Expanding Knowledge of Sea Pen (Octocorallia: Pennatuloidea) Diversity and Distribution Through Integrative Taxonomy: Insights From Hong Kong's Coastal Waters
Bonnie Yuen Wai Heung, Yi‐Xuan Li, Hai Xin Loke, Keith Kei, Vincent C. S. Lai, Leo Lai Chan, Jian‐Wen Qiu
TL;DR
This study uses DNA and physical traits to identify nine sea pen species in Hong Kong, including three new ones, improving understanding of their diversity and distribution.
Contribution
The study introduces three new sea pen species and provides new DNA sequences and phylogenetic insights for Hong Kong's sea pens.
Findings
Nine sea pen species were identified in Hong Kong using molecular and morphological methods.
Three new species (Cavernularia solaris, Lituaria triscleromorpha, and Virgularia exilis) were described.
Phylogenetic analysis grouped the species into three well-supported clades.
Abstract
Sea pens (Octocorallia: Scleralcyonacea: Pennatuloidea) are widespread but remain under‐documented in the Northwest Pacific. Using a combined molecular (MutS‐ND2‐28S rRNA) and morphological approach, we analysed sea pen samples collected from Hong Kong's urban waters. MutS sequences at a 0.3% divergence threshold and ASAP automatic delimitation resolved nine species across three families and four genera for Hong Kong specimens, consistent with phylogenies inferred from concatenated datasets (MutS‐ND2‐28S rRNA), which recovered nine species in three well‐supported clades within Pennatuloidea. Morphological examinations (colony form, zooid arrangement, axis shape, sclerite shape and size) corroborated species boundaries. We described three new species (Cavernularia solaris sp. nov., Lituaria triscleromorpha sp. nov., and Virgularia exilis sp. nov.) and updated the morphological…
Genes, proteins, chemicals, diseases, species, mutations and cell lines named across the full text — each resolved to its canonical identifier and authoritative record.
Click any figure to enlarge with its caption.
FIGURE 1
FIGURE 2
FIGURE 3
FIGURE 4
FIGURE 5
FIGURE 6
FIGURE 7
FIGURE 8
FIGURE 9| Clade | Family |
| Max intra‐ | Min inter‐ |
|---|---|---|---|---|
| Clade 1 | Funiculinidae | 2 | 0 | NA |
| Scleroptilidae | 3 | 0 | NA | |
| Balticinidae | 2 | 0 | NA | |
| Pseudumbellulidae | 4 | 0 | 0.36 | |
| Gyrophyllidae | 4 | 0 | NA | |
| Kophobelemnidae | 6 | 0 | 0.54 | |
| Clade 2 | Virgulariidae | 6 | 0 | 1.81 |
| Protoptilidae | 2 | NA | NA | |
| Pennatulidae | 10 | 0.36 | 0.54 | |
| Stachyptilidae | 2 | NA | NA | |
| Echinoptilidae | 3 | 0.18 | NA | |
| Renillidae | 2 | NA | 1.45 | |
| Clade 3 | Anthoptilidae | 2 | NA | 1.08 |
| Umbellulidae | 6 | 0.18 | 0.72 | |
| Kophobelemnidae | 2 | NA | 7.32 | |
| Veretillidae | 21 | 0.18 | 3.9 | |
| Pennatulidae | 26 | 0.18 | 0.54 | |
| Virgulariidae | 30 | 0.18 | 0.36 |
- —Lantau Conservation Fund
- —Hong Kong Baptist University10.13039/501100001747
Peer Reviews
No public reviews on file for this paper yet. If you reviewed it on a platform where reviews are public (OpenReview, ICLR, NeurIPS, ICML), you can paste yours below so the community can read it here.
Videos
No videos yet. Explain this paper in a talk, walkthrough, or lecture? Add one.
Taxonomy
TopicsMarine Biology and Ecology Research · Crustacean biology and ecology · Ichthyology and Marine Biology
Introduction
1
Members of the superfamily Pennatuloidea Ehrenberg, 1834, often known as sea pens, are common inhabitants of the marine benthic environment. They occur from tropical to polar regions and from the intertidal zone to depths greater than 6100 m. Sea pens inhabit diverse habitats, including sand shores, mudflats, silty bottoms, and rocky outcrops, where they help structure benthic communities and provide habitats for other invertebrates (Williams 1992, 2011; Loke et al. 2025). Currently, Pennatuloidea includes 236 extant species in 16 families and 42 genera (McFadden, Cordeiro, Williams, et al. 2025).
Pennatuloids can be distinguished from other octocorals by a basal peduncle anchoring colonies into the substrate and by specialised polyp types, including oozooids, autozooids, siphonozooids, mesozooids, and acrozooids (Williams et al. 2012). Sea pens were classified as the order Pennatulacea Verrill, 1865, based on colony form, zooid arrangement, and sclerite characteristics (Kükenthal 1915; Hickson 1930; Bayer 1981), and a two‐suborder system was established (Sessiliflorae and Subselliflorae) (Kükenthal 1915). Williams (1995) questioned this system due to the paraphyly of Sessiliflorae and provided a dichotomous key for over 10 families and 30 genera.
Recent molecular studies have significantly advanced our understanding of the phylogenetic relationships of sea pens. Analyses of mitochondrial genes (mitochondrial mismatch repair gene—MutS and NADH dehydrogenase subunit 2—ND2) confirmed sea pens as a monophyletic group within Calcaxonia but indicated that traditional suborders and several families were not monophyletic (McFadden et al. 2006; Dolan et al. 2013). Molecular approaches combining mitochondrial and nuclear data have enabled the description of new taxa and refined evolutionary relationships (Kushida and Reimer 2019; García‐Cárdenas et al. 2020; López‐Gózalez et al. 2022; Hogan et al. 2023). A significant revision of Octocorallia, based on phylogenetic trees reconstructed using sequences from target‐capture of ultraconserved elements and exon loci as well as MutS, reclassified sea pens as the superfamily Pennatuloidea with 15 families under the order Scleralcyonacea (McFadden et al. 2022). Additionally, Pseudumbellulidae López‐González & Drewery, 2022 was erected as the sixteenth family for species that are morphologically similar to Umbellulidae Lindahl, 1874 (1840) but phylogenetically distinct from it (López‐González and Drewery 2022). Nonetheless, a comprehensive family‐level revision of Pennatuloidea remains pending, partly due to uneven taxon sampling across regions.
Hong Kong is situated on the southeastern coast of China, facing the Pearl River Estuary to the west and the South China Sea to the south and east. It lies in the subtropical waters of the Northwest Pacific, where knowledge of sea pen diversity is limited (Kushida and Reimer 2019). Despite its small sea area of 1651 km^2^, Hong Kong hosts over 25% of China's marine species (Ng et al. 2017). However, only five species from four families have been recorded from Hong Kong: Cavernularia obesa Valenciennes in Milne Edwards and Haime 1850 (Veretillidae), Pennatula fimbriata Herklots, 1858 (Pennatulidae), Pteroeides sparmannii Kölliker, 1869 (Pennatulidae), Sclerobelemnon burgeri (Herklots, 1858) (Kophobelemnidae), and Stachyptilum dofleini Balss, 1909 (Stachyptilidae) (Astudillo et al. 2024). This low diversity likely reflects a historical focus on rocky subtidal habitats and limited sampling of soft‐bottom‐dwelling sea pens (Qian et al. 2003; Fabricius and McCorry 2006; Yeung et al. 2014).
To address this gap, we included sea pens as a focal group in a study assessing epibenthic diversity of southern Hong Kong waters, sampling via bottom trawling and SCUBA diving across extensive muddy substrates. Additional specimens collected from western waters in the Pearl River Estuary, collected from another project, were included to enhance spatial coverage. These areas are distinct from the eastern waters, where the bottom is mainly rocky and scleractinian coral communities are better developed (Yeung et al. 2021; Loke et al. 2024). By employing an approach that combines molecular phylogenetic analyses (MutS, ND2, and 28S rRNA) with morphological examinations (sclerites, zooids, axis, and colony form), we aim to: (1) document the local sea‐pen fauna using integrative taxonomy by testing species boundaries with mitochondrial and nuclear markers; and (2) clarify their phylogenetic relationships. By generating new molecular data, revising diagnoses, and describing new species, our study contributes to the biodiversity inventory, distribution range, and systematics of sea pens in the Northwest Pacific.
Materials and Methods
2
Sampling
2.1
Between September 2021 and July 2023, we collected sea pen specimens from 28 sites around southern and western Hong Kong waters (Figure 1, Table S1) using trawling, grabbing, and SCUBA diving. From these specimens, we selected 48 specimens representing replicates of distinct morphospecies for examination (Figure 2, Table S2). Specimens were preserved in 95% ethanol and stored at −20°C. Holotype and paratype specimens (Table S2) were deposited in the South China Sea Marine Biodiversity Collection (SCSMBC), Chinese Academy of Sciences, Guangzhou.
Map of southern and western Hong Kong waters showing 27 sites with sea pen records. Blue lines indicate trawling tracks. Red and yellow dots indicate dive and grab sites, respectively.
Representative specimens of nine sea pen species examined. A. Pteroeides sparmannii (SCSMBC240235); B. Cavernularia obesa (SCSMBC240208); C. Cavernularia solaris sp. nov. (SCSMBC240215, holotype); D. Lituaria triscleromorpha sp. nov. (SCSMBC240218, holotype); E. Virgularia abies (SCSMBC240240); F. Virgularia gustaviana (SCSMBC240242); G. Virgularia exilis sp. nov. (SCSMBC240252, holotype); H. Virgularia sp. 10 (SCSMBC240250); I. Virgularia sp. 11 (SCSMBC240251). Scale bars: A–C, 30 mm; D–F, I, 50 mm; G, 100 mm; H, 10 mm.
DNA Extraction, PCR Amplification, Sequencing, and Raw Data Processing
2.2
Genomic DNA was extracted from the tissue samples using the QIAGEN DNeasy Tissue & Blood Kit (QIAGEN, Germany) following the manufacturer's protocol. DNA concentration and integrity were assessed using a NanoDrop ND‐2000 spectrophotometer (Thermo Fisher Scientific, USA) and 1% agarose gel electrophoresis. We amplified mitochondrial MutS (MutS‐like protein) with primers ND42599F (France and Hoover 2002) and Mut3458R (Sánchez et al. 2003), and ND2 (NADH dehydrogenase subunit 2) using primers 16S647F and ND21418R (McFadden et al. 2004). MutS and ND2 gene fragments were amplified following Sánchez et al. (2003) and McFadden et al. (2004), respectively. Amplicons were Sanger‐sequenced bi‐directionally at BGI (Shenzhen, China). DNA libraries of 11 selected specimens from nine species were prepared using the NEB Next Ultra DNA Library Prep Kit (New England Biolabs, MA, USA) according to the manufacturer's protocol at Novogene (Tianjin, China), and sequenced on an Illumina Novaseq 6000 to generate paired‐end 150‐bp reads.
Sanger sequences were assembled and trimmed using SeqMan Pro v.7.1.0 (DNASTAR Inc., Madison, WI, USA). Illumina reads were filtered using Trimmomatic v0.39 (Bolger et al. 2014) (parameters: LEADING = 3, TRAILING = 3, SLIDINGWINDOW = 4:15, MINLEN = 36). Clean reads were de novo assembled using SPAdes v3.13 (Bankevich et al. 2012) under default settings. Complete mitochondrial MutS and ND2, and nuclear 28S rRNA sequences were identified via BLAST+ v2.11.0 (Camacho et al. 2009) against available data on sea pens, with an e‐value cutoff of 1e‐10. The assembled MutS, ND2, and 28S rRNA were deposited in GenBank (Table S2).
Genetic Distances, Species Delimitation, and Phylogenetic Analyses
2.3
Since MutS provides greater genetic resolution at the species level in sea pens (McFadden et al. 2006; Dolan et al. 2013; Kushida and Reimer 2019), we compiled 134 MutS sequences, including 89 published pennatuloid sequences and 45 sequences from our study, to estimate genetic distances and delimit species. Pairwise Kimura 2‐parameter (K2P) distances (Kimura 1980) were calculated from a 560‐bp gap‐free MutS alignment using MEGA11 (Tamura et al. 2021), with 10,000 bootstrap replicates and gamma‐distribution rate variation (shape parameter = 4). Putative species were inferred using Assemble Species by Automatic Partitioning (ASAP) (Puillandre et al. 2021) based on the K2P distance matrix.
To infer relationships within Pennatuloidea, we compiled mitochondrial MutS and ND2, along with nuclear 28S rRNA sequences, from available species in the superfamily (Table S3). We included Junceella fragilis (GenBank accession number KJ541509 for mitochondrial MutS and ND2, and AF263355 for 28S rRNA) as the outgroup (Table S3). The phylogenetic analyses were conducted using PhyloSuite v1.2.3 (Xiang et al. 2023) with the following plug‐in programs. Sequences of each genetic marker were aligned using MAFFT v5 (Katoh and Standley 2013) under the ‘auto’ option and default settings. Gap regions of each alignment were trimmed using trimAl (Capella‐Gutiérrez et al. 2009) in ‘automated1’ mode. Two concatenated matrices were built: MutS‐ND2‐28S rRNA (4715 bp) and MutS‐ND2 (4230 bp). Best‐fit models were selected with ModelFinder v1.5.4 (Kalyaanamoorthy et al. 2017) under the Corrected Akaike Information Criterion (AICc). Maximum Likelihood (ML) phylogenies were inferred using IQ‐TREE v2.2.0 (Nguyen et al. 2015) under TVM + R4 + F (MutS‐ND2‐28S rRNA) and TVM + R3 + F (MutS‐ND2), with 10,000 ultrafast bootstraps (Minh et al. 2013) and the Shimodaira‐Hasegawa‐like approximation likelihood‐ratio support (Guindon et al. 2010). Bayesian Inference (BI) phylogenies for both concatenated datasets were performed using MrBayes 3.2.6 (Ronquist et al. 2012) under GTR + F + I + G4, with two parallel MCMC chains run for 10,000,000 generations, sampling every 1000 iterations and discarding 25% burn‐in. Convergence was verified using Tracer v.1.7.2 (Rambaut et al. 2018), with ESS > 250.
Morphological Observation
2.4
Species were identified using five key morphological characters: colony form, axis structure, autozooid and siphonozooid arrangement, and sclerite morphology (rachis, peduncle, and autozooids), following taxonomic criteria in d'Hondt (1984), Kükenthal (1915), Light (1921), and Williams (1989, 1995). Colonies were photographed with a Canon EOS 5D Mark IV camera fitted with an EF 100 mm f/2.8 L Macro IS USM lens or EF 24‐105 mm f/4 L IS II USM lens (Canon Inc., Japan). Polyp arrangements were examined and imaged under a Nikon SMZ1270 stereomicroscope (Nikon Corporation, Japan). Sclerites from the rachis, peduncle, and autozooids were extracted following the protocol of Williams and Mattison (2018), air‐dried, gold‐coated, and imaged with a LEO 1530 Field Emission Scanning Electron Microscope (GmbH, Germany).
Results
3
Genetic Distances
3.1
After quality filtering, 134 MutS sequences are retained for K2P distance calculation (Table S4) and ASAP analysis (Figure S1). Using a moderately conserved empirical threshold of 0.3% K2P for species‐level delimitation (intraspecific distance < 0.3%) (McFadden et al. 2014), the dataset resolves 74 genetic species; ASAP recovered a highly similar result with 73 putative species (Figure S1). Intraspecific variation is low across most taxa (0.00%–0.18%; Table 1), with a single Pennatulidae lineage in Clade 2 showing slightly higher variation (0.36%; Table 1). Given the concordance between methods, we adopted the 0.3% K2P threshold for the following presentation.
Within the Hong Kong material, nine species were recovered across four genera: one Pteroeides, two Cavernularia, one Lituaria, and five Virgularia.
For Pteroeides, our 18 P. sparmannii sequences are identical to one another and to Pteroeides sp. 6 YK219, collected from Shirato, Amakusa, Kumamoto, NW Pacific (Kushida and Reimer 2019) (Table S4). P. sparmannii differs from other available Pteroeides sequences by 0.54%–4.85% K2P (Table S4). For Cavernularia, our sequences recovered two lineages (Table S4): Cavernularia solaris sp. nov. (two identical sequences) and C. obesa (eight identical sequences). * Cavernularia solaris
- sp. nov. shows minimal divergence (0.00%–0.18%; Table S4) from sequences labelled “Cavernularia habereri” and “Cavernularia obesa” (collected from Incheon, South Korea, NW Pacific; Eom and Rhee 2023), indicating a single species, which is clearly distinct from other congeneric species (9.49%–21.88% K2P; Table S4). For Lituaria, our four Lituaria triscleromorpha sp. nov. sequences are identical (0.00% divergence; Table S4) and show no divergence from Veretillum sp. 1 YK96, collected from Kashiwajima, Kochi, NW Pacific (Kushida and Reimer 2019), indicating conspecificity with that reference lineage. Distances to other veretillids range from 0.36% to 10.12% (Table S4), consistent with species‐level divergence. Our C. obesa sequence shows 1.08% K2P divergence from the most closely related species, L. triscleromorpha sp. nov. (Table S4), further confirming their species‐level differences. For Virgularia, across 30 examined Virgularia sequences, intraspecific divergence is low (0.00%–0.18%; Table S4). Hong Kong sequences form five lineages (Table S4): (1) Virgularia abies (one sequence), (2) Virgularia gustaviana (nine identical sequences), (3) Virgularia exilis sp. nov. (one sequence), (4) Virgularia sp. 10 (one sequence), and (5) Virgularia sp. 11 (one sequence). These lineages are differentiated from other Virgularia by 0.36%–3.89% K2P (Table S4).
Phylogenetic Analyses
3.2
Phylogenetic analyses of concatenated MutS‐ND2‐28S rRNA and MutS‐ND2 datasets using Maximum Likelihood (ML) and Bayesian Inference (BI) consistently recover three major clades within Pennatuloidea across all estimated topologies (Figure 3; Figure S2). Although the relative placement of the three clades differs between BI (Clade 2 + (Clade 1 + Clade 3)) and ML (Clade 3 + (Clade 1 + Clade 2)) topologies, support for these alternative arrangements is low in BI (posterior probabilities, PP = 0.49 for MutS–ND2‐28S rRNA; PP = 0.54 for MutS–ND2; Figure S2). In contrast, ML topologies show a higher overall support for both datasets (ultrafast bootstrap, UFBoot ≥ 80; Figure 3 and Figure S2), with the MutS‐ND2‐28S rRNA matrix yielding a more strongly supported tree (UFBoot > 95, Figure 3) for the three main clade divisions than the MutS‐ND2 dataset (UFBoot ≥ 80; Figure S2). There are several conflicts among clades in ML topologies generated from two datasets (Figure 3; Figure S1). However, the MutS‐ND2‐28S topologies typically exhibit higher support for these conflict nodes (Figure 3) than the MutS‐ND2 topologies (Figure S2). For example, in the MutS‐ND2 tree, Distichoptilum gracile does not group with Ptilella (UFBoot = 51, PP = 0.36; Figure S2).
Maximum likelihood phylogenetic relationships of Pennatuloidea based on MutS‐ND2‐28S rRNA. Three major clades are labelled (Clades 1–3); the Bayesian‐inference topology for clade relationships is shown in the inset. All Hong Kong specimens belong to Clade 1 and are highlighted in bold red. Node support is shown as (Shimodaira‐Hasegawa approximate likelihood‐ratio/ML ultrafast bootstrap)/BI posterior probability; an asterisk inside parentheses indicates 100/100, a dash indicates Shimodaira–Hasegawa approximate likelihood‐ratio < 80, and a tilde denotes nodes where ML and BI relationships differ. Scale bar: 0.01 substitutions per site. Virgulariidae (Vi), Pennatulidae (Pe), Veretillidae (Ve), Kophobelemnidae (Ko), Scleroptilidae (Sc), Anthoptilidae (An), Renillidae (Re), Echinoptilidae (Ec), Stachyptilidae (St), Protoptilidae (Pr), Gyrophyllidae (Gy), Pseudumbellulidae (Ps), Balticinidae (Ba), Funiculinidae (Fu).
In the best topology (MutS–ND2‐28S rRNA; Figure 3), Clade 3 is the earliest diverging clade and comprises six families (UFBoot = 99) arranged as (Funiculinidae + ((Pseudumbellulidae + (Scleroptilidae + Balticinidae)) + (Kophobelemnidae + Gyrophyllidae))). Family‐level nodes are strongly supported (UFBoot > 97, PP > 0.97; Figure 3). Clade 2 consists of six families (UFBoot = 100, PP = 1; Figure 3) with the topology ((Stylatula + Protoptillidae) + (((Protoptillidae + Pennatulidae) + (Pennatulidae + Scytalium)) + ((Stachyptilidae + Pennatulidae) + (Echinoptilidae + (Renillidae + Pennatulidae))))) (Figure 3). Stylatula and Scytalium, traditionally placed within Virgulariidae, are distantly related to other Virgularidae sensu stricto recovered species in Clade 1 (Figure 3), suggesting a paraphyletic Virgulariidae pending morphological re‐evaluation. Paraphyly is also evident within Pennatulidae in Clade 2, which comprises multiple subclades, and with Pteroeides placed in Clade 1 (Figure 3), underscoring the need for familiar revision.
All nine Hong Kong species fall within Clade 1 (UFBoot = 100, PP = 1; Figure 3). Within Clade 1, we recover seven families with the topology ((((Scleroptilidae + Umbellulidae) + Anthoptilidae) + (Veretillidae + Kophobelemnidae)) + (Virgulariidae + Pennatulidae)). Among them, Anthoptilidae, Scleroptilidae, and Umbellulidae are monophyletic, while other families have paraphyletic relationships at the genus level, requiring further taxonomic investigation (Figure 3). Our material represents Pennatulidae, Veretillidae, and Virgulariidae (Figure 3). Five Hong Kong Virgularia species are closely related to congeners from Japan and Palau (UFBoot ≥ 98, PP ≥ 0.94) (Kushida and Reimer 2019; Figure 3; Table S3). Pteroeides forms a well‐supported lineage sister to the Glaciaptilum and Virgularia clade (UFBoot = 99, PP = 1; Figure 3), and Pteroeides sparmannii is identical to Pteroeides sp. 6 YK219 (UFBoot = 100, PP = 1; Figure 3), collected from Shirato, Amakusa, Kumamoto, NW Pacific (Kushida and Reimer 2019). The other specimens were identified as three species of Veretillidae (Figure 3). Notably, Cavernularia obesa SCSMBC240206 does not group with the aforementioned Cavernularia clade; instead, it falls with unidentified Veretillum and Cavernulina lineages, albeit with low support (BS < 40, PP < 30; Figure 3), highlighting the need for additional sampling and morphological validation. Lituaria triscleromorpha sp. nov. is recovered as sister to Veretillum sp. 1 YK96 (UFBoot = 98, PP = 1; Figure 3), collected from Kashiwajima, Kochi, NW Pacific (Kushida and Reimer 2019). Another species Cavernularia solaris sp. nov. forms a fully supported clade with sequences labelled “ C. obesa ” and “ C. habereri ” (UFBoot = 100, PP = 1), with a long branch length and deep divergence (9.49%–15.87% K2P) from other Clade 1 pennatuloids (Figure 3, S1, Figure S1, Table S4).
Systematics
Class Octocorallia Haeckel, 1866
Order Scleralcyonacea McFadden, van Ofwegen & Quattrini, 2022
Superfamily Pennatuloidea Ehrenberg, 1834
Family Pennatulidae Ehrenberg, 1834
Genus Pteroeides Herklots, 1858
** Pteroeides sparmannii Kölliker, 1869**
Zooid arrangements in taxa with polyp leaves. (A, B) Pteroeides sparmannii (SCSMBC240237): A, upper polyp leaf; B, lower polyp leaf. (C–E) Virgularia abies (SCSMBC240240): C, autozooid arrangement on polyp leaves (ventral view); D, siphonozooid arrangement (dorsal view); E, lateral view showing siphonozooids between polyp leaves. (F–H) Virgularia gustaviana (SCSMBC240242): F, autozooid arrangement (ventral); G, siphonozooid arrangement (dorsal); H, lateral view. (I–K) Virgularia exilis sp. nov. (SCSMBC240252, holotype): I, autozooid arrangement (ventral); J, siphonozooid arrangement (dorsal); K, lateral view. (L) Virgularia sp. 10 (SCSMBC240250), polyp leaf. (M–O) Virgularia sp. 11 (SCSMBC240251): M, autozooid arrangement (ventral); N, siphonozooid arrangement (dorsal); O, lateral view. Abbreviations: Autozooids (au), midline (ml), polyp leaf (pl), rays (r), siphonozooids (si). Scale bars: A, B, F, G, M, N, 5 mm; C, 3.5 mm; D, E, 2.5 mm; H, I, J, O, 2 mm; K, L, 1 mm.
Sclerites morphology of Pteroeides sparmannii (SCSMBC240235). A. Polyp leaves. B. Peduncle (surface). C. Peduncle (interior). Scale bars: A, 0.1 mm; B and C, 0.01 mm.
Pteroeides sparmannii Kölliker, 1869: 197, Figs. 42–43. Kükenthal, 1915: 101–102, Figure 110. Morton, 1983: 268, Figure 12.7. Imahara, 1996: 37.
Type locality: Unknown (not stated in original description).
Material examined: All specimens were collected from Hong Kong at 5–30 m depths. Off eastern Lantau Island: SCSMBC240220, N22.25882, E114.02422 to N22.24912, E114.02175; SCSMBC240221, N22.25827, E114.07680 to N22.26633, E114.06924; SCSMBC240223, N22.25920, E114.02303 to N22.24912, E114.02175; SCSMBC240225, N22.33928, E114.02623 to N22.34247, E114.03322; SCSMBC240232‐33, N22.27508, E114.05158 to N22.28337, E114.05352; SCSMBC240228: N22.33928, E114.02623 to N22.34247, E114.03322; SCSMBC240238: N22.27370, E114.05423 to N22.28053, E114.05573. Off southern Lantau Island: SCSMBC240222: N22.19412, E114.00225 to N22.19803, E114.00475; SCSMBC240227: N22.19283, E114.00422 to N22.19178, E114.00040; SCSMBC240237, N22.19568, E114.01604 to N22.19876, E114.00917. Off northern Lantau Island: SCSMBC240229‐31, SCSMBC240234, N22.34052, E114.02811 to N22.34258, E114.03670. Off southern Hong Kong Island: SCSMBC240224, N22.19193, E114.10202 to N22.19542, E114.07629; SCSMBC240226, N22.19200, E114.10290 to N22.19475, E114.09490; SCSMBC240239, N22.17456, E114.17207 to N22.17520, E114.16243. Between Lantau and Hong Kong Island: SCSMBC240235‐36, N22.27188, E114.07913 to N22.26683, E114.07362.
Description: Specimens length 45–122 mm; with across polyp leaves 29–65 mm. Polyp leaves rigid, broad medially, tapering apically and basally; opposite arrangement; feather‐like colony (Figure 2A). Colour light brown, with dark grey to black pigmentation between autozooids (Figure 4A,B). Peduncle with brown to black spotting in some specimens (Figure 2A). Axis circular in cross‐section; present throughout rachis and peduncle. Autozooids present on upper (Figure 4A) and lower (Figure 4B) polyp leaves, arranged in 3–4 irregular rows (2–3 rows in smaller colonies) (Figure 4A,B). Siphonozooids numerous on lower leaves (Figure 4B), absent on upper leaves (Figure 4A). Rays are prominent on polyp leaves, extending from base to slightly beyond margin (Figure 4A,B). Sclerites absent in rachis and autozooids. Sclerites in polyp leaves slender rods and needles, 0.1–3.2 mm long (Figure 5A). Peduncle sclerites minute ovals (~0.01 mm), denser at surface than interior (Figure 5B,C).
Distribution: Fuzhou, Hong Kong, Japan.
Remarks: Diagnostic features match Kölliker (1869): broad feather longer than peduncle, with rays extending only slightly beyond polyp leaves, autozooids in both upper and lower polyp leaves, siphonozooids restricted to lower polyp leaves, and numerous needle‐shaped sclerites in the autozooids zone. Our specimens are confidently classified as P. sparmannii based on their congruence with the holotype description. However, the original description lacked details on sclerites and the axis (Kölliker 1869). Kükenthal (1915) later described needle‐shaped sclerites (up to 0.3 mm) in the rachis surface and longer, thin rods (up to 0.2 mm) in the peduncle surface. However, our examination reveals a complete absence of sclerites in the rachis and the presence of only tiny oval sclerites in the peduncle (Figure 5B,C). Furthermore, we observed a circular axis in this species that was not documented in the previous literature. We therefore describe this species with details of the axis and the sclerites in the rachis and peduncle. This remains the sole Pteroeides species recorded from Hong Kong (Morton and Morton 1983).
Family Veretillidae Herklots, 1858
Genus Cavernularia Valenciennes in Milne Edwards & Haime 1850
** Cavernularia obesa Valenciennes in Milne Edwards & Haime 1850**
Sclerites morphology of Cavernularia obesa (SCSMBC240206) A. Rachis (interior). B. Rachis (surface). C. Peduncle (surface). D. Peduncle (interior). E. Peduncle (middle). Scale bars: A and B, 0.2 mm; C, D, and E, 0.1 mm.
Cavernularia obesa Valenciennes in Milne Edwards & Haime, 1850: lxxxiv. Kükenthal, 1915: 18, Figure 14. d'Hondt, 1984: 630–631, 634–635, 638. Williams, 1989: 296–297. López‐González et al., 2000: 207.
Veretillum contoriae Gray, 1862: 74–75.
Type locality: Indian Ocean
Material examined: All specimens were collected from Hong Kong at 4.8–15 m depths. Off eastern Lantau Island: SCSMBC240204, N22.23755, E114.04905 to N22.23187, E114.05583. Off southern Lantau Island: SCSMBC240208: N22.17846, E113.91310; SCSMBC240209: N22.19477, E114.00382 to N22.19244, E114.01560; SCSMBC240210‐11: N22.19412, E114.00225 to N22.19803, E114.00475. Off southern Hong Kong Island: SCSMBC240205: N22.23463, E114.10032 to N22.23168, E114.08992. Between Lantau and Hong Kong Island: SCSMBC240206‐07: N22.27188, E114.07913 to N22.26683, E114.07362.
Description: Specimens length 37–128 mm; width 20–27 mm. Most colonies clavate (Figure 2B), with grey‐white to pale yellow colour. Axis absent. Autozooids evenly distributed across rachis. Siphonozooids numerous, irregularly scattered among autozooids (Figure 2B). Autozooids sclerites absent. Rachis sclerites rods, some with bifurcate/spatulate ends, occasional flanged ends; outer layer 0.2–0.4 mm; inner layer 0.25–0.5 mm (Figure 6A,B). Peduncle sclerites stratified: surface layer rods and elongated ovals with slight central depressions (0.04–0.3 mm), some spindle‐like (Figure 6C); middle layer similarly forms, larger (0.08–0.52 mm) (Figure 6E); deep layer similar forms, smaller (0.05–0.45 mm) (Figure 6D).
Distribution: India, Indonesia, Australia, the Marquesas, China, Japan.
Remarks: Cavernularia obesa was established as the type species of Cavernularia by Valenciennes in Milne Edwards & Haime (1850). It is characterised by having no axis and autozooids sclerites, and having peduncle sclerites densely spaced, and needle‐like sclerites in the rachis. However, d'Hondt (1984) found that its rachis sclerites exhibit more morphological variation than previously described (Kükenthal 1915), including forms with bifurcate and spatulate ends, following re‐examination of the type material. Our observation aligns with this finding, while rachis sclerites with flanged ends are also occasionally observed (Figure 6A,B). However, the surface and interior peduncle sclerites in our specimens exhibit a larger size range than those described in López‐González et al. (2000). We therefore describe this species, with the following diagnostic features: a clavate colony lacking an axial structure; absence of autozooid sclerites; rachis sclerites as rods with bifurcate, spatulate, or flanged ends; and peduncle sclerites as elongated ovals and rods. C. obesa has previously been recorded in Hong Kong (Morton and Morton 1983). It can be distinguished from its only congener in the region, C. solaris sp. nov., by the absence of a central axis throughout the colony and by the distinct form of its rachis sclerites (bifurcate, spatulate, or flanged ends).
** Cavernularia solaris sp. nov **
urn:lsid:zoobank.org:act:1E18C1E2‐9478‐40AF‐A9CC‐6526117ACFAC
(Figures 2C, 7, S3A, Table S5)
Sclerites morphology of Cavernularia solaris sp. nov. (SCSMBC240215, holotype). A. Rachis (surface). B. Rachis (interior). C. Peduncle (surface). D. Peduncle (interior). Scale bars: A, B, C, and D, 0.1 mm.
Material examined: Holotype: SCSMBC240215, 1 whole colony, collected by J. W. Qiu on 6 March 2024 from western Lantau Island, Hong Kong (N22.25193, E113.83750 to N22.24043, E113.82860), depth 10–15 m. Paratypes: SCSMBC240212 and SCSMBC240214, 2 whole colonies, collected by V. C. S. Lai on 28 March 2023 from northern Lantau Island, Hong Kong (N22.34052, E114.02811 to N22.34258, E114.03670), depth 5–15 m. SCSMBC240213, 1 whole colony, collected by V. C. S. Lai on eastern Lantau Island, Hong Kong (N22.33928, E114.02623 to N22.34247, E114.03322), depth 5–15 m.
Diagnosis: Colony cylindrical to slightly clavate. Short axis between rachis and peduncle. Autozooids sclerites absent. Rachis sclerites spindle‐ and rod‐shaped. Peduncle sclerites rods, minute ovals, ovals with medial dents. Quadruplet sclerites present in lower rachis interior and peduncle interior.
Description: Specimens length 71–122 mm; width 13–15 mm. Colony cylindrical to slightly clavate (Figure 2C). Axis short, distinct in upper peduncle (23 mm in holotype) (Figure S3A). Autozooids evenly distributed on upper rachis; longitudinally arranged on lower rachis. Siphonozooids numerous, irregularly spaced (Figure 2C). Rachis surface with spindle‐shaped sclerites (0.16–0.44 mm) (Figure 7A). Rachis interior with rod‐like spindles, irregular ovals, and quadruplets (0.1–0.3 mm) (Figure 7B). Peduncle surface sclerites (0.04–0.18 mm) predominantly ovals (tiny ovals, elongated ovoids, obovoids) (Figure 7C). Peduncle interior with similar ovals (0.06–0.18 mm), plus quadruplets and irregular ovals (Figure 7D). Fresh specimens vibrant orange; tentacles white; retractable autozooids reddish‐brown.
Etymology: The Latin solaris (“of the sun”) refers to the vivid orange colouration of fresh colonies with white tentacles and reddish autozooids resembling solar flares.
Distribution: around Lantau Island in Hong Kong waters.
Remarks: Among the 16 described Cavernularia species, C. solaris sp. nov. resembles C. luetkenii Kölliker, 1872 from the Bay of Bengal in the Indian Ocean, sharing spindle‐shaped rachis sclerites (Figure 7A,B, Kölliker 1872) and oval‐dominated sclerites in the peduncle interior (Figure 7C,D, Kölliker 1872). However, C. solaris differs substantially in its distinct larger size (71–122 mm vs. 20–43 mm, Kölliker 1872; Thomson and Simpson 1906), axis location ( C. solaris in upper peduncle, Figure S3A, vs. C. luetkenii in base of rachis, López‐González et al. 2000), and presence of quadruplet sclerites throughout both lower rachis and peduncle interior (Figure 7B,C), whereas quadruplets are rare and restricted to rachis interior (Kölliker 1872). The new species can be confused with C. habereri Moroff, 1902, due to similar rachis surface sclerites (Table S5), but C. solaris has abundant rachis interior sclerites (absent in C. habereri ; Williams 1989; López‐González et al. 2000). In Hong Kong waters, C. solaris contrasts sharply with the only previously recorded congener ( C. obesa ) by the presence of a short axis, distinct sclerite morphology, and colouration (Williams 1989; López‐González et al. 2000; Table S5).
The discovery of C. solaris sp. nov. highlights the importance of comprehensive sclerite analysis (examining both surface and interior regions across rachis and peduncle) for differentiating Cavernularia species (Williams 1989; López‐González et al. 2000). The presence/absence and morphology of axial structures provide valuable diagnostic characters, as demonstrated by the clear distinction between axial C. solaris and anaxial C. obesa .
Genus Lituaria Valenciennes in Milne Edwards & Haime, 1850
Lituaria triscleromorpha sp. nov.
urn:lsid:zoobank.org:act:FA6CBCDB‐6FFC‐497A‐8BC8‐95759D881069
(Figures 2D, 8, S3B; Table S6)
Sclerites morphology of Lituaria triscleromorpha sp. nov. (SCSMBC240218, holotype). A. Polyp. B. Rachis (surface). C. Peduncle (interior). D. Peduncle (surface). Scale bars: A and B, 0.05 mm; C, 0.01 mm; D, 0.03 mm.
Material examined: Holotype: SCSMBC240218, 1 whole colony, collected by J. W. Qiu on 13 April 2022 from Kau Yi Chau, Hong Kong (N22.27188, E114.07913 to N22.26683, E114.07362), depth 5 m. Paratypes: SCSMBC240216, 1 whole colony, collected by V. C. S. Lai on 28 March 2023 from eastern Lantau Island, Hong Kong (N22.33928, E114.02623 to N22.34247, E114.03322), depth 5–15 m; SCSMBC240217, 1 whole colony, collected by V. C. S. Lai, on 22 March, 2023 from western Lamma Island, Hong Kong (N22.19193, E114.10202 to N22.19542, E114.07629), depth 5–15 m; SCSMBC240219, 1 whole colony, same data as holotype.
Diagnosis: Colony club‐shaped. Axis quadrangular with longitudinal furrows. Three sclerite zones: (1) autozooids with tuberculated/irregular sclerites; (2) rachis surface with denticulate/tuberculate club‐shaped sclerites with irregular ends; and (3) peduncle surface with denticulate club‐shaped plates with smooth and round ends, peduncle interior with minute ovals.
Description: Specimens length 115–139 mm; width 11–18 mm. Axis quadrangular axis with longitudinal furrows (Figure S3B); peduncle tapering distally to point. Autozooids irregularly distributed on rachis; denser in the upper half (Figure 2D). Siphonozooids densely and evenly arranged between autozooids (Figure 2D). Autozooids sclerites sculptured; irregularly divided ends and/or pointed protrusions (Figure 8A). Rachis interior without sclerites. Rachis surface with club‐shaped sclerites (0.09–0.12 mm) with tuberculated or denticulated surfaces and rounded/irregular ends; smoother texture than autozooid sclerites (Figure 8B). Peduncle surface sclerites club‐shaped plates (0.08–0.18 mm) with smooth rounded ends, surfaces smooth to denticulate/tuberculate (Figure 8D). Peduncle interior with sparse minute ovals (~0.01 mm; Figure 8C). Fresh specimens with brown rachis, white tentacles, brown/white autozooids, and greyish‐white peduncle (Figure 2D).
Etymology: From Latin tri‐ (“three”) + sclero‐ (“sclerites”) + −morpha (“forms”), referring to the three distinct sclerite morphologies.
Distribution: Hong Kong
Remarks: Among the nine recognised Lituaria species, L. triscleromorpha sp. nov. is distinguished by its unique tripartite sclerite zonation, despite sharing the characteristic quadrangular axis with congeners. It differs from L. kuekenthali Light, 1921, L. molle Light, 1921, L. philippinensis Light, 1921, and L. valenciennesi d'Hondt, 1984, which possess sclerites in only one of the rachis or peduncle (Table S6; Light 1921; d'Hondt 1984). In contrast, L. triscleromorpha sp. nov. exhibits sclerites in both structures, and it further contrasts with L. australasiae (Gray, 1860) and L. breve Light, 1921 by possessing peduncle surface sclerites (absent in those species). While L. hicksoni Thomson and Simpson, 1909 shows relatively uniform sclerites across autozooids, rachis, and peduncle (except for numerous ovals in the peduncle interior in large colonies; Thomson and Simpson, 1909), the new species exhibits pronounced zonation with distinct sclerite forms between these regions. Compared with L. phalloides (Pallas 1766), the description of unspecific sclerite zonation in the literature is complicated; however, the presence of minute crosses in L. phalloides (absent in the new species) (Thomson and Simpson, 1909) provides a key diagnostic difference. The validity of L. amoyenensis Koo, 1935 remains uncertain due to the loss of the type specimens and the lack of a detailed description.
This study highlights sclerite morphology as the primary diagnostic character for Lituaria species (Table S6). In L. triscleromorpha sp. nov., the distinct zonation of sclerite forms enables efficient differentiation from other congeners, underscoring the need for detailed morphological examinations in future taxonomic revisions, potentially integrated with molecular data.
Family Virgulariidae Verrill, 1868
Genus Virgularia Lamarck, 1816
** Virgularia abies (Kölliker, 1870)**
Halisceptrum abies Kölliker, 1870: 522
Virgularia abies Kükenthal, 1915: 75–76
Type locality: Japan
Material examined: SCSMBC240240, off northern Lantau Island (N22.34677, E113.89270), depth 2 m.
Description: Specimen incomplete. Rachis length 159 mm; width 5.5 mm. Axis rigid, round. Transverse polyp leaves slightly alternating, completely covering ventral rachis (Figures 2E and 4C). Autozooids slightly triangular (Figure 4C), 37–42 per polyp leaf; single row near leaf ends transitioning to double rows medially. Dorsal rachis with bare midline flanked by siphonozooids (Figure 4D). Siphonozooids in 3–4 rows between polyp leaves. (Figure 4E); not extending onto ventral rachis. Sclerites absent from rachis. Preserved specimen colour beige in ethanol (Figure 4E).
Distribution: Japan, Hawaii, Hong Kong.
Remarks: Virgularia abies, originally described by Kölliker (1869), was redescribed by Kükenthal (1915) with the following diagnostic features: an elliptical axis throughout the rachis, ~40 autozooids per leaf, and a distinct bare dorsal midline with bilateral siphonozooid fields on the rachis. Our specimen matches these features. This species is most similar to V. alba (Nutting 1912), sharing a comparable autozooid arrangement and number of autozooids per polyp leaf (Kölliker 1869; Kükenthal 1915; Nutting 1912; Table S7), but it differs by the absence of dorsal siphonozooids (present in V. abies). In Hong Kong, V. abies is the only species characterised by both triangular autozooids and a prominent bare midline on the dorsal rachis.
** Virgularia gustaviana (Herklots 1863)**
(Figures 2F, 4F–H, 9A,B, S4, Table S7)
Sclerites morphology of the interior peduncle in Vigularia. A. Virgularia gustaviana (SCSMBC240242). B. Virgularia gustaviana (SCSMBC240249). C. Virgularia sp. 10 (SCSMBC240250). Scale bars: A, B, and C, 0.01 mm.
Halisceptrum gustavianum Herklots 1863: 33–34
Virgularia gustaviana Kükenthal and Broch, 1911: 334. Kükenthal, 1915: 74–75, Figure 77. Hickson, 1916: 175–177. Williams, 1990: 91–94, Figs. 27, 28A,B.
Type locality: Xiamen
Material examined: All specimens were collected from Hong Kong at 2–15 m depths. Off northern Lantau Island: SCSMBC240241, N22.34052, E114.02811 to N22.34258, E114.03670; SCSMBC240247‐49, N22.34677, E113.89270. Off eastern Lantau Island: SCSMBC240243, N22.25880, E114.04068. Off southern Lantau Island: SCSMBC240242, N22.21497, E113.99788; SCSMBC240244‐45, N22.17846, E113.91310; SCSMBC240246, N22.19412, E114.00225 to N22.19803, E114.00475.
Description: Colony length 146–377 mm; width 4.5–16 mm. Axis quadrangular at rachis end, transitioning to circular between rachis and peduncle; gradual taper (Figure 2F). Opposite polyp leaves with 2–6 irregular rows of circular autozooids; number per leaf increasing with colony size, from 60 (SCSMBC240242, 150 mm colony) (Figure 4F,G) to > 200 (SCSMBC240248, 377 mm colony). Siphonozooids forming dense belt under polyp leaves (Figure 4H); extending onto dorsal rachis (Figure 4G). Sclerites present only in peduncle interior, as single or grouped ovals (Figure 9A,B). Fresh specimens colour: rachis/peduncle orange‐red, polyp leaves white/purplish.
Distribution: Indo‐West Pacific: Japan, China, Malay Archipelago, Indian Ocean, South Africa.
Remarks: V. gustaviana was originally described by Herklots (1863) and redescribed by Kükenthal and Broch (1911), Kükenthal (1915), Hickson (1916), Williams (1990) with the following diagnostic features: a quadrangular to circular axis, 50–200 autozooids per polyp leaf, a dense belt of siphonozooids beneath polyp leaves, evenly distributed siphonozooids on the dorsal rachis and oval sclerites in the peduncle interior. Hong Kong specimens conform to this diagnosis, but our largest specimens possess more than 200 autozooids per polyp leaf, and up to six rows of autozooids arranged in one polyp leaf. In Hong Kong, high autozooid counts and circular autozooids help distinguish V. gustaviana from other congeneric species (Table S7).
** Virgularia exilis sp. nov**.
urn:lsid:zoobank.org:act:8FC611B4‐BF3E‐4710‐BF1B‐FF873BD87F76
Material examined: Holotype: SCSMBC240252, 1 whole colony, collected by V. C. S. Lai on 28 March 2023 from Hei Ling Chau, Hong Kong (N22.25882, E114.02422 to N22.24912, E114.02175), depth 2 m.
Diagnosis: Colony very slender. Axis circular, poly leaves opposite, transverse. Autozooids 15–23 per polyp leaf; one to two rows on polyp leaf. Siphonozooids numerous on dorsum. Sclerites absent throughout colony.
Description: Colony length 330 mm; width 2.5 mm (Figure 2G). Axis circular. Rachis about five times peduncle length. Autozooids finger‐like, partially fused to form leaves (Figure 4I–K). Polyp leaves transverse and opposite, each with 15–23 autozooids. Autozoods near ventral side smaller than those near dorsal side (Figure 4I,J). Zooids near rachis end in single row. Siphonozooids one to two rows between the polyp leaves; inconspicuous (Figure 4K); numerous yet inconspicuous on dorsum (Figure 4J). Sclerites absent throughout colony. Colony pale brown in ethanol (Figure 2G).
Etymology: From Latin exilis (“slender”), referring to the narrow colony form.
Distribution: Hong Kong
Remarks: Among the 18 recognised Virgularia species, V. exilis sp. nov. is most similar to V. reinwardtii Herklots, 1858, sharing a circular axis, a similar number of autozooids per polyp leaf, and the absence of sclerites throughout the colony (Kölliker 1869; Kükenthal 1915). However, V. exilis sp. nov. differs in possessing numerous dorsal siphonozooids (Figure 4J), whereas V. reinwardtii has only two longitudinal rows of siphonozooids adjacent to each row of polyp leaves, without additional dorsal siphonozooids (Kölliker 1869; Kükenthal 1915). This new species may also be confused with V. juncea (Pallas 1766) and V. schultzei Kükenthal, 1910, due to overlapping autozooid counts per polyp leaf (Table S7). In contrast, the two species lack dorsal siphonozooids and possess minute oval sclerites (Kükenthal 1915). In Hong Kong, V. exilis sp. nov. is distinguished from congeners by its combination of 15–23 autozooids per polyp leaf and 1–2 rows of siphonozooids between leaves (Table S7).
** Virgularia sp. 10 sensu Kushida and Reimer, 2019**
Material examined: SCSMBC240250, Deep Bay, (N22.47577, E113.96117), depth 1 m.
Description: Colony very slender; length 73 mm; width 0.4 mm (Figure 2H). Axis circular. Polyp leaves are arranged oppositely (Figure 4L). Autozooids and siphonozooids arrangements not discernible due to small size (Figure 4L). Peduncle with bulbous end (Figure 2H). Sclerites minute ovals 0.003–0.007 mm (Figure 9C). Colour pale yellow in ethanol (Figure 2H).
Distribution: Palau, Hong Kong.
Remarks: The classification of this species is challenging due to its small size, which hinders analysis of zooid arrangements. However, molecular data indicate it is conspecific with Virgularia sp. 10 from Palau (Kushida and Reimer 2019), with a K2P genetic distance of 0.18%, within a species‐level threshold of 0.3% for sea pens (McFadden et al. 2014).
** Virgularia sp. 11 sensu Kushida and Reimer, 2019**
Material examined: SCSMBC240251, Sokos Island, Hong Kong (N22.17846, E113.91310), depth 2 m.
Description: Specimen incomplete, missing peduncle. Colony length 262 mm; width 12 mm. Axis quadrangular in rachis, circular in peduncle; gradually taper (Figure 2I). Polyp leaves opposite; 120–130 autozooids per leaf. Autozooids circular (Figure 4M–O). Siphonozooid inconspicuous between polyp leaves (Figure 4O); irregularly distributed on dorsal field (Figure 4N). Rachis and most polyp leaves white; some leaves tinged violet.
Distribution: Palau, Hong Kong
Remarks: This species is similar to V. gustaviana in axis shape, and zooid form and arrangement, but the missing of the peduncle precludes observation of sclerites. However, molecular data suggest this species is distinct from V. gustaviana (1.26%–1.45% K2P), but conspecific to Virgularia sp. 11 from Palau (Kushida and Reimer 2019).
Discussion
4
This integrative survey resolves nine species across three families, describes three new species, and provides new sequences that fill key gaps in Northwest Pacific taxon sampling, thereby strengthening regional inventories and biogeographic baselines for shallow‐water sea pens. By pairing MutS, ND2, and 28S rRNA with detailed assessments of colony form, axis structure, zooid arrangement, and sclerites, we delineate species with confidence and address the longstanding underdocumentation of sea pens in the region.
Species delimitation remains most robust when molecular and morphological evidence are evaluated together, particularly in genera with sparse sequence representation. Our study provides the first molecular data for Lituaria and a morphology‐based diagnosis for Lituaria triscleromorpha sp. nov., addressing deficits in taxon sampling noted for Northwestern Pacific sea pens (Kushida and Reimer 2019). The lack of type material and inadequate descriptions for its congener, L. amoyensis Koo, 1935, a species reported from Xiamen, preclude meaningful comparisons. We therefore treat L. amoyensis as a nomen dubium.
In Cavernularia, C. solaris sp. nov. and a sequence labelled “ C. habereri ” (GenBank: OK586148) share identical MutS, and “ C. obesa ” (OK149222) is genetically closer to C. solaris sp. nov. than to our morphologically confirmed C. obesa (9.18% K2P divergence) (Table S4). These mismatches highlight persistent identification errors in public databases and underscore the need for vouchered, integrative identifications. Within Virgularia, low intraspecific MutS variation in some species places greater diagnostic weight on zooid architecture, leaf arrangement, and axis morphology in our study, and suggests that a more sensitive genome‐wide approach, such as the UCEs (Quattrini et al. 2024), will be needed to refine species delimitation.
Our three‐clade framework (Figure 3) corroborates recent multilocus work showing that traditional suborders and several families are not monophyletic, reinforcing calls to revise Pennatuloidea at family and generic levels (Kushida and Reimer 2019; García‐Cárdenas et al. 2020; Hogan et al. 2023). Moreover, deep relationships among stem clades remain weakly resolved, with alternative ML/BI placements and short internodes suggesting rapid early divergences; this mirrors outcomes in prior sea pen phylogenies and points to the need for denser taxon sampling and phylogenomic datasets to stabilise the backbone topology (Kushida and Reimer 2019; García‐Cárdenas et al. 2020; Hogan et al. 2023). Within Pennatulidae, Veretillidae, and Virgulariidae, the recovered polyphyly/paraphyly adds independent support for reassessing family boundaries, especially in shallow‐water Northwestern Pacific lineages where morphological convergence is common. The close placement of Lituaria triscleromorpha sp. nov. with Veretillum sp. 1 suggests that some veretillid generic limits may require redefinition as broader taxon coverage becomes available; our new sequences reported here provide a foundation for that re‐evaluation.
Biogeographically, matching Hong Kong specimens to Pteroeides and Virgularia lineages previously known only from Japan and Palau, respectively, demonstrates regional connectivity and extends documented ranges, refining distribution maps for multiple taxa in the Northwest Pacific (Kushida and Reimer 2019; García‐Cárdenas and López‐González 2023). A plausible dispersal pathway links Palau to Hong Kong via the westward‐flowing North Equatorial Current, with subsequent northward transport by the Kuroshio Current; seasonal Kuroshio intrusions through the Luzon Strait facilitate exchange with the South China Sea, and interaction with the Taiwan Strait Current can carry larvae from Hong Kong toward Japan (Qiu 2002; Liang et al. 2003; Rudnick et al. 2015; Lin et al. 2025). Such current‐mediated dispersal, involving potentially long‐lived planktonic larvae, can produce the broad geographic ranges observed in these genera (Williams 2011). The discovery of nine species, including three new to science, highlights Hong Kong's soft‐bottom habitats as a regional node for shallow‐water sea pen diversity. This complements recent integrative work on the territory's rocky reefs, which has revealed hidden octocoral and scleractinian coral diversity and underscores the value of coordinated molecular–morphological approaches (Li et al. 2025; Yiu and Qiu 2022). More broadly, our results align with emerging syntheses that show sea pen diversity comprises both widespread taxa and geographically structured lineages shaped by habitat availability and environmental gradients, with ongoing revisions revealing expanded distributions and novel clades, including rock‐inhabiting forms discovered via phylogenomics (García‐Cárdenas and López‐González 2023; Ganguly and France 2024).
Conclusion
5
This study advances Northwestern Pacific sea pen systematics by resolving species boundaries with integrative data, naming three new species, contributing the first molecular sequences for Lituaria, and documenting range connections from Hong Kong to Japan and Palau, thereby addressing recognised regional gaps in diversity and distribution knowledge. The curated sequences and revised diagnoses are an immediate reference for taxonomy, ecological monitoring, and biogeographic analyses in Pennatuloidea, and provide resources for future work that will reassess family‐level relationships and generic placements across the Northwest Pacific. Given persistent non‐monophyly and uncertain deep nodes, expanded regional sampling, especially of under‐surveyed soft sediments, combined with phylogenomic approaches, is recommended to refine backbone relationships and stabilise classification. Hong Kong's demonstrated capacity to reveal hidden octocoral diversity makes it a strategic focal area for future integrative studies that will further clarify sea pen diversity and distribution throughout the Northwest Pacific.
Author Contributions
Bonnie Yuen Wai Heung: data curation (lead), formal analysis (lead), investigation (lead), writing – original draft (lead). Yi‐Xuan Li: formal analysis (equal), writing – review and editing (equal). Hai Xin Loke: data curation (equal), writing – review and editing (equal). Keith Kei: writing – review and editing (equal). Vincent C. S. Lai: writing – review and editing (equal). Leo Lai Chan: writing – review and editing (equal). Jian‐Wen Qiu: conceptualization (equal), methodology (equal), resources (equal), supervision (equal), writing – review and editing (equal).
Funding
This work was supported by Lantau Conservation Fund (LCF/RE/2021/05).
Conflicts of Interest
The authors declare no conflicts of interest.
Supporting information
Table S1: Sampling locations and metadata for sea pen collections. Table S2: Sea pen specimens examined and voucher information. Table S3: GenBank accession numbers and metadata for mitochondrial genome, MutS, ND2 and 28S rRNA sequences used in phylogenetic analyses. Table S4: Pairwise K2P distances (%) based on MutS for Hong Kong specimens and reference Pennatuloidea. Table S5: Diagnostic features for 17 species of Cavernularia (adapted and updated from López‐González et al. 2000). Table S6: Diagnostic features for nine species of Lituaria. Table S7: Diagnostic features for 18 species of Virgularia.
Figure S1: ASAP species delimitation results based on MutS. Colouration indicates the grouping of species. The red box denotes the grouping with the highest rank and the lowest ASAP score. Figure S2: Maximum likelihood phylogenetic relationships of Pennatuloidea based on MutS‐ND2. Three major clades are labelled (Clades 1–3); the Bayesian‐inference topology for clade relationships is shown in the inset. All Hong Kong specimens belong to Clade 1 and are highlighted in bold red. Node support is shown as (Shimodaira‐Hasegawa approximate likelihood‐ratio/ML ultrafast bootstrap)/BI posterior probability; an asterisk inside parentheses indicates 100/100, a dash indicates Shimodaira‐Hasegawa approximate likelihood‐ratio < 80, and a tilde denotes nodes where ML and BI relationships differ. Scale bar: 0.01. Abbreviations: Virgulariidae (Vi), Pennatulidae (Pe), Veretillidae (Ve), Kophobelemnidae (Ko), Scleroptilidae (Sc), Anthoptilidae (An), Renillidae (Re), Echinoptilidae (Ec), Stachyptilidae (St), Protoptilidae (Pr), Gyrophyllidae (Gy), Pseudumbellulidae (Ps), Balticinidae (Ba), Funiculinidae (Fu). Figure S3: Axis morphology of the two new species described in this study. A. Cavernularia solaris sp. nov. (SCSMBC240215, holotype), axis in the uppermost part of the peduncle interior. B. Lituaria triscleromorpha sp. nov. (SCSMBC240219, paratype), quadrangular axis with a side groove and a pointed end. Scale bars: A, 10 mm; B, 30 mm.
The reference list from the paper itself. Each links out to its DOI / PubMed record.
- 1Astudillo, J. C. , G. A. Williams , K. M. Y. Leung , et al. 2024. “Pennatuloidea Ehrenberg, 1834. Hong Kong Register of Marine Species.” https://www.marinespecies.org/hkrms/aphia.php?p=taxdetails&id=1609360.
- 2Bankevich, A. , S. Nurk , D. Antipov , et al. 2012. “SP Ades: A New Genome Assembly Algorithm and Its Applications to Single‐Cell Sequencing.” Journal of Computational Biology 19, no. 5: 455–477. 10.1089/cmb.2012.0021.22506599 PMC 3342519 · doi ↗ · pubmed ↗
- 3Bayer, F. M. 1981. “Key to the Genera of Octocorallia Exclusive of Pennatulacea (Coelenterata: Anthozoa), with Diagnoses of New Taxa.” Proceedings of the Biological Society of Washington 93, no. 3: 902–947.
- 4Bolger, A. M. , M. Lohse , and B. Usadel . 2014. “Trimmomatic: A Flexible Trimmer for Illumina Sequence Data.” Bioinformatics 30, no. 15: 2114–2120. 10.1093/bioinformatics/btu 170.24695404 PMC 4103590 · doi ↗ · pubmed ↗
- 5Camacho, C. , G. Coulouris , V. Avagyan , et al. 2009. “BLAST+: Architecture and Applications.” BMC Bioinformatics 10: 421. 10.1186/1471-2105-10-421.20003500 PMC 2803857 · doi ↗ · pubmed ↗
- 6Capella‐Gutiérrez, S. , J. M. Silla‐Martínez , and T. Gabaldón . 2009. “trim Al: A Tool for Automated Alignment Trimming in Large‐Scale Phylogenetic Analyses.” Bioinformatics 25, no. 15: 1972–1973. 10.1093/bioinformatics/btp 348.19505945 PMC 2712344 · doi ↗ · pubmed ↗
- 7d'Hondt, M. J. 1984. “Contribution à la connaissance de certains genres de la famille Veretillidae (Pennatulacea): Description de Cavernulma grandiflora n. sp. et de Lituaria valenciennesi nom. nov.” Bulletin du Muséum National D'histoire Naturelle 6: 625–640.
- 8Dolan, E. , P. A. Tyler , C. Yesson , and A. D. Rogers . 2013. “Phylogeny and Systematics of Deep‐Sea Sea Pens (Anthozoa: Octocorallia: Pennatulacea).” Molecular Phylogenetics and Evolution 69, no. 3: 610–618. 10.1016/j.ympev.2013.07.018.23906600 · doi ↗ · pubmed ↗