The Fauna of Parasitic Barnacles (Cirripedia: Rhizocephala) in Korea

© 2024 Academia Sinica, Taiwan Open Access The Fauna of Parasitic Barnacles (Cirripedia: Rhizocephala) in Korea Jibom Jung1,2 and Joong-Ki Park1,* 1Division of EcoScience, Ewha Womans University, Seoul 03760, South Korea. *Correspondence: E-mail: [email protected] (Park) 2School of Biological Sciences, Seoul National University, Seoul 08826, South Korea. E-mail: [email protected] (Jung) Received 31 August 2023 / Accepted 21 December 2023 / Published 15 March 2024 Communicated by Benny K.K. Chan Rhizocephala is a group of endoparasitic barnacles, the morphological characteristics of which are degenerated, and which has recently undergone active molecular identification. Despite several recent studies of Korean rhizocephalans, a comprehensive analysis of rhizocephalan fauna has not yet been conducted. In this study, we analyzed morphological and molecular characteristics of 64 rhizocephalan samples from 15 decapod hosts sampled across the Korean coast. We found 16 Rhizocephala species of six genera from four Rhizocephala families, i.e., Peltogasterellidae, Peltogastridae, Polyascidae, and Sacculinidae. Combining morphological examination and molecular analysis of mitochondrial cytochrome c oxidase I revealed three new species candidates, i.e., Peltogasterella sp., Peltogaster sp., and Parasacculina sp. 1, and three rhizocephalans that have expanded their distribution range to the Korean coast, i.e., Parasacculina oblonga, Sacculina angulata, and Sacculina gracilis, whose expanded their distribution range to Korean coast. A synthetic update of Korean Rhizocephala fauna including a species checklist and remarks regarding distribution and taxonomy is also presented. Key words: Rhizocephala, Cirripedia, Parasitic barnacles, Decapod hosts, Distribution pattern, Korean coast Citation: Jung J, Park JK. 2024. The fauna of parasitic barnacles (Cirripedia: Rhizocephala) in Korea. Zool Stud 63:01. doi:10.6620/ZS.2024.6301. BACKGROUND Rhizocephala is a group of parasitic barnacles that infect both the internal (endoparasitic) and external body (ectoparasitic) of crustacean hosts, mainly decapods. The organism has a complicated life cycles, beginning with a planktonic larval stage, followed by an internal parasitic stage, and concluding with an external reproductive stage (Høeg 1992). In contrast to other crustacean species, they possess an invisible and branchshaped internal parasitic organ (interna) and a visible and simplified external reproductive organ (externa) during the parasitic stage, lacking both segmentation and appendages (Høeg and Lützen 1995). Other organ systems such as the respiratory, digestive, sensory, and excretory systems are degenerate in adult rhizocephalans (Høeg 1992; Øksnebjerg 2000). As a result of this simplified external adult morphology, the previous taxonomy system of rhizocephalans relied on the examination of morphological characteristics of larva and histological characteristics of adult externa (Yoshida et al. 2011; Kobayashi et al. 2018), and this system was further verified and partially modified through DNA barcode and molecular phylogenetic analysis (Yoshida et al. 2012 2014; Høeg et al. 2019; Chan et al. 2021). Since the first report of parasitic barnacles Parasacculina pinnotherae in Korea (Shiino 1943), several systematic studies have been conducted on Korean parasitic barnacles (Lützen et al. 2016; Jung et al. 2019 2021). However, the rhizocephalan fauna in Korea has not yet been fully identified, as only a limited number of hosts have been investigated (Jung et al. 2019 2021). For example, Parasacculina oblonga (Lützen and Yamaguchi 1999) was first reported from the host crab Cyclograpsus intermedius in Japan, but parasitism of P. oblonga was not reported in Korean C. intermedius. Zoological Studies 63: 1 (2024) doi:10.6620/ZS.2024.63-01 1 © 2024 Academia Sinica, Taiwan Therefore, we also collected Korean rhizocephalans and identified them based on morphological examination and molecular analyses of mitochondrial cytochrome c oxidase subunit I (coxI). In addition, we made a checklist included detailed biological characteristics about each Korean rhizocephalan to help future research about Rhizocephala. MATERIALS AND METHODS We examined 64 Korean rhizocephalans from 15 host decapods collected from 21 sampling sites in Korea (Table 1). Voucher specimens in this study were deposited in the National Institute of Biological Resources (NIBR) and the Honam National Institute of Biological Resources (HNIBR). All rhizocephalan specimens were fixed in 70–95% ethanol and subjected to morphological examination and molecular analysis. For morphological analysis, the externa and mantle aperture were examined using an MZ8 dissection microscope (Leica, Wetzlar, Germany). Photographs were taken with a D200 digital camera (Nikon, Tokyo, Japan). The shield length (hermit crab) and carapace length (crab) of the host decapod were measured as the length from the tip of the rostrum to the midpoint of the posterior margin of the carapace using a CD6CSX digital caliper (Mitutoyo, Kawasaki, Japan) to the nearest 1 mm. For molecular analysis, the lateral end of the externa tissue of each rhizocephalan specimen was excised for total genomic DNA extraction using the QIAamp DNA Micro Kit (QIAGEN, Hilden, Germany). Universal primers LCO1490 (5'-GGTCAACAAAT CATAAAGATATTGG-3') and HCO2198 (5'-TAAA CTTCAGGGTGACCAAAAAATCA-3') were used to amplify a fragment of cox1 (Folmer et al. 1994). Polymerase chain reaction (PCR) was performed in reaction volumes of 50 µL that included 2 µL DNA template, 5 µL 10 x Ex Taq Buffer, 2 µL of each primer (10 µM), 0.25 µL Go Taq DNA polymerase (Promega, Madison City, WI, USA), 5 µL dNTP mix (10 mM), and 35.75 µL distilled H2O. PCR amplification was performed using the following steps: 5 min denaturation at 94°C followed by 35 cycles of 30 sec at 94°C, 1 min at 52°C, 1 min at 72°C, and a final extension of 7 min at 72°C. PCR products were visualized on 1% agarose gels and sequenced with an ABI PRISM 3730xl DNA analyzer (Applied Biosystems, Foster City, CA, USA). Nucleotide sequences of mtDNA cox1 fragments were analyzed and edited using Geneious v. 9.1.8 (Kearse et al. 2012). cox1 sequences in this study were deposited in GenBank (Table 1). Molecular identification of each sample was conducted through BLAST results of the sequences. To determine the fauna of Korean rhizocephalans, the results of morphological and molecular identification of the 64 individuals were combined with taxonomic information from previous studies of Korean Rhizocephala. RESULTS Based on the morphological examination of externae from 64 samples and information from 46 cox1 sequences, we identified 16 rhizocephalan species belonging to six genera, and four families i.e., Peltogasterellidae, Peltogastridae, Polyascidae, and Sacculinidae (Table 1). This study found that three species of rhizocephalans i.e., Parasacculina oblonga, Sacculina angulata, and Sacculina gracilis, had an expanded distribution range and were newly found in Korea. In addition, we found three new species candidates, i.e., Peltogasterella sp., Peltogaster sp., and Parasacculina sp. 1. As a result of including rhizocephalans reported in previous studies (Shiino 1943; Kim and Hong 2002; Lützen et al. 2016; Jung et al. 2019 2021), the presence of 22 rhizocephalans in Korea were identified. The distribution of Rhizocephala in South Korea is shown in figure 1, and a checklist was prepared for 16 species with confirmed species names and molecular data. Brief information on the externa morphology of 22 Korean rhizocephalans is presented in table 2. We provide brief remarks about noteworthy biological characteristics of Korean Rhizocephala, including comparisons to previous studies. Diagnoses and distribution information identical to previous studies (Jung et al. 2019 2021) are omitted. Checklist of Korean Rhizocephala Phylum Arthropoda von Siebold, 1848 Class Thecostraca Gruvel, 1905 Subclass Cirripedia Burmeister, 1834 Infraclass Rhizocephala Müller, 1862 Family Peltogasterellidae Høeg & Glenner in Høeg, Noever, Rees, Crandall & Glenner, 2019 Genus Peltogasterella Krüger, 1912 1. Peltogasterella gracilis (Boschma, 1927) Family Peltogastridae Lilljeborg, 1861 Genus Peltogaster Rathke, 1842 2. Peltogaster lineata Shiino, 1943 3. Peltogaster postica Yoshida & Osawa in Yoshida, Osawa, Hirose & Hirose, 2011 4. Peltogaster reticulata Shiino, 1943 Family Polyascidae Høeg & Glenner in Høeg, Noever, page 2 of 13Zoological Studies 63: 1 (2024) © 2024 Academia Sinica, Taiwan Ecoregion 50: Yellow Sea Ecoregion 52: East China Sea South Korea Ecoregion 49: East Sea (Sea of Japan) Goseong Sokcho Gangneung Samcheok Uljin Jeju Seogwipo Ulleung Incheon Taean Jindo Wando Shinan Busan Ulsan Pohang Yeongdeok Gyeongju Yeosu Namhae Tongyeong Goheung Boryeong Sacheon Buan Parasacculina imberbis Parasacculina pilosella Parasacculina yatsui Polyascus cf. gregarius Sacculina confragosa Peltogasterella gracilis Peltogaster postica Peltogaster sp. 1 Fig. 1. Distribution map of the eight most common Korean rhizocephalans. Blue dotted lines indicate divisions between ecoregions mentioned in Muhammad et al. (2022) and Kim et al. (2020 2022). Table 1. Geographical locations and sample information of Korean rhizocephalans in this study in order of species name, host species, location, and specimen number Species Host Species Location (Korea) Specimen Number coxI Accession Number Heterosaccus papillosus Charybdis (Charybdis) japonica Incheon NIBRIV0000895329 OR481955 NIBRIV0000895330 Parasacculina imberbis Pachygrapsus crassipes Jeju Koreakr10 OR481956 Seogwipo Koreax8 OR481963 Tongyeong Korearr54 OR481962 Parasacculina oblonga Cyclograpsus intermedius Ulleung DSEVIV0000000050 OR481965 DSEVIV0000000051 OR481966 DSEVIV0000000054 OR481967 DSEVIV0000000055 OR481968 DSEVIV0000000056 OR481969 page 3 of 13Zoological Studies 63: 1 (2024) © 2024 Academia Sinica, Taiwan Species Host Species Location (Korea) Specimen Number coxI Accession Number Parasacculina pinnotherae Arcotheres sinensis Jindo KoreaJD1 Parasacculina pilosella Pugettia intermedia Goseong GS 2381 Sokcho Korearr1 Parasacculina yatsui Cyclograpsus intermedius Ulleung Korearr40 Hemigrapsus penicillatus Gangneung Korearr10 Goseong GS12 Hemigrapsus sanguineus Goheung KoreaN14 OR481973 Goseong Korea71 OR481975 Tongyeong Korea39 OR481974 Pachygrapsus crassipes Gangneung Korearr9 OR481977 Jeju Koreakr9 OR481976 Samcheok Korearr25 OR481978 Yeongdeok Korea72 Parasacculina shiinoi Upogebia major Namhae Korea56 Parasacculina sp. 1 Hemigrapsus sanguineus Goheung Korea6N OR481970 Korea13N OR481971 Korea16N OR481972 Peltogasterella gracilis Pagurus maculosus Shinan Korea61 OR481992 Peltogasterella sp. Porcellanopagurus nihonkaiensis Jeju MADBK 160730_002 Seogwipo KoreaPN1 OR481994 Peltogaster reticulata Pagurus minutus Namhae MADBK 160706_065 MK604151* MADBK 160706_125 Pagurus proximus Shinan MADBK 160718_040 Peltogaster sp. 1 Pagurus lanuginosus Gangneung DSEVIV0000000053 OR481985 Pagurus maculosus Seogwipo DSEVIV0000000057 OR481986 Shinan DSEVIV0000000052 OR481987 KoreaHS1 OR481988 KoreaHS2 OR481989 KoreaHS3 OR481990 KoreaHS4 OR481991 Polyascus cf. gregarius Hemigrapsus sanguineus Busan Korearr60 OR482023 Goheung Korea1N OR481995 Jindo Koreakr1 OR482016 Shinan Korearr58 OR482022 Tongyeong Korearr56 OR482021 Wando Korea47 OR482011 Yeosu Korea45 OR482010 Sacculina angulata Thalamita sima Busan NIBRIV0000895328 OR482032 Sacheon NIBRIV0000895331 Sacculina confragosa Gaetice depressus Goheung Korea52 OR482037 Hemigrapsus sanguineus Gangneung Korearr22 OR482050 Goheung Korea7N OR482033 Jindo Koreakr2 OR482038 Pohang Korearr59 OR482062 Pachygrapsus crassipes Gangneung Korearr8 OR482049 Jeju Korea74 Samcheok Korearr53 OR482061 Seogwipo Koreakr11 OR482041 Sokcho Korea73 Uljin Korearr28 OR482053 Sacculina gracilis Thalamita sima Seogwipo NIBRIV0000895332 OR482063 Tongyeong NIBRIV0000895334 OR482064 Sacculina upogebiae Upogebia major Boryeong NIBRIV0000453552 Incheon NIBRIV0000453567 *: NCBI sequence. Table 1. (Continued) page 4 of 13Zoological Studies 63: 1 (2024) © 2024 Academia Sinica, Taiwan Rees, Crandall & Glenner, 2019 Genus Parasacculina Høeg & Glenner in Høeg, Noever, Rees, Crandall & Glenner, 2019 5. Parasacculina imberbis (Shiino, 1943) 6. Parasacculina pilosella (Van Kampen & Boschma, 1925) 7. Parasacculina pinnotherae (Shiino, 1943) 8. Parasacculina shiinoi (Lützen, Itani, Jespersen, Hong, Rees & Glenner, 2016) 9. Parasacculina yatsui (Boschma, 1936) 10. Parasacculina oblonga (Lützen & Yamaguchi, 1999) Genus Polyascus Glenner, Lützen & Takahashi, 2003 11. Polyascus cf. gregarius (Okada & Miyashita, 1935) Family Sacculinidae Lilljeborg, 1861 Genus Heterosaccus Smith, 1906 12. Heterosaccus papillosus (Boschma, 1933) Genus Sacculina Thompson, 1836 13. Sacculina upogebiae Shiino, 1943 14. Sacculina confragosa Boschma, 1933 15. Sacculina angulata Van Kampen & Boschma, 1925 16. Sacculina gracilis Boschma, 1931 Table 2. Morphological characteristics of externa of 22 Korean Rhizocephala Species Externa number Externa shape Mantle aperture Chitinous shield Host family Projection Opening Position Peltogasterella gracilis Gregarious Elongate banana-shaped Elevated Circular Terminal No Paguridae Peltogasterella sp. 1–3 Elongate Vestigial Circular Terminal No Paguridae Peltogaster lineata 1 Elongate oval Slightly elevated or elevated tube Circular Terminal or subterminal Yes Paguridae Peltogaster postica 1–2 Irregularly elongate Elevated tube U-shaped Terminal Yes Paguridae Peltogaster reticulata 1 Banana-shaped Elevated tube X-shaped Terminal Yes Paguridae Peltogaster sp. 1 1 Irregularly elongate Slightly elevated Circular Terminal or subterminal Yes Paguridae Peltogaster sp. 2 1 Irregularly elongate Terminal or subterminal Yes Diogenidae Parasacculina imberbis 1 Smooth round-rectangular or bilobed Slightly elevated X-shaped Terminal No Grapsidae Parasacculina pilosella 1Smooth and slightly flat oval Vestigial Circular Terminal No Epialtidae Parasacculina pinnotherae 1–2 Smooth or slightly wrinkled flat oval or cordiform Elevated Dot shaped Terminal No Pinnotheridae Parasacculina shiinoi 1 Smooth oval Vestigial Circular Terminal No Upogebiidae Parasacculina yatsui 1Slightly wrinkled flat oval or flat cordiform Elevated Slit shaped Terminal No Grapsidae, Varunidae Parasacculina oblonga 1 Smooth or slightly wrinkled oval Elevated Y-shaped Terminal No Varunidae Parasacculina sp. 1 1 Smooth or slightly wrinkled flat cordiform Slightly elevated Circular Terminal No Varunidae Parasacculina sp. 2 1 Smooth or slightly wrinkled oval Elevated Circular Terminal No Xanthidae Parasacculina sp. 3 1 Smooth oval Slightly elevated Circular Terminal No Xanthidae Polyascus cf. gregarius 1–3 Smooth or slightly wrinkled flat cordiform Elevated Slit shaped Terminal No Varunidae Heterosaccus papillosus 1 Smooth or slightly wrinkled reversed cordiform Slightly elevated or elevated Large circular Terminal No Portunidae Sacculina upogebiae 1 Oval with a very shallow groove along the dorsal margin Vestigial Circular Terminal No Upogebiidae Sacculina confragosa 1–2 Wrinkled flat cordiform Elevated tube Circular Terminal No Grapsidae, Varunidae Sacculina angulata 1–3 Slightly wrinkled irregular pentagon Elevated tube Large circular Terminal No Portunidae Sacculina gracilis 1 Smooth round fusiform Slightly elevated Y-shaped Terminal No Portunidae page 5 of 13Zoological Studies 63: 1 (2024) © 2024 Academia Sinica, Taiwan Peltogasterellidae Høeg & Glenner in Høeg, Noever, Rees, Crandall & Glenner, 2019 Peltogasterella Krüger, 1912 Peltogasterella gracilis (Boschma, 1927) (Fig. 2A, see Jung et al. 2019) Additional material examined: On Pagurus maculosus: 1 individual, Sinan, 34°40'55.1"N, 125°26'38.1"E, 26 Aug. 2021, collected by Jung J., Korea61, host: males, shield length 8 mm. Host species: Discorsopagurus schmitti, Labidochirus splendescens, Pagurus aleuticus, Pagurus dalli, Pagurus edwardsii, Pagurus filholi, Pagurus hemphilli, Pagurus hirsutiusculus, Pagurus lanuginosus, P. maculosus, Pagurus middendorffii, Pagurus nigrivittatus, Pagurus ochotensis, Pagurus pectinatus, Pagurus spina (Anomura). Peltogasterella sp. (Fig. 2B) Material examined: on Porcellanopagurus nihonkaiensis: 2 individuals (single individual with 2 externae), Jeju, 33°25'17.44"N, 126°9'38.96"E, Scuba, 24 Sep. 2011, collected by Lee SK., MADBK 160730_002, host: males, shield length 2 mm; 1 individual (3 externae), Seogwipo, 33°13'30.2"N, 126°34'11.9"E, Scuba 60 m, 11 Nov. 2020, collected by Lee SH., KoreaPN1, host: shield length 1 mm. Host species: P. nihonkaiensis (Anomura). Distribution: Korea. Diagnosis: Whole externa single to triple, smooth, and elongated oval in shape. Mantle aperture not well developed, and vertically small circular opening at the extremity. Peltogastridae Lilljeborg, 1861 Peltogaster Rathke, 1842 Peltogaster lineata Shiino, 1943 (see Jung et al. 2019) Host species: Pagurus brachiomastus, Pagurus filholi, Pagurus nigrivittatus, Pagurus maculosus (Anomura; Paguridae). Peltogaster postica Yoshida & Osawa in Yoshida, Osawa, Hirose & Hirose, 2011 (see Jung et al. 2019) Host species: Pagurus filholi, P. minutus, P. nigrivittatus, Pagurus angustus (Anomura; Paguridae). Peltogaster reticulata Shiino, 1943 (see P. aff. reticulata and Peltogaster sp. 4 of Jung et al. 2019) Material reexamined: on P. minutus: 1 individual, Namhae, 34°52'40.83"N, 127°56'43.61"E, 14 Nov. 2012, collected by Jung J, MADBK 160706_065, host: female, shield length 4 mm; 1 individual (2 externae)., Namhae, 34°52'40.83"N, 127°56'43.61"E, 12 May 2018, collected by Jung J, MADBK 160706_125, host: female, shield length 3 mm. On P. proximus: 1 individual, Shinan, 34°35'49.24"N, 125°45'58.02"E, 16 Oct. 2008, collected by Hong J, MADBK 160718_040, host: female, shield length 3 mm. Host species: Pagurus constans, P. minutus, Pagurus proximus (Anomura; Paguridae). Distribution: Japan (type locality), Russia, Korea. Peltogaster sp. 1 (Fig. 2C) Material examined: on P. lanuginosus: 1 individual, Gangneung, 37°44'04.3"N, 128°59'25.8"E, 23 Oct. 2021, collected by Jung J., DSEVIV0000000053. On P. maculosus: 1 individual, Sinan, 34°40'55.1"N, 125°26'38.1"E, 26 Aug. 2021, collected by Jung J., DSEVIV0000000052, KoreaHS1-KoreaHS4, host: females, shield length 8 mm; Seogwipo, 33°14'05.1"N, 126°21'30.1"E, 6 Sep. 2021, DSEVIV0000000057, host: shield length 9 mm. Host species: P. lanuginosus, P. maculosus (Anomura; Paguridae). Distribution: Korea. Diagnosis: Whole externa single, smooth, and irregular oval in shape. Mantle aperture slightly elevated or elevated tube, and vertically circular opening at the extremity. Peltogaster sp. 2 (see Peltogaster sp. 3 at Jung et al. 2019) Host species: Paguristes ortmanni (Anomura; Diogenidae). Polyascidae Høeg & Glenner in Høeg, Noever, Rees, Crandall & Glenner, 2019 Parasacculina Høeg & Glenner in Høeg, Noever, Rees, Crandall & Glenner, 2019 Parasacculina imberbis (Shiino, 1943) (Fig. 2D, see Jung et al. 2021) Additional materials examined: on Pachygrapsus crassipes: 1 individual, Seogwipo, 33°14'09.6"N, page 6 of 13Zoological Studies 63: 1 (2024) © 2024 Academia Sinica, Taiwan 126°21'35.4"E, 6 Sep. 2021, collected by Jung J., Koreax8, host: ♀, carapace length 14 mm; 1 individual, Tongyeong, 34°45'31.3"N, 128°30'59.4"E, 29 Oct. 2021, collected by Jung J., Korearr54; 1 individual, Jeju, 33°30'57.3"N, 126°30'38.5"E, 23 Aug. 2022, collected by Jung J., Koreakr10. Host species: P. crassipes (Brachyura; Grapsidae). Diagnosis: Whole externa single, smooth or slightly wrinkled, and slightly bilobed with half-ovalshaped left and right lobes divided by a mid-notch. Mantle aperture slightly elevated as short tube shape and vertically circular opening at the extremity. Color: yellow. Parasacculina pilosella (Van Kampen & Boschma, 1925) (Fig. 2E, see Jung et al. 2021) Additional materials examined: on Pugettia intermedia: 1 individual, Sokcho, 38°13'38.1"N, 128°35'16.1"E, 8 Sep. 2020, Korearr1; 1 individual, Goseong, 38°27'01.3"N, 128°28'03.9"E, 25 Sep. 2021, GS 2381. Host species: P. intermedia, Pugettia aff. ferox (Brachyura; Epialtidae). Parasacculina pinnotherae (Shiino, 1943) (see Jung et al. 2021) Additional materials examined: on Arcotheres sinensis: 3 individuals, Jindo, 34°23'16.9"N, 126°17'20.8"E, 23 July 1994, KoreaJD1. Host species: A. sinensis (Brachyura; Pinnotheridae). Parasacculina shiinoi (Lützen, Itani, Jespersen, Hong, Rees & Glenner, 2016) (see Jung et al. 2021) Additional materials examined: on Upogebia major: 1 individual, Namhae, 34°52'40.83"N 127°56'43.61"E, 26 Sep. 2021, collected by Jung J., Korea56. Host species: U. major (Gebiidea; Upogebiidae). Diagnosis: Whole externa single, smooth, and irregular oval shape with a shallow median groove on dorsal margin. Mantle aperture vestigial and vertically large circular opening with radiated ridges at the extremity. Parasacculina yatsui (Boschma, 1936) (Fig. 2F, see Jung et al. 2021) Additional materials examined: on Cyclograpsus intermedius: 1 individual, Ulleung, 37°28'32.4"N, 130°53'51.5"E, 19 Sep. 2019, collected by Jung J., Korearr40. On Hemigrapsus penicillatus: 1 individual, Goseong, 38°16'11.5"N, 128°33'27.2"E, 26 Sep. 2021, collected by Jung J., GS12, host: ♂, carapace length 20 mm; 1 individual, Gangneung, 37°44'04.3"N, 128°59'25.8"E, 23 Oct. 2021, collected by Jung J., Korearr10. On Hemigrapsus sanguineus: 1 individual, Goheung, 34°30'22.2"N, 127°28'56.0"E, 9 Oct. 2022, collected by Jung J., KoreaN14; 1 individual, Goseong, 38°27'01.3"N, 128°28'03.9"E, 25 Sep. 2021, collected by Jung J., Korea71, host: ♀, carapace length 19 mm; 1 ind, Tongyeong, 34°38'24.9"N, 128°34'06.1"E, 19 Aug. 2019, collected by Jung J., Korea39, host: ♂, carapace length 14 mm. On P. crassipes: 1 individual, Yeongdeok, 36°16'22.0"N, 129°22'44.3"E, 29 Aug. 2021, collected by Jung J., Korea72, host: ♀, carapace length 22 mm; 1 individual, Gangneung, 37°44'04.3"N, 128°59'25.8"E, 23 Oct. 2021, collected by Jung J., Korearr9; 1 individual, Samcheok, 37°12'50.5"N, 129°20'46.5"E, 19 May 2022, collected by Jung J., Korearr25; 1 individual, Jeju, 33°30'57.3"N, 126°30'38.5"E, 23 Aug. 2022, collected by Jung J., Koreakr9. Host species: P. crassipes (Brachyura; Grapsidae), H. sanguineus, H. penicillatus, C. intermedius (Brachyura; Varunidae). Parasacculina oblonga (Lützen & Yamaguchi, 1999) (Korean name: Bi-Dan-Ge-Yeop-Ju-Meo-Ni-Beol-Rae) (Fig. 2G) Material examined: on C. intermedius: 1 individual, Ulleung, 37°28'32.4"N, 130°53'51.5"E, 3 June 2021, collected by Jung J., DSEVIV0000000050 host: ♀, carapace length 12 mm; 1 individual, Ulleung, 37°28'32.4"N, 130°53'51.5"E, 3 June 2021, collected by Jung J., DSEVIV0000000051, host: ♀, carapace length 12 mm; 1 individual, Ulleung, 37°28'32.4"N, 130°53'51.5"E, 19 Sep. 2019, collected by Jung J., DSEVIV0000000054; 1 individual, Ulleung, 37°30'49.9"N, 130°47'45.0"E, 18 Sep. 2019, collected by Jung J., DSEVIV0000000055; 1 individual, Ulleung, 37°30'49.9"N, 130°47'45.0"E, 18 Sep. 2019, collected by Jung J., DSEVIV0000000056, host: ♂, carapace length 14 mm. Host species: C. intermedius (Brachyura; Varunidae). Distribution: Japan (type locality), Korea. Diagnosis: Whole externa single, smooth or slightly wrinkled, and oval in shape. Mantle aperture large, elevated, and vertically Y-shape opening at the page 7 of 13Zoological Studies 63: 1 (2024) © 2024 Academia Sinica, Taiwan extremity. Parasacculina sp. 1 (Fig. 2H) Material examined: on H. sanguineus: 1 individual, Goheung, 34°31'7.0"N, 127°26'12.2"E, 8 Oct. 2022, collected by Jung J and Park J-K., HVBNIV0000000005, host: ♀, carapace length 24 mm; 1 individual, Goheung, 34°30'22.2"N, 127°28'56.0"E, 9 Oct. 2022, collected by Jung J., Korea13N, host: ♀, carapace length 33 mm; 1 individual, Goheung, 34°30'22.2"N, 127°28'56.0"E, 9 Oct. 2022, collected by Jung J. and Park J-K, HVBNIV0000000006, host: ♀, carapace length 25 mm. Host species: H. sanguineus (Brachyura; Varunidae). Distribution: Korea. Diagnosis: whole externa smooth, single, and cordiform with flat half-oval-shaped left and right Fig. 2. Externae of Korean rhizocephalans in this study. Blue arrow: mantle aperture, scale bar: 2 mm for H and J, 1mm for A-G, I, K, L. A, Peltogasterella gracilis; B, Peltogasterella sp.; C, Peltogaster sp. 1; D, Parasacculina imberbis; E, Parasacculina pilosella; F, Parasacculina yatsui; G, Parasacculina oblonga; H, Parasacculina sp. 1; I, Polyascus cf. gregarius; J, Heterosaccus papillosus; K, Sacculina angulata; L, Sacculina gracilis. Externae of C and H are incomplete, because they were sampled for molecular analysis. page 8 of 13Zoological Studies 63: 1 (2024) © 2024 Academia Sinica, Taiwan lobes divided by outer mid-groove and inner mid-ridge. Mantle aperture slightly elevated, and slightly wrinkled with circular opening at extremity. Parasacculina sp. 2 (see Parasacculina sp. 1 of Jung et al. 2021) Host species: Macromedaeus distinguendus (Brachyura; Xanthidae). Parasacculina sp. 3 (see Parasacculina sp. 2 of Jung et al. 2021) Host species: Macromedaeus distinguendus (Brachyura; Xanthidae). Polyascus Glenner, Lützen & Takahashi, 2003 Polyascus cf. gregarius (Okada & Miyashita, 1935) (Fig. 2I, see Polyascus cf. gregarius of Jung et al. 2021) Additional materials examined: on H. sanguineus: 1 individual, Yeosu, 34°29'22.4"N, 127°48'49.5"E, 11 May 2021, collected by Jung J., Korea45, 1 individual, Wando, 34°17'47.4"N, 126°42'05.1"E, 24 May 2021, collected by Jung J., Korea47, host: ♂, carapace length 34 mm; 1 individual, Tongyeong, 34°45'31.3"N, 128°30'59.4"E, 29 Oct. 2021, collected by Jung J., Korearr56; 1 individual, Shinan, 24 May 2016, collected by Jung J., Korearr58; 1 individual, Busan, 13 May 2020, collected by Jung J., Korearr60; 1 ind, Jindo, 34°31'24.4"N, 126°12'56.5"E, 6 July 2022, collected by Jung J., Koreakr1; 1 individual, Goheung, 34°31'7.0"N, 127°26'12.2"E, 8 Oct. 2022, collected by Jung J., Korea1N. Host species: H. sanguineus, H. takanoi, Eriocheir japonica (Brachyura; Varunidae). Sacculinidae Lilljeborg, 1861 Heterosaccus Smith, 1906 Heterosaccus papillosus (Boschma, 1933) (Fig. 2J) Material examined: on Charybdis (Charybdis) japonica: 1 individual, Incheon, 37°15'54.2"N, 126°29'51.8"E, 23 Aug. 2012, NIBRIV0000895329; 1 individual, Incheon, 37°24'31.4"N, 126°38'41.0"E, 18 Aug. 1998, NIBRIV0000895330. Host species: Charybdis (Gonioneptunus) bimaculata, C. (C.) japonica Brachyura; (Portunidae). Distribution: Philippines (type locality), Japan, Korea. Diagnosis: Whole externa single, smooth or slightly wrinkled, and reversed cordiform with left and right lobes divided by a mid-notch. Mantle aperture slightly elevated or elevated, radically wrinkled, and vertically large circular opening at the extremity. Sacculina Thompson, 1836 Sacculina confragosa Boschma, 1933 (see Jung et al. 2021) Additional materials examined: on Gaetice depressus: 1 individual, Goheung, 34°24'56.9"N, 127°29'36.5"E, 12 May 2021, collected by Jung J., Korea52, host: ♂, carapace length 18 mm. on P. crassipes: 1 individual, Sokcho, 38°12'50.9"N, 128°36'05.5"E, 6 Sep 2021, collected by Jung J., Korea73, host: ♀, carapace length 17 mm; 1 individual, Jeju, 33°56'40.8"N, 126°20'03.5"E, 7 Sep 2021, collected by Jung J., Korea74, host: ♀, carapace length 14 mm; 1 individual, Gangneung, 37°44'04.3"N, 128°59'25.8"E, 23 Oct. 2021, collected by Jung J., Korearr8; 1 individual, Uljin, 37°03'32.7"N, 129°25'46.0"E, 24 Oct. 2022, collected by Jung J., Korearr28; 1 individual, Samcheok, 37°08'51.2"N, 129°21'48.9"E, 19 May 2022, collected by Jung J., Korearr53; 1 ind, Seogwipo, 33°12'28.3"N, 126°17'30.7"E, 21 Aug. 2022, collected by Jung J., Koreakr11. on H. sanguineus: 1 individual, Gangneung, 37°44'04.3"N, 128°59'25.8"E, 18 May 2022, collected by Jung J., Korearr22; 1 individual, Pohang, 36°00'14.4"N, 129°34'32.1"E, 11 May 2020, collected by Jung J., Korearr59; 1 ind, Jindo, 34°31'25.0"N, 126°12'06.4"E, 6 July 2022, collected by Jung J., Koreakr2; 1 ind, Goheung, 34°31'7.0"N, 127°26'12.2"E, 8 Oct. 2022, collected by Jung J., Korea7N. Host species: G. depressus, P. crassipes (Brachyura; Grapsidae), C. intermedius, H. sanguineus (Brachyura; Varunidae). Sacculina angulate Van Kampen & Boschma, 1925 (Korean name: O-Gak-Ge-Ju-Meo-Ni-Beol-Rae) (Fig. 2K) Material examined: on Thalamita sima: 1 individual (3 externae, 1 externa removed for molecular analysis), Busan, 35°9'6.4"N, 129°10'43.1"E, 25 Apr. 2018, collected by SH Kim, NIBRIV0000895328 host: ♂, carapace length 23 mm; 1 individual, Sacheon 34°53'2.0"N, 128°4'34.6"E, 16 July 2014, collected by SH Kim, NIBRIV0000895331, host: ♀, carapace length 25 mm. Host: Xiphonectes longispinosus, C. (G.) bimaculata, T. sima (Brachyura; Portunidae). Distribution: Indonesia (type locality), Thailand, page 9 of 13Zoological Studies 63: 1 (2024)