Biodiversity Data Journal :
Taxonomy & Inventories
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Corresponding author: Gi-Sik Min (mingisik@inha.ac.kr)
Academic editor: Wagner Magalhães
Received: 12 Jun 2024 | Accepted: 27 Aug 2024 | Published: 16 Oct 2024
© 2024 Ha-Eun Lee, Geon Hyeok Lee, Gi-Sik Min
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:
Lee H-E, Lee GH, Min G-S (2024) A new species of Thoracophelia (Annelida, Opheliidae) from the Yellow Sea of South Korea. Biodiversity Data Journal 12: e129526. https://doi.org/10.3897/BDJ.12.e129526
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Thoracophelia Ehlers, 1897 is a genus of Opheliidae characterised by the body divided into three distinct regions, modified parapodia in chaetiger 10 and a ventral groove restricted to the posterior half of the body. To date, 18 species have been described in the genus. Amongst them, six species have been recorded in northeast Asia.
A new species, Thoracophelia foliformis sp. nov., was discovered in the intertidal zone of the Yellow Sea, South Korea. This is the first Thoracophelia species report from the Yellow Sea. This new species is closely related to T. dillonensis (Hartman, 1938) from California and T. ezoensis Okuda, 1936 from Japan in having pectinate branchiae. However, the new species can be distinguished from the two species by the unique combination of the following characteristics: 15 pairs of wrinkled pectinate branchiae with 12–15 filaments at best development and a foliaceous mid-ventral plate in the pygidium instead of one or two thick ventral cirri. Detailed descriptions and illustrations of T. foliformis sp. nov. are provided. Sequences of the mitochondrial cytochrome c oxidase subunit I (COI), nuclear 18S ribosomal DNA (rDNA) and 28S rDNA of the new species were determined and analysed.
Opheliid, Polychaeta, taxonomy, DNA barcode
Species in the family Opheliidae Malmgren, 1867 are widely distributed worldwide, from shallow to deep seas and are mainly found in sandy sediments (
The genus Thoracophelia, erected by
To date, six species have been recorded in Northeast Asia: Thoracophelia arctica (Grube, 1866), Thoracophelia ezoensis Okuda, 1936, Thoracophelia japonica (Misaka & Sato, 2003), Thoracophelia minuta Jimi et al., 2021, Thoracophelia williamsi (Hartman, 1938) and Thoracophelia yasudai Okuda, 1934 (
In the present study, we discovered a new Thoracophelia species in the intertidal zone of the Yellow Sea. Detailed descriptions and illustrations of T. foliformis sp. nov. have been provided. Sequences of the mitochondrial cytochrome c oxidase subunit I (COI), nuclear 18S ribosomal DNA (rDNA) and 28S rDNA were determined for DNA barcoding and phylogenetic studies.
Specimens were collected from the upper intertidal zone of the Yellow Sea, South Korea during March 2021 and June 2022 (Fig.
DNA was extracted from three ethanol-preserved specimens (NIBRIV0000900977, NIBRIV0000910953 and NIBRIV0000910956) using LaboPass Tissue Mini (Cosmo GENETECH, South Korea) according to the manufacturer’s instructions. The partial sequences of COI, 18S rDNA and 28S rDNA were amplified using the following primer sets: PolyLCO/PolyHCO (
Keun-yo-jeong-get-ji-reong-yi (큰요정갯지렁이속)
Holotype complete with 38 chaetigers, 17.2 mm long, 1.6 mm wide in thoracic region and 1.3 mm wide in abdominal region. Paratypes with 37–38 chaetigers, 11.1–24.2 mm long, 1.3–2.0 mm wide. Live specimens reddish in colour and body wall transparent. The reddish colour gradually fades to yellow or cream after alcohol preservation, but can remain for a year in the case of formalin fixation.
Body distinctly divided into three regions by weak constrictions; cephalic, thoracic, and abdominal regions (Fig.
Photographs of Thoracophelia foliformis sp. nov. A paratype (NIBRIV0000910958); B, F paratype (NIBRIV0000910957); C, E paratype (NIBRIV0000910956). A–C, F live specimens. A whole body, dorsal view; B whole body with everted proboscis, ventral view; C abdominal segments, lateral view; D branchiate parapodia; E cephalic region, lateral view; F mid-ventral plate of pygidium, ventral view. Abbreviation: Abd = abdomen, AC = anal cirrus, BF = branchial filament, Br = branchiae, Ce = cephalic region, LG = lateral groove, LR = lateral ridge, Mo = mouth, MvP = mid-ventral plate, NO =nuchal organ, OOC = oocyte, Po = postchaetal lobe, Pr = prostomium, Prb = proboscis, Py = pygidium, Sp = spicule, Thx = thorax, VG = ventral groove. Scale bars: A, B = 1 mm; C, E, F = 0.5 mm; D = 100 µm.
Staining patterns and SEM images of Thoracophelia foliformis sp. nov. A–E paratype (NIBRIV0000910952); F, G paratype (NIBRIV0000910951); H–K paratype (NIBRIV0000910954). A whole body, lateral view; B circular patch at the base of branchiae; C prostomium; D dorsal pattern; E pygidium; F branchiae; G parapodia, anterior view; H pygidium, lateral view; I branchial filament; J serrated chaetae; K serration of chaeta. Abbreviation: LO = lateral organ, Ne = neuropodia, No = notopodia. Scale bars: A = 1 mm; B, C, H = 0.2 mm; D, E = 0.5 mm; F = 100 µm; G, I = 50 µm; J = 10 µm; K = 1 µm.
Branchiae pectinate, wrinkled, occurring from chaetigers 14 to 28 (Fig.
Parapodia biramous, with rounded postchaetal lobes on each noto- and neuropodia (Fig.
Chaetae distally serrated in one side (Fig.
Pygidium with about 6–8 anal cirri on each lateral side and a foliaceous mid-ventral plate, flattened, wider basally and distally tapering (Fig.
Fifteen pairs of branchiae present on chaetiger 14–28. Branchiae pectinate, wrinkled and the well-developed ones bear 12–15 finger-shaped branchial filaments. Chaetiger 10 with a pair of smooth lateral ridge. Pygidium with a foliaceous mid-ventral plate and about 6–8 anal cirri on each lateral side.
The new specific name derives from the foliaceous shape of the mid-ventral plate in the pygidium. The name is a combination of the Latin words folium (meaning ‘leaf’) and formis (meaning ‘shape’).
The new species was collected from the upper intertidal zone, which consists of sand or muddy sand, in the Yellow Sea of South Korea (Fig.
Although the number of branchial filaments in well-developed branchiae is variable (12–15), there was no variation in the number of pairs of branchiae (15 pairs) or the first branchiae-bearing chaetiger (chaetiger 14) amongst the specimens.
Female adult specimens were observed in the present study. Oocytes present in coelom cavity, with about 0.1 mm diameter, visible through the transparent body wall (Fig.
Annulations of each segment have weak line-shaped stain and the stains are thicker at mid-dorsal abdominal region (Fig.
Sequences of mitochondrial COI, nuclear 18S rDNA and 28S rDNA were obtained from the three specimens of Thoracophelia foliformis sp. nov. The intraspecific variation in 28S rDNA (849 bp) was 0.1%; however, there was no intraspecific variation in COI (657 bp) or 18S rDNA (1,684 bp). The interspecific variations between the new species and the congeners were 14.2–15.4% in COI (654 bp), 0.2–0.3% in 18S rDNA (1,750 bp) and 3.6–4.2% in 28S rDNA (873 bp) (Table
Interspecific genetic distances of three genes (COI, 18S rDNA and 28S rDNA) amongst Thoracophelia species and an outgroup species, Ophelia limacina.
Species | Interspecific genetic distance | GenBank accession No. | ||||||
COI (654 bp aligned) | 1 | 2 | 3 | 4 | 5 | |||
1 | T. foliformis sp. nov. | PP903709 | ||||||
2 | T. dillonensis | 0.154 | KC164681 | |||||
3 | T. minuta | 0.142 | 0.115 | MW429791 | ||||
4 | T. mucronata | 0.147 | 0.126 | 0.122 | KC164687 | |||
5 | T. williamsi | 0.146 | 0.091 | 0.116 | 0.116 | KC164691 | ||
6 | Ophelia limacina | 0.175 | 0.187 | 0.185 | 0.169 | 0.176 | KC164692 | |
18S rDNA (1,750 bp aligned) | 1 | 2 | 3 | 4 | 5 | 6 | ||
1 | T. foliformis sp. nov. | PP905511 | ||||||
2 | T. dillonensis | 0.003 | KF511830 | |||||
3 | T. ezoensis | 0.003 | 0.003 | HM746725 | ||||
4 | T. minuta | 0.003 | 0.003 | 0.001 | MW429485 | |||
5 | T. mucronata | 0.002 | 0.001 | 0.002 | 0.001 | KF511831 | ||
6 | T. williamsi | 0.003 | 0.001 | 0.003 | 0.003 | 0.002 | KF511832 | |
7 | Ophelia limacina | 0.006 | 0.007 | 0.005 | 0.004 | 0.006 | 0.006 | KF511829 |
28S rDNA (873 bp aligned) | 1 | 2 | 3 | 4 | 5 | 6 | ||
1 | T. foliformis sp. nov. | PP905508 | ||||||
2 | T. dillonensis | 0.037 | KF511851 | |||||
3 | T. ezoensis | 0.042 | 0.025 | HM746738 | ||||
4 | T. minuta | 0.039 | 0.026 | 0.007 | MW429484 | |||
5 | T. mucronata | 0.036 | 0.001 | 0.024 | 0.024 | KF511852 | ||
6 | T. williamsi | 0.042 | 0.005 | 0.031 | 0.031 | 0.008 | KF511854 | |
7 | Ophelia limacina | 0.067 | 0.066 | 0.075 | 0.077 | 0.067 | 0.066 | KF511850 |
Thoracophelia foliformis sp. nov. is the first Thoracophelia species described in the Yellow Sea. In possessing pectinate branchiae, Thoracophelia foliformis sp. nov. resembles Thoracophelia dillonensis (Hartman, 1938) from California and Thoracophelia ezoensis Okuda, 1936 from Japan. While most similar to T. dillonensis in having 15 pairs of branchiae, the new species is distinguished from T. dillonensis by the shape of its branchiae and pygidium. The new species has wrinkled branchiae with 12–15 filaments at best development and a foliaceous mid-ventral plate in the pygidium, whereas T. dillonensis has unwrinkled, smooth branchiae with 15–20 filaments at best development and two thick mid-ventral cirri instead of the plate. Thoracophelia ezoensis also differs from the new species as the former possesses 19 pairs of branchiae and a thick mid-ventral cirrus, whereas the latter has 15 pairs of branchiae and a foliaceous mid-ventral plate. Furthermore, the new species also differs from the two species, as the branchiae of the new species first appear on chaetiger 14, while those of the two species first appear on chaetiger 13. In Northeast Asia, six species have been reported and are clearly distinguished from the new species by the shape of the branchiae, except T. ezoensis mentioned above. Morphological differences amongst those species are mentioned in the identification keys below.
Yip-sa-gwi-Keun-yo-jeong-get-ji-reong-yi (잎사귀큰요정갯지렁이)
Key to Thoracophelia species in Northeast Asia |
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1 | Branchiae with 3 or less branchial filaments | 2 |
– | Branchiae with more than 3 branchial filaments | 3 |
2 | Branchiae simple, hemisphere-shaped | T. minuta Jimi et al., 2021 |
– | Branchiae bifid and sometimes trifid | T. williamsi (Hartman, 1938) |
3 | Branchiae dichotomously branched | 4 |
– | Branchiae not dichotomously branched | 5 |
4 | With 15 pairs of branchiae | T. yasudai Okuda, 1934 |
– | With 17 pairs of branchiae | T. arctica (Grube, 1866) |
5 | Branchiae palmatifid; Chaetiger 10 with 11 dorsal and 3 ventral conical cirri | T. japonica (Misaka & Sato, 2003) |
– | Branchiae pectinate; Chaetiger 10 with smooth lateral ridge | 6 |
6 | With 19 pairs of branchiae, first appearing on chaetiger 13 | T. ezoensis Okuda, 1936 |
– | With 15 pairs of branchiae, first appearing on chaetiger 14 | T. foliformis sp. nov. |
To date, 18 species have been described in the genus Thoracophelia. The new species is clearly distinguished from the previously-described Thoracophelia species, based on the shape of the branchiae and pygidium. In possessing pectinate branchiae, T. foliformis sp. nov. resembles T. dillonensis and T. ezoensis. However, the new species is distinguished from T. dillonensis by its wrinkled branchiae with fewer branchial filaments (12–15 vs. 15–20) at full development and a mid-ventral plate in the pygidium. Although the number of branchial filaments is a variable characteristic defined in the range, a 15.4% dissimilarity in COI sequences indicates that the new species is clearly distinguished from T. dillonensis (Table
Maximum Likelihood (ML) and Bayesian Inference (BI) analyses, based on COI and 18S+28S rDNA sequences. The numbers at nodes represent the ML bootstrap values of ≥ 50% and the BI posterior probabilities of ≥ 0.5. New species is in bold. Ophelia limacina and Polygordius lacteus were used as outgroup taxa.
In Korea, T. williamsi has been reported from Sea of Japan without description and deposition information by Song et al. (2017). The new species described in this paper is clearly distinguished from T. williamsi because the former has pectinate branchiae, while the latter possess bifid and trifid branchiae with pinnates on dorsal filaments (
Recent studies on Opheliidae using scanning electron microscopy (SEM) have revealed the presence of ciliated areas on lateral organs and branchiae and the diversity in the structure of lateral and nuchal organs, which may be reliable taxonomic characters for future phylogenetic studies (
Staining methods have been used for species identification in several annelid taxa by observing indistinct surface features or revealing specific staining patterns (
In COI, the minimum interspecific variation between the new species and congeners was 14.2% for T. minuta (Table
This study was supported by a grant from the National Institute of Biological Resources (NIBR), funded by the Ministry of Environment (MOE) of the Republic of Korea (NIBR202333201). This study was also supported by Inha University.
Maximum Likelihood (ML) and Bayesian Inference (BI) analyses, based on 18S and 28S rDNA sequences. The numbers at nodes represent the ML bootstrap values of ≥ 50% and the BI posterior probabilities of ≥ 0.5. New species is in bold. Polygordius lacteus was used as an outgroup taxon.