Research Article |
Corresponding author: Tzu-Hsuan Tu ( thtu@mail.nsysu.edu.tw ) Academic editor: Bert W. Hoeksema
© 2022 Tzu-Hsuan Tu, Chang-Feng Dai.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Tu T-H, Dai C-F (2022) A new species of anthothelid octocoral (Cnidaria, Alcyonacea) discovered on an algal reef of Taiwan. ZooKeys 1089: 37-51. https://doi.org/10.3897/zookeys.1089.77273
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A molecular phylogenetic analysis of 132 octocoral species reveals a close relationship between specimens collected from the intertidal pools of the Datan Algal Reef, Taoyuan, Taiwan, and Erythropodium caribaeorum (Duchassaing & Michelotti, 1860), but the two species have distinct morphological features. On the basis of morphological differences in polyps and sclerites, we identify and describe a new Erythropodium species: E. taoyuanensis sp. nov. The distinct identifying features of E. taoyuanensis sp. nov. include the upright contractile polyps from thin encrusting membranes and abundant 6-radiate sclerites. Using an integrative approach, we present the findings of morphological comparisons and molecular phylogenetic analyses to demonstrate that E. taoyuanensis sp. nov. is distinct from other Erythropodium species. Our study contributes to the knowledge of octocoral biodiversity in marginal habitats.
28S rDNA, Anthothelidae, cox2-IGR-cox1, molecular phylogeny, msh1, northwestern Pacific, Scleraxonia
The Datan Algal Reef located in northwestern Taiwan, which occupies the intertidal flat toward the sublittoral along the 27-km long coastline of Taoyuan City, is composed of crustose coralline algae. Both sandy and muddy habitats occur in a mosaic pattern within the algal reef (
Meanwhile, the Datan Algal Reef is currently facing destruction from the development and construction of liquefied natural gas (LNG) storage terminals and ports by the Taiwan Chinese Petrol Corporation (CPC). Therefore, multiple environmental impact assessment surveys have been conducted. The intertidal surveys led to the discovery of a species of Erythropodium Kölliker, 1865 in the tidal pools (
Erythropodium is a genus of shallow water soft corals forming endosymbiotic association with Symbiodiniaceae belonging to the family Anthothelidae Broch, 1916. Although it is widely distributed from tropical to temperate regions, its populations are not abundant (
Based on an environmental impact assessment report, the Datan Algal Reef, Taoyuan, Taiwan was divided into two subsections, Datan G1 and Datan G2 (
Polyps from four colonies (NMMB-CR000148 to NMMB-CR000151) were used to extract DNA. DNeasy PowerSoil Kit (Qiagen, CA, USA) was used for DNA extraction, according to the manufacturer’s protocol. The primer pair COII8068XF and COIoctR was used to amplify cox2-IGR-cox1 (
The obtained sequences were edited using Geneious Prime v. 2021.2.2 (Biomatters, New Zealand) aligned to data from
The following key used to identify species of Erythropodium is based on the original descriptions of E. caribaeorum, E. hicksoni, and E. salomonense (
1 | Coenenchyme thin generally < 1 mm. Polyps contractile, do not fully retract into coenenchyme | E. taoyuanensis sp. nov. |
– | Coenenchyme thick generally > 1 mm. Polyps retractile, fully retract into coenenchyme | 2 |
2 | Sclerites in the form of rod present | E. caribaeorum |
– | Sclerites in the form of rod absent | 3 |
3 | Coenenchymal sclerites are capstan-like triradiates or tetraradiates | E. hicksoni |
– | Coenenchymal sclerites are double-spheres | E. salomonense |
Subclass Octocorallia Haeckel, 1866
Order Alcyonacea Lamouroux, 1812
Family Anthothelidae Broch, 1916
Taiwan; same data as holotype; 21 Sep. 2020; NMMB-CR000150.Taiwan; same data as holotype; 21 Sep. 2020; M.-H. Lin and L.-C. Liu leg.; NMMB-CR000151.
The holotype colony is composed of upright polyps arising separately from a encrusting membrane less than 1 mm thick or a network of ribbon-like stolons. When fully extended, polyps are around 3 mm long, and the tentacles are slender with 10–13 pairs of pinnules on either side of the rachis. Polyps are contractile and cannot fully retract into the basement layer. Sclerites are mostly 6-radiate sclerites, with a few being irregular radiates. When alive, polyps are yellowish pink, and the basement layer is magenta.
(Figs
Polyps. When fully extended, the polyps may attain approximately 2.5–3.0 mm in length (Fig.
Sclerites. Sclerites are present in all parts of the holotype and evenly distributed in the coenenchyme, polyp body wall, tentacles, and pinnules. Six-radiate sclerites are the commonest type, representing more than 90% of sclerites in anthocodiae and tentacles. They are 0.032–0.068 mm in length and 0.025–0.036 mm in width with simple tubercles (Fig.
Color. In life, colors of tissue, autozooids, and cortical layer are translucent, white to yellowish, and pink to magenta, respectively. Under light microscope, sclerites are translucent, magenta, or reddish.
Variation. Paratype (NMMB-CR000149) and non-type specimens (NMNB-CR000150 and NMNB-CR000151) show variation in the density of polyps ranging 5–20/cm2. Six-radiate sclerites are the commonest type of sclerites in the examined specimens, while their sizes are varied not only in different parts of a colony but also differ from what was observed in the holotype and across the specimens. The length and width of 6-radiate sclerites in the examined specimens is 0.020–0.068 mm and 0.020–0.053 mm, respectively, in polyp tissue; 0.024–0.098 mm and 0.018–0.070 mm, respectively, in polyp wall; and 0.022–0.118 mm and 0.026–0.075 mm, respectively, in cortex (Figs
When comparing the morphology of E. taoyuanensis sp. nov. to the other three Erythropodium species, basal membrane, pinnule arrangement, retractile or contractile ability of polyps, and shape and size of sclerites (Table
Species name | Diagnostic traits | ||||
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Colony | Coenenchyme | Polyp | Sclerite | References | |
Erythropodium caribaeorum | Encrusting, membranous carpet-like colony | Thick cortical layer, ~3 mm | Retractile polyps with elongated pinnules arragned in a single pair of rows | Dominant 6-radiate sclerites and irregular radiate scleirtes |
|
Erythropodium hicksoni | Membranous colony | Thick cortical layer, ~3 mm | Retractile polyps with 9 pairs of pinnules per tentacle | Triradiates, quadriradiates, flattened rods, and spindles |
|
Erythropodium salomonense | Encrusting form | Thick cortical layer, 1.5–2 mm | Retractile polyps | Spindles, double spheres, irregular sclerites |
|
Erythropodium taoyuanensis | Encrusting, membranous carpet-like colony | Think cortical layer, generally < 1 mm | Contractile polyps with 10–13 pairs of pinnules per tentacle | Dominant 6-radiate sclerites and derivatives of radiates | Present study |
According to
The specific name taoyuanensis alludes to the city’s name, Taoyuan, where the specimens were collected.
The Datan G2 in Datan Algal Reef, Taoyuan, Taiwan, is the only location where this species is known; it has a biodiverse coralline algal reef. Erythropodium taoyuanensis sp. nov. is one of the dominant sessile organisms encrusting the rocks at this location and is generally restricted to near the low tidal line, and it may be exposed to the air during the spring low tide.
Sequencing nuclear 28S rDNA, and mitochondrial cox2-IGR-cox1 and msh1 resulted in 784, 777, and 585 bps, respectively, yielding a concatenated alignment of 2542 bps containing 1641 phylogenetically informative sites. All four E. taoyuanensis sp. nov. specimens in this collection had identical genotypes at the sequenced regions. The genetic distances (uncorrected p) between the specimens from the Datan Algal Reef and E. caribaeorum are 6.2% at msh1, 3.7% cox2-IGR-cox1, and 4.5% at 28S. As has been demonstrated previously based on analyses of similar datasets (
Phylogenetic relationship reconstruction (2543 nt of concatenated msh1, cox2-IGR-cox1, 28S rDNA) of the Holaxonia–Alcyoniina clade of Octocorallia. Solid circles at nodes indicate strong support from both maximum-likelihood (bootstrap value > 70%) and Bayesian inference (posterior probability > 0.95); split circles indicate strong support from one analysis only (left half solid: supported by maximum-likelihood; right half solid: supported by Bayesian analyses).
Erythropodium taoyuanensis sp. nov. has only been discovered in the tidal pools at Datan G2 of the Datan Algal Reef. The tidal pool is periodically exposed to air and experiences variation in salinity, dissolved oxygen content, and temperature. Therefore, it is not a typical habitat for octocorals, and only a couple of species of Sinularia or Asterospicularia of Xeniidae have been observed in Taiwanese reefs (
Morphologically, the specimens (NMMB-CR000148 to NMM-CR000151) collected from the Datan Algal Reef possessed the diagnostic feature of Erythropodium, such as thin, firm colony expansions on rocks and sclerites that are all derivatives of 6-radiate sclerites (
We thank M.-H. Lin, L.-C. Liu, and E.-J. Lin for assistance with collection of samples and fieldwork. P.-H. Chen assisted with DNA sequencing. Financial support was provided by the Taiwanese Ministry of Science and Technology (MOST 109-2116-M-110-001-MY3).
Table S1
Data type: xlsx file
Explanation note: Sequnece used for phyloenetic reconstruction and their respective GenBank Accession numbers, according to McFadden & Ofwegen (2012).