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ISSN : 1226-9999(Print)
ISSN : 2287-7851(Online)
Korean J. Environ. Biol. Vol.44 No.2 pp.131-149
DOI : https://doi.org/10.11626/KJEB.2026.44.2.131

Seven marine gastropods newly recorded from Korea with morphological diagnoses and DNA barcode data

Dae-Wui Jung*, Andrew Eunhak Lee, Jong Guk Kim1, Young Ho Koh2, Won-Gi Min3
Korea Marine-Bio Laboratory, Daejeon 34130, Republic of Korea
1Honam National Institute of Biological Resources, Mokpo 58762, Republic of Korea
2Department of Taxonomy and Systematics, National Marine Biodiversity Institute of Korea, Seocheon 33662, Republic of Korea
3East Sea Research Institute, Korea Institute of Ocean Science and Technology, Uljin 36315, Republic of Korea
*Corresponding author Dae-Wui Jung nudibranchlab@gmail.com

Contribution to Environmental Biology


▪ The present study improves current knowledge of marine gastropod diversity in Korean waters by documenting seven previously unrecorded species based on morphological characteristics and mitochondrial COI barcode analyses.


▪ These records provide useful baseline data for future monitoring of marine biodiversity and regional faunal changes in the northwestern Pacific.


13 April 2026 22 June 2026 24 June 2026

Abstract


This study reports seven new records of marine gastropod species from Korean waters: Marsenina uchidai, Littoraria sinensis, Conus litteratus, Pleurobranchus forskalii, Placida dendritica, Placida kevinleei, and Thuridilla lineolata. Notably, this marks the first documentation of the genus Marsenina in Korea. Specimens were collected from various locations along the Korean coast, including Goseong and Yangyang (Gangwon-do), Dokdo, Bito Island (Sacheon, Gyeongsangnam-do), and Jeju Island, between February 2025 and March 2026. Each species identification was based on diagnostic morphological characters and supported by photographs of living individuals or preserved specimens. Uncorrected p-distance analyses and maximum-likelihood (ML) phylogenetic reconstructions, using COI sequences, confirmed the taxonomic identities of the specimens. Among the species studied, Conus literatus and Placida dendritica showed significantly higher intraspecific genetic divergences compared to the other taxa, indicating a need for further taxonomic and population-level research. These findings enrich the existing inventory of marine gastropod biodiversity in Korean waters and offer foundational data for future taxonomic and biogeographic studies.


Conus litteratus , Littoraria sinensis , Marsenina uchidai , Pleurobranchus forskalii , Sacoglossa

초록

    1. INTRODUCTION

    Marine gastropods represent one of the most diverse groups within Mollusca and inhabit a wide range of marine environments, from intertidal zones to deep-sea habitats, including extreme habitats such as hydrothermal vents (Bouchet et al. 2002;Ramirez-Llodra et al. 2007). However, species identification in marine gastropods is often challenging due to high morphological variability and the presence of cryptic species and species complexes (Korshunova et al. 2021;Shin and Allmon 2023). Accordingly, accurate species identification is essential for understanding biodiversity, biogeographic patterns, and conservation. Therefore, careful morphological documentation, together with the accumulation of publicly available DNA barcode reference sequences linked to voucher specimens, is increasingly important for documenting local biodiversity and improving the reliability of future species identifications (Bucklin et al. 2011).

    The Korean Peninsula lies at the boundary between temperate and subtropical biogeographic regions and supports a diverse marine molluscan fauna (Lee and Min 2002;Noseworthy et al. 2007;Lutaenko and Noseworthy 2014). Recent faunal surveys have reported an increasing number of previously unrecorded gastropod species from Korean waters, including subtropical and tropical taxa (Jung and Lee 2024;Cho et al. 2025;Jung et al. 2025;Lee et al. 2025). Such findings may reflect northward range shifts associated with ocean warming, as well as increased survey efforts (Parmesan and Yohe 2003;Poloczanska et al. 2013). The documentation of newly recorded species provides baseline data for marine biodiversity in Korea. Nevertheless, comprehensive documentation of newly recorded species remains necessary to refine the national inventory and improve our understanding of ongoing faunal changes in Korean waters.

    In this study, we report seven gastropod species newly recorded from Korean waters: Marsenina uchidai, Littoraria sinensis, Conus litteratus, Pleurobranchus forskalii, Placida dendritica, Placida kevinleei, and Thuridilla lineolata. These species were collected from several localities, including Goseong-gun and Yangyang-gun, Gangwon-do, Dokdo, Ulleung-gun, Gyeongsangbuk-do, Bito Island, Sacheon-si, Gyeongsangnam-do, and Seogwipo-si, Jeju Island (Fig. 1). We provide morphological diagnoses, in situ photographs and specimen images, and mitochondrial COI sequences deposited in GenBank to expand the DNA barcode reference library for Korean gastropods. Our findings update the known distribution of these species in the northwestern Pacific and provide an important baseline for future taxonomic, ecological, and conservation research in the region.

    2. MATERIALS AND METHODS

    Seven gastropod species were collected from Korean coastal waters between February 2025 and March 2026 (Fig. 1). Littoraria sinensis was obtained from the upper intertidal zone, approximately 2 m above the high-tide level on a rocky substrate; the other six species were collected from subtidal habitats at depths ranging from 3 to 52 m. Photographs of living animals or preserved specimens were taken using an Olympus Tough TG-7 digital camera (Olympus, Tokyo, Japan) and a Sony α7 III digital camera (Sony, Tokyo, Japan). Collected specimens were examined under a stereomicroscope (Olympus SZ61; Olympus, Tokyo, Japan). Prior to preservation, specimens were anesthetized in an 8% MgCl2 solution and subsequently fixed in 95% ethanol. All examined specimens were deposited in the Honam National Institute of Biological Resources (HNIBRIV25096–102) and Korea Marine-Bio Lab (KOMBI-KM126–131), Korea.

    Genomic DNA was extracted from foot tissue using the LaboPassTM Tissue Genomic DNA Isolation Kit Mini (Cosmogenetech, Seoul, Korea) according to the manufacturer’s instructions. Fragments of the mitochondrial cytochrome c oxidase subunit I (COI) gene were amplified using the primer set LCO1490 and HCO2198 (Folmer et al. 1994). The thermal cycling profile consisted of an initial denaturation at 95°C for 3 min, followed by 35 cycles of denaturation at 95°C for 30 s, annealing at 45–50°C for 30 s, and extension at 72°C for 1 min, with a final extension step at 72°C for 5 min. Newly obtained sequences were deposited in the GenBank database under accession numbers PZ263189–PZ263198. To assess the taxonomic identities of the examined specimens, COI sequences of congeners were retrieved from GenBank (Table 1) and aligned with the newly generated sequences using MUSCLE (Edgar 2004). Uncorrected p-distances were calculated using MEGA 12 (Kumar et al. 2024). Maximum-likelihood (ML) phylogenetic analyses were performed using IQ-TREE v2 (Nguyen et al. 2015). The best-fit nucleotide substitution model for each dataset was selected under the Bayesian Information Criterion (BIC) using ModelFinder v3.0.1 (Kalyaanamoorthy et al. 2017). Nodal support values were estimated with 1,000 ultrafast bootstrap replicates (Hoang et al. 2018).

    3. SYSTEMATIC ACCOUNTS

    Phylum Mollusca Linnaeus, 1758 연체동물문

    Class Gastropoda Cuvier, 1797 복족강

    Order Littorinimorpha Golikov and Starobogatov, 1975 총알고둥목

    Family Velutinidae Gray, 1840 배고둥붙이과

    Genus Marsenina Gray, 1850 큰배고둥붙이속(신칭)

    Type species.Oxinoe glabra Couthouy, 1838 (type by monotypy).

    Diagnosis. Hermaphroditic. Mantle with a slit or pore exposing shell and enabling mantle retraction. Foot small, smooth, and concealed beneath mantle. Radula formula n×2.1.1.1.2. (Behrens et al. 2014).

    *Marsenina uchidai (Habe, 1958) 큰배고둥붙이 (신칭) (Supplementary Table S1; Figs. 1, 2A–C, 3)

    Lamellaria uchidai Habe, 1958: 14, 15, Pl. 1, Fig. 11.

    Marsenina uchidai: Gulbin and Golikov, 2000: 146, Fig. 6.

    Type locality. Akkeshi Bay, Hokkaido, Japan (Habe 1958).

    Distribution. Northwest Pacific: Russia, Korea, and Japan (Habe 1958;Gulbin and Golikov 2000; this study).

    Materials examined. 2 individuals, Munamjin-ri, Jugwang-myeon, Goseong-gun, Gangwon-do (Fig. 1), 31 Jan 2026, DW Jung and AE Lee (HNIBRIV25096, KOMBI-KM127).

    Measurement. Body length 9 mm; shell height 7 mm; shell width 5 mm.

    Diagnosis. Mantle opaque white, broad, entirely covering the foot, metapodium occasionally exposed (Fig. 2A). Anterior and right lateral mantle folds forming siphons. Mantle surface with minute black dots and sponge-like pores. Rhinophores digitiform, slender, and smooth. Shell oval, translucent white, fragile (Fig. 2B). Protoconch small. Spire very low, composed of three convex whorls (Fig. 2C). Body whorl greatly expanded, with a rounded and descending shoulder. Shell surface bearing indistinct growth lines with a thin periostracum. Aperture oval and wide. Outer lip thin. Columellar margin broadly curved and weakly thickened.

    GenBank Accession No. PZ263189.

    Remarks. The specimens examined in this study show no significant differences from the original description and subsequent reports (Habe 1958;Gulbin and Golikov 2000). Both the type specimen and the present material possess three whorls, whereas Gulbin and Golikov (2000) reported 3.5 whorls. Habitat records indicate that the type material (Habe 1958) originated from shallow eelgrass meadows, whereas Gulbin and Golikov (2000) documented the species from the intertidal zone to depths of 150 m on rocky and sandy substrates. The present specimens were collected from rocky substrates at approximately 30 m depth.

    The present study provides a COI sequence for Marsenina uchidai and deposits it in GenBank for the first time. In the maximum-likelihood phylogenetic tree, the Korean specimen formed a distinct lineage within the genus Marsenina and was recovered as the sister taxon to M. pax (Fig. 3). The minimum interspecific genetic distance was 9.47% from M. rhombica (Supplementary Table S1). Although no conspecific COI sequence was previously available for direct comparison, the phylogenetic placement of the Korean specimen within the genus Marsenina and its clear genetic divergence from congeners support its morphological identification as M. uchidai.

    Family Littorinidae Children 1834 총알고둥과

    Genus Littoraria Gray 1833 얼룩총알고둥속

    *Littoraria sinensis (Philippi, 1847) 뼾족꼬마총알고둥(신칭) (Table 2, Supplementary Table S2; Figs. 1, 2D, 4)

    Litorina sinensis Philippi, 1847: 16–17, Pl. 6, Fig. 23.

    Litorina strigata Lischke, 1871: 73, Pl. 5, Fig. 2.

    Littorina adonis Yokoyama, 1927: 451, Pl. 51, Fig. 8.

    Littoraria sinensis: Lin et al. 2025: 31, Fig. 3G–Q.

    Type locality. China (Philippi 1847).

    Distribution. Northwest Pacific: China, Korea, and Japan (Lin et al. 2025; this study).

    Materials examined. 2 individuals, Bito-ri, Seopo-myeon, Sacheon-si, Gyeongsangnam-do (34°58ʹ54ʺN, 127°57ʹ57ʺE; Fig. 1), 15 Apr 2025, DW Jung and H Oh (HNIBRIV25097, KOMBI-KM126).

    Measurement. Shell height 12–13 mm; shell width 9 mm.

    Diagnosis. Shell small, yellowish ivory overall (Fig. 2D). Apex pointed. Spire high; each whorl rounded, not angulate. Suture impressed, brown. Shoulder weak. Body whorl non-carinate, with short brown dashes arranged on the spiral ribs and white dashes interspersed between brown dashes. Penultimate whorl pale purplish brown. Outer lip thin. Inner lip glossy white, without continuation of the body-whorl pattern. Aperture oval, ivory, with the external pattern visible through the shell.

    GenBank Accession No. PZ263190.

    Remarks. The Korean specimens were collected from the upper intertidal zone on rocky substrates, approximately 2 m above the high-tide level, consistent with the ecology of Littoraria sinensis as a high-shore littorinid inhabiting rocky intertidal environments subject to marked thermal fluctuation in the upper shore (Li et al. 2022;Wang and Wang 2023).

    The Korean specimens agree well with the original description and subsequent accounts of Littoraria sinensis, particularly in their small shell size, yellowish-ivory coloration, rounded and non-angulate whorls, non-carinate body whorl, brown dashes, and oval aperture.

    In Korea, Littoraria sinensis can be compared with three previously recorded congeners, L. articulata (Philippi), L. intermedia (Philippi), and L. scabra (Linnaeus), which share generally similar shell morphology. However, L. sinensis can be distinguished from these species by a combination of shell characters, particularly spire height, whorl profile, shell form, spiral sculpture, and color pattern (Table 2).

    In the maximum-likelihood phylogenetic tree, the Korean specimen clustered with previously reported sequences of Littoraria sinensis and formed a well-supported monophyletic clade (bootstrap=100) (Fig. 4). The intraspecific genetic divergence of L. sinensis ranged from 0 to 0.63%, whereas the minimum interspecific divergence was 8.39% from its closest relative, L. flammea (Supplementary Table S2). These molecular results are consistent with the morphological identification of the Korean specimen and further support its assignment to L. sinensis.

    Order Neogastropoda Wenz, 1938 신복족목

    Family Conidae Fleming, 1822 청자고둥과

    Genus Conus Linnaeus, 1758 청자고둥속

    *Conus litteratus Linnaeus, 1758 글자무니청자고둥(신칭) (Supplementary Table S3; Figs. 1, 2E, 5)

    Conus litteratus Linnaeus, 1758: 712

    Conus arabicus Lamarck, 1810: 40, Pl. 323, Figs. 1, 4, Pl. 324, Fig. 5.

    Conus grueneri Reeve, 1843: Pl. 43, Fig. 231.

    Cucullus pardus Röding, 1798: 41.

    Type locality. Asiatic Ocean (verbatim; Linnaeus 1758).

    Distribution. Indo-West Pacific: Seychelles, India, Thailand, China, Taiwan, the Philippines, Indonesia, Korea, and Japan (Okutani 2000;Lee and Chao 2004;Venkitesan et al. 2019;Wells et al. 2021; this study).

    Material examined. 1 individual, Bomok-dong, Seogwipo-si, Jeju-do (33°13ʹ54ʺN, 126°35ʹ52ʺE; Fig. 1), 14 Feb 2025, DW Jung (HNIBRIV25098).

    Measurement. Shell height 40 mm; shell width 18 mm.

    Diagnosis. Shell conical, white, moderately solid (Fig. 2E). Spire low, weakly elevated. Apex blunt. Shoulder broad, angulate, without nodules. Body whorl smooth, bearing numerous brown spots arranged in about 18–20 spiral rows, spots on shoulder dense and partially confluent. Three pale light-brown spiral bands present on spiral rows 1–4, 6–8, and 11–13. Aperture narrow, interior white, non-glossy; both inner and outer lips concolorous with body whorl. Brown spots of body whorl visible through the aperture. Anterior end dark brown.

    GenBank Accession No. PZ263191.

    Remarks. A single specimen was collected from a rocky substrate at a depth of 52 m at Munseom, Jeju Island. The examined specimen matches the original description of Conus litteratus and is consistent with subsequent accounts in having a white, conical shell bearing brown spots and pale light-brown spiral bands.

    Within the genus, C. litteratus resembles C. eburneus Hwass, C. imperialis Linnaeus, C. leopardus (Röding), and C. pulicarius Hwass in having a whitish shell with numerous brown spots on the body whorl. It is distinguished from C. eburneus by its slenderer shell and a more distinctly angulate shoulder. Conus imperialis has prominently tuberculate shoulders, whereas C. litteratus has smooth shoulders without nodules. It is further distinguished from C. leopardus by the presence of pale light-brown spiral bands and a patterned inner lip margin. It differs from C. pulicarius in having an angulate shoulder lacking nodules, whereas C. pulicarius has a rounded shoulder with tubercles and more irregularly distributed brown markings.

    COI sequences of 21 Conus litteratus specimens, including the specimen examined in the present study and sequences retrieved from GenBank, showed an intraspecific genetic divergence of 0–8.16% (Supplementary Table S3). The highest divergence (8.16%) was observed between a specimen from India (ON942254) and a specimen from Papua New Guinea (PV713814). In the maximum-likelihood phylogenetic tree, specimens identified as C. litteratus formed two distinct clades corresponding to the Indian Ocean and Pacific Ocean populations (Fig. 5). The Korean specimen was recovered within the Pacific Ocean lineage and clustered with specimens from China, Papua New Guinea, the Philippines, and Vanuatu. These results are consistent with those of Ameri et al. (2023), who recovered two well-supported lineages of C. litteratus from the Indian and Pacific Oceans and suggested that their divergence was associated with the Sunda Shelf biogeographic barrier. The inter-lineage genetic divergence reported by Ameri et al. (2023) ranged from 7.4–7.6%, which is comparable to the divergence observed in the present study (7.34–8.16%). However, neither Ameri et al. (2023) nor the present study detected any consistent morphological differences between the two lineages. Although the observed genetic divergence suggests substantial genetic structuring within C. litteratus, additional sampling and integrative taxonomic studies incorporating morphological and molecular data are required to determine whether these lineages represent distinct species.

    Order Pleurobranchida 군소붙이목

    Family Pleurobranchidae Gray, 1827 군소붙이과

    Genus Pleurobranchus Cuvier, 1804 군소붙이속

    *Pleurobranchus forskalii Rüppell and Leuckart, 1828 고리무니군소붙이 (Supplementary Table S4; Figs. 1, 6A, 7)

    Pleurobranchus forskalii Rüppell and Leuckart, 1828: 18–20, Pl. 5, Fig. 2a, b.

    Pleurobranchus perrieri Vayssière, 1896: 126–128, Pl. 4, Figs. 2–4.

    Oscanius semperi Vayssière, 1896: 134–135, Pl. 4, Fig. 1.

    Susania ceylonica White, 1948: Fig. 2 (cited from Goodheart et al. 2015).

    Susania karachiensis White, 1946: 55–56, Figs. 8–10, Pl. 5, Fig. 7 (cited from Goodheart et al. 2015).

    Type locality. Massawa, Eritrea (Red Sea; Rüppell and Leuckart 1828).

    Distribution. Indo-West Pacific: Tanzania, Red Sea, Indonesia, the Philippines, Korea, Japan, Papua New Guinea, Australia; Central Pacific: Fiji, the USA (Guam) (Goodheart et al. 2015;Gosliner et al. 2018; this study).

    Material examined. 1 individual, Dokdo, Ulleung-eup, Ulleung-gun, Gyeongsangbuk-do (Fig. 1), 03 Sep 2025, JG Kim and WG Min (HNIBRIV25099).

    Measurement. Body length 37 mm (preserved specimen).

    Diagnosis. Body ovate and convex. Mantle broad, extending over the foot. Dorsum bearing large, rounded to subquadrate low nodules; densely covered with numerous small tubercles (Fig. 6A). Large nodules bright orange to brown, their margins outlined with a white hue. Mantle margin slightly undulated, with a prominent lobe at posterior end. Mantle margin brown in areas lacking large nodules or tubercles. Rhinophores enrolled, opaque brown, with light brown and white specks. Oral veil opaque brown, trapezoidal. Metapodium short, occasionally visible beyond the posterior end of the mantle. Gill rachis and axes tuberculate.

    GenBank Accession No. PZ263192.

    Remarks. This species reaches a maximum body length of 300 mm (Gosliner et al. 2008). The background color ranges from light orange to dark red or black (Gosliner et al. 2018). Variation in pattern is sometimes observed, with the large nodules lacking distinct white outlines in some specimens, and the tips of the oral tentacle are white in juveniles (Goodheart et al. 2015). The diagnostic characters observed in a single specimen from Korea correspond to the ranges reported in previous records (Rüppell and Leuckart 1828;Vayssière 1896;Gosliner et al. 2008, 2018;Goodheart et al. 2015).

    Based on the shape and size of dorsal tubercles, Pleurobranchus forskalii can be distinguished from other Pleurobranchus species previously reported from Korea: P. mamillatus Quoy and Gaimard, P. peronii Cuvier, and P. weberi (Bergh). The dorsal nodules of P. forskalii are markedly lower than in P. mamillatus. In contrast to P. peronii, which has a simple tuberculate mantle, P. forskalii bears small tubercles within rounded or subquadrate nodules. Unlike P. weberi, in which a circular pattern may be found within another circular pattern, P. forskalii does not exhibit secondary circular patterns within each low nodule.

    A comparison of COI sequences from 11 specimens of Pleurobranchus forskalii, including the specimen examined in the present study and sequences retrieved from GenBank, revealed an intraspecific genetic divergence of 0–1.37%. The minimum interspecific divergence was 14.78% from P. hilli (Supplementary Table S4). In the maximum-likelihood phylogenetic tree, the Korean specimen clustered with other P. forskalii sequences with strong support (bootstrap=99) and formed a well-supported monophyletic clade distinct from other congeners (Fig. 7). These molecular results are consistent with the morphological identification of the Korean specimen and further support its assignment to P. forskalii.

    Superorder Sacoglossa 낭설상목

    Family Limapontiidae Gray, 1847 꼭지갯민숙붙이과

    Genus Placida Trinchese, 1876 쵛쵛꼭지갯민숙이붙이속

    *Placida dendritica (Alder and Hancock, 1843) 초록양갯민숙이붙이(신칭) (Supplementary Table S5; Figs. 1, 6B–C, 8)

    Calliopaea dendritica Alder and Hancock, 1843: 233.

    Hermaea brevicornis Costa, 1867: 37, Pl. II, Fig. 6.

    Hermaea dendritica Baba, 1955: 41, Pl. 3, Fig. 9, Text-fig. 9.

    Hermaea lutescens Costa, 1866: 79, Pl. III, Fig. 5.

    Hermaea orbicularis Costa, 1866: 79–80, Pl. III, Fig. 6.

    Hermaea ornata MacFarland, 1966: 38–42, Pl. 4. Fig. 3; Pl. 10, Figs. 1–5; Pl. 30, Figs. 11, 12.

    Hermaea venosa Lovén, 1844: 50.

    Placida dendritica: Jensen, 1993: 246–247, Fig. 34; Okutani 2000: 763.

    Type locality. Torbay, Devon, England, United Kingdom (Alder and Hancock 1843).

    Distribution. North Atlantic: Norway to the Mediterranean Sea, Caribbean Sea; Northwest Pacific: Korea and Japan (Okutani 2000; this study).

    Materials examined. 6 individuals, Namae-ri, Hyun-nam-myeon, Yangyang-gun, Gangwon-do (Fig. 1), 22 Mar 2026, AE Lee, KH Kim, and JW Jung (HNIBRIV25102; KOMBI-KM128, 129).

    Measurement. Body length 1–1.5 mm (preserved specimens).

    Diagnosis. Body elongate and slender, with a translucent white ground color (Fig. 6B). Rhinophores enrolled, with multiple green longitudinal veins or pigments visible internally, extending from rhinophores along dorsum to metapodium. Dorsum covered with numerous cerata, conical or digitiform; digestive gland appearing as green and white bead-like masses visible through ceratal wall (Fig. 6C). Visceral mass occupied by green digestive gland, with opaque white masses irregularly and sparsely distributed. Each ceras with a blunt tip, predominantly opaque white. Area surrounding eyespots lacking green veins or pigment. Oral tentacles short and blunt. Foot narrow, foot corner slightly expanded anteriorly around head; metapodium short and pointed.

    GenBank Accession Nos. PZ263193 and PZ263194.

    Remarks. The specimens examined from Korean waters agree well with previous descriptions of Placida dendritica in having a translucent body and distinctive green digestive gland visible through the cerata and rhinophores (Alder and Hancock 1843;Okutani 2000;Jensen 2007). This species can be readily distinguished from other congeners in Korea by the presence of a translucent body coloration, cerata containing green and white digestive gland, and multiple internally visible green veins or pigments forming a dendritic pattern extending from the rhinophores to the body.

    Although only 6 specimens were collected on the day of sampling, approximately 50 individuals were observed on Codium hubbsii Dawson, and a single individual was found on Undaria pinnatifida (Harvey) Suringar.

    Placida dendritica has been regarded as a potential species complex because of its broad geographic distribution, although its taxonomic boundaries remain unclear (McCarthy et al. 2019). A comparison of COI sequences from 28 specimens of P. dendritica, including the specimens examined in the present study and sequences retrieved from GenBank, revealed an intraspecific genetic divergence of 0–24.67% (Supplementary Table S5). In the maximum-likelihood phylogenetic tree, all specimens identified as P. dendritica formed a well-supported clade (bootstrap=99), but were divided into two distinct subclades (Fig. 8). One subclade consisted of specimens from the northwestern Pacific, including Korea, China, Japan, and the Russian Far East, whereas the other comprised specimens from the North Atlantic and eastern Pacific regions, including Spain, the United Kingdom, the White and Barents seas of Russia, Canada, and the United States. The genetic divergence between these two geographic lineages ranged from 10.32% to 20.77%, whereas specimens from the northwestern Pacific lineage showed low divergence (0–1.08%). These results support the hypothesis that P. dendritica may represent a species complex containing cryptic diversity, although additional sampling and integrative taxonomic analyses are required to clarify its taxonomic status.

    *Placida kevinleei McCarthy, Krug and Valdés, 2017 노랑눈이갯민숙이붙이(신칭) (Supplementary Table S5; Figs. 1, 6D–E, 8)

    Placida kevinleei McCarthy et al. 2019: 366–367, Figs. 1e, 3a, 4c, 4d, 8; Chow et al. 2022: 28, Fig. 10J.

    Type locality. Okinawa, Japan (McCarthy et al. 2019).

    Distribution. Indo-West Pacific: China (Hong Kong), Korea, Japan, and Indonesia; Central Pacific: the USA (Hawaii) (McCarthy et al. 2019;Chow et al. 2022; this study).

    Materials examined. 3 individuals, Seogwi-dong, Seogwipo-si, Jeju-do (33°13ʹ39ʺN, 126°33ʹ57ʺE; Fig. 1), 30 Sep 2025, DW Jung (HNIBRIV25100; KOMBI-KM130, 131).

    Measurement. Body length 1–3 mm (preserved specimens).

    Diagnosis. Body elongate, ground color yellow (Fig. 6D). Rhinophores enrolled, predominantly black with posterior white stripe extending from base to about mid-length (Fig. 6E). Yellow patches present around eyespots. Dorsum densely covered with numerous cerata. Cerata cylindrical with pointed apices, bicolored with proximal half yellow and distal half black. Oral tentacles black. Foot yellow, anterior foot corners slightly swollen, metapodium pointed.

    GenBank Accession Nos. PZ263195–PZ263197.

    Remarks. The Korean specimens agree well with the original description of Placida kevinleei, particularly in the yellow ground coloration, black rhinophores with a posterior white stripe, yellow patches around the eyespots, and bicolored cerata with yellow proximal halves and black distal halves (McCarthy et al. 2019). This species resembles other members of the Placida cremoniana species complex, but is distinguished by the unique combination of the extent of the white stripe along the rhinophores and the presence of yellow patches around the eyespots. Placida kevinleei is characterized by a white patch extending from the eyespots along the rhinophores to approximately half their length and by the absence of a yellow linear pattern extending posteriorly from the eyespots along the lateral side of the body (McCarthy et al. 2019).

    A comparison of COI sequences from four specimens of Placida kevinleei, including the three specimens examined in the present study and one sequence retrieved from GenBank, revealed an intraspecific genetic divergence of 0–2.41%. The minimum interspecific divergence was 20.92% from P. brookae (Supplementary Table S5). In the maximum-likelihood phylogenetic tree, all P. kevinleei specimens formed a well-supported monophyletic clade (bootstrap=85) that was clearly separated from other congeners (Fig. 8). The Korean specimens clustered with the previously reported sequence of P. kevinleei with strong support (bootstrap=100). These molecular results are consistent with the morphological identification of the Korean specimens and further support their assignment to P. kevinleei.

    Family Plakobranchidae Gray, 1840 날씬이갯민숙붙이과

    Genus Thuridilla Bergh, 1872 다색갯민숙이붙이속

    *Thuridilla lineolata (Bergh, 1905) 형광파랑갯민숙이붙이(신칭) (Supplementary Table S6; Figs. 1, 6F, 9)

    Elysia lineolata Bergh, 1905: 85–86, Pl. 13, Figs. 25–26.

    Thuridilla lineolata: Jensen, 2007: 278; Martín-Hervás et al. 2025: Table 2.

    Type locality. Selayar Islands, South Sulawesi, Indonesia (Bergh 1905).

    Distribution. Indo-West Pacific: Indonesia, the Philippines, Korea, and Japan (Gosliner et al. 2018;Martín-Hervás et al. 2025; this study).

    Material examined. 1 individual, Seogwi-dong, Seogwipo-si, Jeju-do (33°13ʹ39ʺN, 126°33ʹ57ʺE; Fig. 1), 30 Sep 2025, DW Jung (HNIBRIV25101).

    Measurement. Body length 4 mm (preserved specimen).

    Diagnosis. Body elongate. Ground color bright sky blue (Fig. 6F). Rhinophores enrolled; distal two-fifths orange, with a thin black ring below the orange portion; a thin black line present near rhinophoral base. Parapodia narrow; margin with a broad orange band bordered internally by a thin black line, with orange and black lines encircling bright sky blue ground color. Inner surface of parapodia with coloration identical to outer surface. Anterior margin of foot with a thick orange band followed posteriorly by a thin black line and a bright sky-blue area; posterior part of foot tinged with orange.

    GenBank Accession No. PZ263198.

    Remarks. The Korean specimen agrees well with previous descriptions of Thuridilla lineolata in having a bright sky-blue ground coloration and a distinct orange marginal band along the parapodia. This species resembles T. coerulea (Kelaart) and T. undula Gosliner in possessing a bright sky blue body color combined with an orange parapodial marginal band. However, T. lineolata is distinguished from T. coerulea by the orange tips of the rhinophores, which are black in T. coerulea. It also differs from T. undula in the shape of the parapodial marginal band, which is straight or only slightly curved in T. lineolata, whereas it is distinctly undulating in T. undula. The combination of the bright sky-blue ground coloration, orange rhinophoral tips, and the non-undulating orange parapodial margin clearly distinguishes T. lineolata from its congeners.

    A comparison of COI sequences from three specimens of Thuridilla lineolata, including the specimen examined in the present study and sequences retrieved from GenBank, revealed an intraspecific genetic divergence of 0–0.42%. The minimum interspecific divergence was 8.16% from T. ratna (Supplementary Table S6). In the maximum-likelihood phylogenetic tree, all T. lineolata specimens formed a well-supported clade (bootstrap=100) (Fig. 9). These molecular results are consistent with the morphological identification of the Korean specimen.

    SUPPLEMENTARY MATERIALS

    Supplementary materials associated with this article can be found, in the online version, at https://doi.org/10.11626/KJEB.2026.44.2.131.

    CRediT authorship contribution statement

    DW Jung: Conceptualization, Specimen collection, Writing-Original draft. AE Lee: Specimen collection, Visualization, Writing-Original draft. JG Kim: Specimen collection, Writing-Review and editing, Supervision. YH Koh: Specimen collection, Writing-Review and editing. WG Min: Specimen collection, Logistics support, Visualization.

    Declaration of Competing Interest

    The authors declare no conflicts of interest.

    ACKNOWLEDGMENTS

    We sincerely thank Hyunmin Oh for his valuable assistance with specimen collection at Bito Island, Sacheon, Korea. This work was supported by a grant from the Honam National Institute of Biological Resources (HNIBR), funded by the Ministry of Environment (MOE) of the Republic of Korea (HNIBR2026-A-1-05).

    Figure

    KJEB-44-2-131_F1.jpg

    Collection localities of the species recorded in the present study in Korean waters. The red star indicates Marsenina uchidai; orange star, Littoraria sinensis; yellow-green star, Conus litteratus; green star, Pleurobranchus forskalii; blue star, Placida dendritica; purple star, Placida kevinleei; and black star, Thuridilla lineolata.

    KJEB-44-2-131_F2.jpg

    Photographs of examined gastropod specimens (1). A. Dorsal view of the living animal of Marsenina uchidai; B. Dorso-lateral view of the shell of Marsenina uchidai; C. Dorsal view of the shell of Marsenina uchidai; D. Ventral (left) and dorsal (right) views of Littoraria sinensis; E. Ventral (left) and dorsal (right) views of Conus litteratus. Scale bars=5 mm.

    KJEB-44-2-131_F3.jpg

    Maximum-likelihood (ML) phylogenetic tree of species of Marsenina based on COI sequences. Coriocella herberti was designated as the outgroup. The sequence obtained in the present study is indicated by gray shading. GenBank accession numbers are provided after species names. Numbers at nodes indicate ultrafast bootstrap support values; only values ≥75% are shown. The substitution model used for tree reconstruction was TVM+F+G4.

    KJEB-44-2-131_F4.jpg

    Maximum-likelihood (ML) phylogenetic tree of selected species of Littoraria based on COI sequences. Melarhaphe neritoides was designated as the outgroup. The sequence obtained in the present study is indicated by gray shading. GenBank accession numbers are provided after species names. Numbers at nodes indicate ultrafast bootstrap support values; only values ≥75% are shown. The substitution model used for tree reconstruction was TIM2+R2+F.

    KJEB-44-2-131_F5.jpg

    Maximum-likelihood (ML) phylogenetic tree of selected species of Conus based on COI sequences. Californiconus californicus was designated as the outgroup. The sequence obtained in the present study is indicated by gray shading. GenBank accession numbers are provided after species names. Numbers at nodes indicate ultrafast bootstrap support values; only values ≥75% are shown. The substitution model used for tree reconstruction was TIM3+R2+F.

    KJEB-44-2-131_F6.jpg

    Photographs of examined gastropod specimens (2). A. Dorso-lateral view of the living animal of Pleurobranchus forskalii; B. Dorso-lateral view of the living animal of Placida dendritica; C. Cerata of Placida dendritica; D. Dorsal view of the living animal of Placida kevinleei; E. White stripe on the rhinophores and yellow patches around the eyespots of Placida kevinleei; F. Dorsal view of the living animal of Thuridilla lineolata.

    KJEB-44-2-131_F7.jpg

    Maximum-likelihood (ML) phylogenetic tree of selected species of Pleurobranchus based on COI sequences. Boreoberthella chacei was designated as the outgroup. The sequence obtained in the present study is indicated by gray shading. GenBank accession numbers are provided after species names. Numbers at nodes indicate ultrafast bootstrap support values; only values ≥75% are shown. The substitution model used for tree reconstruction was TPM3u+I+F.

    KJEB-44-2-131_F8.jpg

    Maximum-likelihood (ML) phylogenetic tree of selected species of Placida based on COI sequences. Sacoproteus nishae was designated as the outgroup. Sequences obtained in the present study are indicated by gray shading. GenBank accession numbers are provided after species names. Numbers at nodes indicate ultrafast bootstrap support values; only values ≥75% are shown. The substitution model used for tree reconstruction was TPM3u+I+G4+F.

    KJEB-44-2-131_F9.jpg

    Maximum-likelihood (ML) phylogenetic tree of selected species of Thuridilla based on COI sequences. Elysia chlorotica was designated as the outgroup. The sequence obtained in the present study is indicated by gray shading. GenBank accession numbers are provided after species names. Numbers at nodes indicate ultrafast bootstrap support values; only values ≥75% are shown. The substitution model used for tree reconstruction was TPM3u+I+G4+F.

    Table

    List of specimens examined in the present study, with collection localities, voucher numbers, and GenBank accession numbers for COI sequences

    Comparison of diagnostic shell characters among Littoraria sinensis, L. articulata, L. intermedia, and L. scabra

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    Vol. 40 No. 4 (2022.12)

    Journal Abbreviation 'Korean J. Environ. Biol.'
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