 2A–C ) with bright orange tissue covering epithecal wall and corallite. Tentacles yellow, usually withdrawn. Colony dendroid, branching uniplanar, with one elongate, straight axial corallite, and several side branches formed by extra-tentacular budding ( Fig 2D ). Each specimen with up to 74 corallites varying between 13.5–60 mm in length and 94–202 mm in height. Colony height up to 50 cm. Corallites circular or slightly elliptical (6–8 mm in GCD and 5–7 mm in LCD) with a thin wall. Axial corallites usually biggest among all corallites in a colony. A total of 24 septa present, with 10 to 16 of the septa fused with columella ( Table 1). Septa hexamerously arranged ( Table 2), containing 3 cycles, with size increasing from inner to outer as S 1 = S 2> S 3. Septa usually arranged in a Pourtalès plan ( Fig. 2E ), curving from edge to columella. Columella ( Fig. 2E ) spongy (2–3 mm in GCD and 1–2 mm in LCD). Fossa 3–11 mm deep. Costae granular. Intercostal striae porous ( Fig. 2F ).

Taxonomic remarks: Tubastraea dendroida sp. nov. resembles T. micranthus and Dendrophyllia ijimai in that their colonies are uniplanar ( Filander et al. 2021). It can be distinguished from T. micranthus in that the latter has a slimmer main “stem”, its three septal cycles are not arranged a Pourtalès plan, and it is usually in dark green or brown colour ( Schuhmacher 1984; Cairns and Zibrowius 1997; Sammarco et al. 2010; Filander et al. 2021). However, Tachikawa (2005) reported that T. micranthus had both dark green and orange colour morphs in Japan, with the dark green morph more dominant. Whether this is true, or the orange morph is T. dendroida sp. nov. needs to be determined when specimens are available for examination. The septa of Dendrophyllia ijimai are also arranged in a Pourtalès plan, but this species differs from the new species in having four septal cycles instead of three septal cycles. It is the second species of Tubastraea known to have a Pourtalès plan.

Tubastraea chloromura sp. nov. ( Fig. 3 ) urn:lsid:zoobank.org:act:1d107473-b405-468f-9212- 8a2fe77db739

Materials examined: Holotype: Colony with 26 corallites, 45 mm in length and 32 mm in height ( TMBC030976 ).

Paratype: Colony with 16 corallites, 57 mm in length and 30 mm in height ( TMBC 030977).

Type locality: Both specimens were collected from Waglan Island (22°10'51.4"N, 114°18'11.8"E) on 14/03/2021 at 10 m depth ( Fig. 1 ).

Etymology: Tubastraea chloromura sp. nov. has a distinct olive green epithecal wall. The species epithet chloromura (Latin chloro = green, murus = wall) reflects this morphological character.

Geographic distribution: Currently only known in Hong Kong.

Habitat: Exposed sites with moderate current, rocky substrate.

Description: Living specimen ( Fig. 3A–B ) with olive green tissue covering epithecal wall of corallite, and light green tentacles. Colony phaceloid. Corallites formed by extratentacular budding ( Fig 3B ), consisting of 16–26 corallites. Colonies between 45–57 mm in length and 30–32 mm in height. Corallites circular (6–10 mm in GCD and 6–11 mm in LCD) with a thin wall. A total of 34–40 septa present, with 10 to 12 of the septa fused with columella ( Table 1). Septa hexamerously arranged ( Table 2), containing 4 cycles, with increasing size from inner to outer as S 1> S 2> S 3 = S4. Septa normally inserted. Septa spongy, highly porous ( Fig. 3D ). Columella ( Fig. 3D ) spongy (1.5–4 mm in GCD and 4–6 mm in LCD). Fossa 4–8 mm deep. Costae granular. Intercostal striae porous ( Fig. 3E ).

Taxonomic remarks: Tubastraea chloromura sp. nov. resembles T. coccinea in gross colony morphology, but its tissues are olive green. It was thought by the first author as a colour variant of T. coccinea when he collected the samples. This new species exhibits sympatric distribution with T. coccinea ( Fig 3A ). In addition to having a unique tissue colour, T. chloromura sp. nov. has a thinner and more porous septal texture than other Tubastraea species.

Tubastraea violacea sp. nov. ( Fig. 4 ) urn:lsid:zoobank.org:act:972E5F06-D434-45CB-8961-8CD65BC6DE38

Materials examined: Holotype: Colony with 130 corallites, 160 mm in length and 83 mm in height ( TMBC030978 ).

Paratype: Colony with 16 corallites, 35 mm in length and 40 mm in height ( TMBC 030979).

Type locality: The holotype was collected from Sung Kung (22°11'26.5"N, 114°16'48.4"E) ( Fig. 1 ) on 14/03/2021 at 10 m depth. The paratype was collected from Waglan Island (22°10'51.4"N, 114°18'11.8"E) on 28/09/2021 at 10 m depth.

Etymology: Tubastraea violacea sp. nov. has violet tissue covering the corallites. The species epithet reflects this morphological character.

Geographic distribution: Hong Kong (this study) and Canal Woodin, New Caledonia (based on the sequences of Tubastraea sp 2 . in Arrigoni et al. 2014)

Habitat: Exposed sites with moderate current, rocky substrate.

Description: Living specimen ( Fig. 4A ) with pale purple tissue covering epithecal wall, violet tissue covering corallite and translucent yellow tentacles. Colony phaceloid with each long corallite having its own wall. Corallites formed by extratentacular budding ( Fig. 4B ), consisting of 16–130 corallites. Colonies 35– 160 mm in length and 40–83 mm in height. Corallites cylindrical (10–18 mm in GCD and 8–14 mm in LCD) with a thick wall. A total number of 75–87 septa present, with 23–26 of the septa fused with columella ( Table 1). Septa hexamerously arranged ( Table 2), containing 5 cycles, with the size order of S1 = S 2> S 3> S 5> S 4. Septa arranged in a Pourtalès plan. Columella ( Fig. 4C ) spongy (6.0–8.0 mm in GCD and 2.5–4.0 mm in LCD). Fossa 9–11 mm deep. Costae granular. Intercostal striae porous ( Fig. 4D ).

Taxonomic remarks: Tubastraea violacea sp. nov. is unique among the congeneric species in having violet tissue covering the corallites. It is also remarkable in having a Pourtalès plan of septal arrangement, and that is the third species of Tubastraea has this character. Yiu et al. (2021a) observed that the Pourtalès plan is absent in small corallites of T. megacorallita but it is usually present in corallites at least 17 mm × 15 mm ( GCD × LCD) in size. However, all corallites of the type specimens of T. violacea sp. nov. were observed to exhibit a Pourtalès plan. Besides, the same as T. megacorallita , T. violacea sp. nov. has five septal cycles. All other Tubatraea species have three to four septal cycles. Moreover, T. violacea sp. nov. can be distinguished from T. megacorallita in having cylindrical corallites rather than elliptical corallites. Also, the two species are different in their septal size orders.

Molecular analyses

The alignment and concatenation resulted in a dataset of 1.733 bp ( COI: 601 bp, IGR: 448 bp, rDNA: 684 bp). Pair-wise sequence comparisons were conducted to determine the inter- and intra-specific p -distances ( Table 3). Intraspecific p- distances in the three species are in general very small, with 0% for COI, 0% for IGR, and 0.15% for rDNA in T. violacea sp. nov., 0% for COI, 0.22% for IGR, and 0% for rDNA in T. chloromura sp. nov., and 0% for COI, 0.22% for IGR, and 1.79% for rDNA in T. dendroida sp. nov. The relatively large rDNA p -distances between the two specimens of T. dendroida sp. nov. and between the two species of T. micrnthus indicate the potential of cryptic speciation in this species. Tubastraea violacea sp. nov. is most closely related to Tubastraea sp. 2 . HS2883, an undescribed species collected from Caledonia ( Arrigoni et al. 2014); the sequences between them had a p -distance of 0% for COI, 0% for IGR, and 0.32–0.48% for rDNA, indicating they are conspecific, despite their differences in tissue colour. The species closest to T. chloromura sp. nov. and Tubastraea dendroida sp. nov. is T. micranthus . Between T. chloromura sp. nov. and T. micranthus , the p -distance was 0.17% for COI, 0–0.22% for IGR, and 0.96% for rDNA. Between T. dendroida sp. nov. and T. micranthus , the p -distance was 0% for COI, 0–0.22% for IGR and 1.29–1.45% for rDNA. In comparison, the p -distance between T. micranthus and T. coccinea was 0% for COI, 0% for IGR and 1.29% for rDNA. Overall, these genetic distances support our designation of the three new species.

The ML and BI trees constructed using the concatenated sequences showed the same topology ( Fig. 5 ), with species of the genus Tubastraea forming a monophyletic clade within the family Dendrophylliidae . This result is in agreement with Arrigoni et al. (2014), and supports retention of the name T. aurea , rather than reclassifying the species as Australopsammia aurea ( Rowlett 2020) . Among the species of Tubastraea used in this analysis, T. dendroida sp. nov. is sister to T. chloromura sp. nov. The ( T. dendroida sp. nov. + T. chloromura sp. nov.) clade is sister to T. micranthus . Tubastraea violacea sp. nov. along with Tubastraea sp. 2 HS2883 are sister to Tubastraea sp. 2 HS2884. The (( T. violacea sp. nov. + Tubastraea sp. 2 HS 2883) +

Tubastraea sp. 2 HS 2884) clade is sister to T. coccinea .

Figures

Fig. 2. Tubastraea dendroida sp. nov.A–C, photographs of colonies taken in the field. D, skeleton of holotype (left, TMBC030974) and paratype (right, TMBC030975). E, Cross-sectional view of a corallite showing three septal cycles. F, lateral view of a corallite. Scale bars: A–C = 3 cm; D = 1 cm; E– F = 2.5 mm.

Fig. 1. A map of Hong Kong showing the two sampling sites in this study (red dots), as well as the sampling sites (triangles) of ahermatypic corals in previous studies (Scott 1984; Clark 1997; Lam et al. 2008; Yiu et al. 2021a).

Fig. 3. Tubastraea chloromura sp. nov. A, a colony of the new species (olive green) next to a colony of T. coccinea (red) in the field, a nudibranch Phestilla melanobranchia (pointed by a white arrowhead). B, a colony of the new species (olive green) next to a colony of T. coccinea (red) in laboratory aquarium. C, open polyp. D, skeleton of holotype. E, cross-sectional view of a corallite showing four septal cycles. F, lateral view of a corallite. Scale bars: A–B = 1 cm; C = 5 mm; D = 1 cm; E–F = 5 mm.

Fig. 4. Tubastraea violacea sp. nov. A, a colony of in the field and opened polyp at right top corner. B, open polyps. C, skeleton of part of the holotype (TMBC030978). C, cross-sectional view of corallite showing the five septal cycles. D, lateral view of a corallite. Scale bars:A–C = 1 cm; D– E = 5 mm.

Fig. 5. Phylogenetic tree of the concatenated COI/IGR/rDNA dataset constructed using the Maximum Likelihood method and Bayesian Inference method. Bootstrap values> 70 and Bayesian Inference posterior probability values> 0.7 are shown in the nodes. Data obtained in this study are indicated by an asterisk. # indicates the species name in Rowlett (2020) was Australopsammia aurea.