A new Hemicyclops (Copepoda, Cyclopoida, Clausidiidae) associated with the scleractinian coral Galaxea from the South China Sea

93 A new Hemicyclops (Copepoda, Cyclopoida, Clausidiidae) associated with the scleractinian coral Galaxea from the South China Sea Il-Hoi Kim1, Jia Wang2, Viatcheslav N. Ivanenko2,3 1 Korea Institute of Coastal Ecology, 302-802, Seokcheon-ro 397, Bucheon 14449, Republic of Korea 2 Biological Faculty, Shenzhen MSU-BIT University, Shenzhen 518172, China 3 Department of Invertebrate Zoology, Lomonosov Moscow State University, Moscow 119992, Russia Corresponding authors: Jia Wang ([email protected]); Viatcheslav N. Ivanenko (iv[email protected]) Copyright: © Il-Hoi Kim et al. This is an open access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International – CC BY 4.0). Research Article Abstract The genus Hemicyclops Boeck, 1873 is known for its association with various marine invertebrates, including cnidarians, crustaceans, polychaetes, and sponges, with some species also occurring in planktonic communities. Here, we report the first association of Hemicyclops with the scleractinian coral Galaxea fascicularis (Linnaeus, 1767) (Scleractinia, Euphylliidae). Hemicyclops cyanus sp. nov. is described based on a female specimen collected from this coral host in the lagoon (depth 10 m) of Dongsha Atoll, Pratas Islands, South China Sea. The new species is readily distinguished from its congeners by its characteristic genital double-somite, which bears prominent anterolateral expansions, and by the flexed, elongated exopodal segment of leg 5, which is more than three times longer than wide. In H. cyanus sp. nov., the paired spermatophores attached to the female are fused into a butterfly-shaped, highly modified complex with large lateral wings and a central tube into which the female urosome is inserted. To aid in species identification, we present the first comparative plate with schematic illustrations of the genital double-somites for the group of 25 species, including the type species. Key words: Association, Copepoda, coral host, Crustacea, new species, Scleractinia, symbiosis, taxonomy Introduction Copepods are among the most diverse and ecologically significant crustaceans in the ocean, with numerous species forming symbiotic associations with scleractinian corals (Humes 1985a; Korzhavina and Ivanenko 2021). Based on at least 1195 documented records, these associations involve at least 384 species of copepods belonging to 117 genera and 29 families, and 172 species of corals belonging to 67 genera and 16 families (Korzhavina and Ivanenko 2021). Despite the high diversity and abundance of these copepods, only a fraction of potential coral hosts has been studied, and most research has been limited to a few geographic regions, leaving major gaps in knowledge of their taxonomy, host specificity, and biogeography. Academic editor: Kai Horst George Received: 13 August 2025 Accepted: 14 October 2025 Published: 18 November 2025 ZooBank: https://zoobank. org/850D7FC4-63D2-4B85-A802E2AD3E5FBAA2 Citation: Kim I-H, Wang J, Ivanenko VN (2025) A new Hemicyclops (Copepoda, Cyclopoida, Clausidiidae) associated with the scleractinian coral Galaxea from the South China Sea. ZooKeys 1260: 93–109. https://doi. org/10.3897/zookeys.1260.168539 ZooKeys 1260: 93–109 (2025) DOI: 10.3897/zookeys.1260.168539 94 ZooKeys 1260: 93–109 (2025), DOI: 10.3897/zookeys.1260.168539 Il-Hoi Kim et al.: New Hemicyclops from a coral of the South China Sea The Indo-Pacific coral genus Galaxea Oken, 1815 (Scleractinia Bourne, 1900; Euphylliidae Milne Edwards & Haime, 1857) is an important reef-builder and a host for at least 18 copepod species in eight genera, belonging to the orders Cyclopoida Burmeister, 1834 and Siphonostomatoida Burmeister, 1835 (Humes 1979, 1985a, b, 1991, 1996; Cheng et al. 2016; Cheng and Dai 2018). Cyclopoida includes 11 species of Anchimolgidae Humes & Boxshall, 1996, two species of Xarifiidae Humes, 1960, and one species of Pterinopsyllidae Sars, 1913. Siphonostomatoida includes four species of Asterocheridae Giesbrecht, 1899. Most copepod records come from Galaxea fascicularis (Linnaeus, 1767), followed by G. astreata (Lamarck, 1816), with occasional finds on G. horrescens (Dana, 1846) or unidentified Galaxea species. These copepod communities occur in many parts of the Indo-Pacific, including the Moluccas, New Caledonia, Australia, Madagascar, and Dongsha Atoll in the northern South China Sea. Dongsha Atoll is a biodiversity hotspot for Galaxea-associated copepods, with eight recorded species, two of which were first described from this atoll by Cheng and Dai (2018). The atoll also serves as a stepping-stone for larval dispersal and genetic connectivity among coral reefs in the South China Sea (Liu et al. 2021) and may function as a thermal refuge for reef-building corals under climate change (Tkachenko and Soong 2017). However, repeated disturbances such as typhoons, mass bleaching, and human activities have reduced coral cover, raising concerns about long-term reef decline (Cheng et al. 2020). Here, we describe a new species of Hemicyclops Boeck, 1873 (Copepoda, Cyclopoida, Clausidiidae Embleton, 1901) found on the scleractinian coral Galaxea, as part of a broader study on the biodiversity of coralassociated copepods. Material and methods Symbiotic copepods were collected from colonies of Galaxea fascicularis at the Dongsha Atoll, Pratas Islands, South China Sea (see Suppl. material 1: figs S1–S5), using a boat and SCUBA diving, applying the method described by Ivanenko et al. (2018). Coral specimens were obtained from depths of 10 m and placed into resealable plastic bags underwater. Upon retrieval to the surface, each bag with corals was filled with a 10% ethanol solution to preserve the associated fauna. After approximately 30 minutes, the bags were gently agitated, and the preservation fluid was filtered through a 100 μm mesh sieve. The retained material was transferred to a Petri dish for the selection of copepods under a stereomicroscope. Selected specimens were preserved in 95% ethanol and stored at −20 °C. Prior to microscopic examination, specimens were cleared in lactic acid for approximately 10 minutes. Dissections followed the reverse slide method described by Humes and Gooding (1964). Appendage lengths were measured, with reported values representing the mean of the maximum and minimum measurements. The holotype is deposited in the Honam National Institute of Biological Resources (HNIBR). 95 ZooKeys 1260: 93–109 (2025), DOI: 10.3897/zookeys.1260.168539 Il-Hoi Kim et al.: New Hemicyclops from a coral of the South China Sea Taxonomy Order Cyclopoida Burmeister, 1834 Family Clausidiidae Embleton, 1901 Genus Hemicyclops Boeck, 1873 Hemicyclops cyanus sp. nov. https://zoobank.org/0C5566E0-E628-4749-A9C2-4DA06FB2943F Figs 1–3 Type material. Holotype: One dissected ♀ mounted on 3 slides (HNIBRIV18791). Type locality. 20°38'03.1"N, 116°49'30.5"E, Lagoon of Dongsha Atoll, Pratas Islands, the South China Sea, depth 10 m, 12 October 2017. Collector: V.N. Ivanenko. Host. Galaxea fascicularis (Linnaeus, 1767) (Scleractinia, Euphylliidae). Etymology. The name is derived from the Greek “cyan” (meaning “bluegreen”), referring to the blue-green colour of the holotype. Description. Female. Body (Fig. 1A) rather narrow, with a vivid blue-green colour all over. Prosome 732 × 477 μm, consisting of the cephalothorax and second to fourth pedigerous somites, with nearly parallel lateral margins. Cephalothorax 436 μm long, wider than long, with projected and acutely pointed posterolateral corners. The second and third pedigerous somites bearing a membranous fringe along their posterodorsal margin. Urosome (Figs 1B, 2A) 5-segmented. First urosomal somite (fifth pedigerous somite) 163 μm wide, with a membranous fringe along the posterodorsal margin. The genital double-somite 1.08 times longer than wide (330 × 309 μm); its anterior 40% wing-like, expanded laterally, tapering towards posterolaterally, with a blunt apex. Genital aperture (Fig. 1D; indicated by arrowhead) positioned dorsolaterally at the proximal region of the expanded part. Each posterolateral region of this expanded part bearing a small copulatory pore (Fig. 2B; indicated by arrowhead). The narrower posterior 60% part of the double-somite bearing 1 small tubercle on each lateral margin and 1 plate-like ventral organ (Fig. 2B) on the anteroventral region, with 7 pores along the distal margin. The genital double-somite and three abdominal somites with a membranous fringe along their posteroventral margin. The three abdominal somites are short, measuring 45 × 106, 30 × 103, and 36 × 102 μm, respectively. The anal somite bears a large anal aperture. Spermatophore complex (Fig. 1B, C), formed by the fusion of the original pair of spermatophores, is strongly modified, with a tube-like medial region encircling the urosome and wing-like lateral expansions, each bearing lateral and posterior apices. Each spermatophore internally contains bubble-like transparent globules of irregular sizes; a space is present lateral to the spermatophore. Caudal rami (Fig. 1E) widely separated from each other; each ramus 1.15 times longer than wide (45 × 39 μm), bearing two transverse rows of fine setules on the inner side, one minute proximal setule (rudimentary seta I) on the outer margin, and six setae (setae II–VII). Seta IV (outer distal seta) proximally modified as a spine tipped with a unilaterally pinnate seta. Rostrum small, triangular, with a blunt posterior apex. 96 ZooKeys 1260: 93–109 (2025), DOI: 10.3897/zookeys.1260.168539 Il-Hoi Kim et al.: New Hemicyclops from a coral of the South China Sea Figure 1. Hemicyclops cyanus sp. nov., female. A. Habitus with spermatophore; B. Urosome with spermatophore, ventral; C. Spermatophore; D. Left side of anterior part of urosome, dorsal; E. Anal somite and caudal rami, dorsal. Scale bars: 0.1 mm (A–C); 0.05 mm (D, E). 97 ZooKeys 1260: 93–109 (2025), DOI: 10.3897/zookeys.1260.168539 Il-Hoi Kim et al.: New Hemicyclops from a coral of the South China Sea Figure 2. Hemicyclops cyanus sp. nov., female. A. Urosome, dorsal; B. Genital double-somite, ventral; C. Ventral organ of genital double-somite; D. Antennule; E. Antenna; F. Labrum; G. Labium; H. Mandible; I. Maxillule; J. Maxilla. Scale bars: 0.1 mm (A, B); 0.02 mm (C, H–J); 0.05 mm (D–G). 98 ZooKeys 1260: 93–109 (2025), DOI: 10.3897/zookeys.1260.168539 Il-Hoi Kim et al.: New Hemicyclops from a coral of the South China Sea Antennule (Fig. 2D) 354 μm long, 7-segmented; armature formula: 4, 14, 6, 3, 4+aesthetasc, 2+aesthetasc, and 7+aesthetasc; fifth to terminal segments each with 2, 1, and 4 pinnate setae, respectively; all other setae naked; aesthetascs thin, setiform. Antenna (Fig. 2E) 4-segmented, consisting of the coxobasis and 3-segmented endopod; coxobasis with 1 large seta at the mediodistal region, 3 patches of several setules on the margins; first endopodal segment slightly shorter than coxobasis, bearing 1 spinulose seta on the inner margin and setules or spinules on both margins; second endopodal segment expanded mediodistally (but lacking a digitiform projection), armed with 4 setae (the second proximal seta ornamented with spinules along the inner margin) and several spinules on the inner margin; third endopodal segment wider than long, 24 × 27 μm, subquadrate, bearing 7 setae, one of them spinulose, the others (including 4 geniculated ones) naked. Labrum (Fig. 2F) broad, with a row of spinules along the posterior margin. Labium (Fig. 2G) bearing a row of fine spinules along the anterior margin, 1 tooth at each side of the anterior margin, and 5 spinules on the ventral surface near the anterior margin. Mandible (Fig. 2H) armed distally with 1 stout spine bearing 2 rows of 3 denticles, 1 flabelliform spine, and 2 pinnate setae. Maxillule (Fig. 2I) distally bilobed; smaller inner lobe with 3 setae, one of them spiniform; larger outer lobe with 5 pinnate setae. Maxilla (Fig. 2J) 2-segmented; syncoxa (proximal segment) with 2 spinulose, spiniform setae of equal length, one of them bearing 1 small subsidiary seta at the proximal region; basis (distal segment) with 1 naked ventral seta, distal projection tipped with 3 unequal spines (one of them bearing 2 spinules), 1 spinulose seta, and 1 large, flabelliform spine. Maxilliped (Fig. 3A) consisting of the syncoxa, basis, and 2-segmented endopod; syncoxa (first segment) with 2 large, equal setae, one of them feebly pinnate, the other bearing several spinules; basis (second segment) longest, armed with 2 large spinulose setae at the apex of the projected proximal third and ornamented with about 17 setae at the mediodistal region, one of these spinules separated from the others (Fig. 3B); first endopodal segment (third segment) small, unarmed; second endopodal segment (Fig. 3C) forming a long claw, proximally bearing 1 strong spine bearing 4 denticles, 2 naked setae, and 1 small spine bearing 1 setule subdistally. Legs 1 (Fig. 3D), 2 (Fig. 3E), 3, and 4 (Fig. 3G) biramous, with 3-segmented rami. The intercoxal plate bearing setules in leg 1 and spinules in legs 2–4. The inner coxal seta is large, stiff, and spiniform in legs 2–4. Leg 3 is similar to leg 2, except bearing 4 spines and 2 setae on the third endopodal segment (Fig. 3F). The outer seta on the basis is large in legs 1 and 4, but small in legs 2 and 3. The mid-distal margin of the basis is ornamented with setules in leg 1 but with spinules in legs 2–4. The inner distal spine on the basis of leg 1 is large, extending to the distal margin of the second endopodal segment. The inner distal margin of the basis of leg 1 has a row of spinules near the base of the inner distal spine. The inner surface of the basis of legs 2–4 bears several spinules. The inner distal process of the third endopodal segment of legs 2–4 is unequally bifurcated. The distal seta on the third endopodal segment of leg 1 is small and naked. The distal flagellum is found on 5 distal spines in leg 1 and 2 distal spines in legs 2–4. 99 ZooKeys 1260: 93–109 (2025), DOI: 10.3897/zookeys.1260.168539 Il-Hoi Kim et al.: New Hemicyclops from a coral of the South China Sea Figure 3. Hemicyclops cyanus sp. nov., female. A. Maxilliped; B. Distal part of maxilliped basis; C. Terminal segment of maxilliped; D. Leg 1; E. Leg 2; F. Endopod of leg 3; G. Leg 4; H. Leg 5. Scale bars: 0.05 mm (A, D–H); 0.02 mm (B, C). 100 ZooKeys 1260: 93–109 (2025), DOI: 10.3897/zookeys.1260.168539 Il-Hoi Kim et al.: New Hemicyclops from a coral of the South China Sea Armature formula for legs 1-4 as follows: Leg 5 (Figs 1D, 3H) 2-segmented; protopod (proximal segment) wider than long, articulated from somite, armed with 1 long, slender, pinnate distodorsal seta and ornamented with setules and spinules near the base of the seta; exopodal segment 3.37 times longer than wide (118 × 35 μm), curved near the middle, armed with 3 spines and 1 pinnate seta, and ornamented with spinules along the outer and inner margins. The spine on the outer margin is naked, 51 μm long; the outer distal spine is 58 μm long; the distal seta is 55 μm long; the large inner distal spine is 82 μm long, slightly curved, bearing long, brush-like setules along approximately the proximal half of the inner margin. Leg 6 not visible in dorsal view of genital aperture (Fig. 2D). Male. Unknown. Discussion The new species was found on Galaxea fascicularis and is the first record of Hemicyclops from the coral family Euphylliidae. Hemicyclops is a diverse genus with 50 known species (Walter and Boxshall 2025). These copepods are reported from many hosts, often living in their burrows, and have been found on sponges, cnidarians, crustaceans, polychaetes, and mollusks, as well as in plankton. Records from scleractinian corals are rare, with only two known cases: H. columnaris Humes, 1984 from Porites lobata Dana, 1846 (Poritidae Gray, 1840) in Panama, and H. apiculus Humes, 1995 from Favia De Blainville, 1820 (Faviidae Milne Edwards & Haime, 1857) and Dendrophyllia de Blainville, 1830 (Dendrophylliidae Gray, 1847) in Madagascar (Humes 1984, 1995). The present finding adds Euphylliidae to the host range of the genus. As only one specimen was collected, it is unclear whether this species is an obligate associate of Galaxea or another invertebrate living in the coral tissues or skeleton. After analyzing the diagnostic features of existing Hemicyclops species, we found that eight species were insufficiently described, and the remaining 42 can be divided into Groups I and II. Group I includes atypical species (N = 17) with distinctive morphological traits that differ from the typical morphology of the genus. Group II consists of typical species (sensu stricto group) (N = 25) that share with H. cyanus sp. nov. the following core diagnostic features of the genus and serve as a reference for species identification: (1) the urosome is 5-segmented in the female and 6-segmented in the male; (2) the antennule is 7-segmented and bears four setae on the first segment, with no specified seta on the second; (3) the second endopodal segment (third segment) of the antenna bears four setae and lacks a claw; (4) the syncoxa (first segment) of the male maxilliped bears a single seta; (5) the basis of male leg 1 lacks an inner distal spine; and (6) the swimming legs have the usual number of armature elements (armature elements on the exopod and endopod of legs 1–4 are 8 and 6 in leg 1; 9 and 6 in legs 2 and 3; and 8 and 5 in leg 4, respectively). Coxa Basis Exopod Endopod Leg 1 0-1 1-I I-0; I-1; III, I, 4 0-1; 0-1; I, 5 Leg 2 0-1 1-0 I-0; I-1; III, I, 5 0-1; 0-2; I, II, 3 Leg 3 0-1 1-0 I-0; I-1; III, I, 5 0-1; 0-2; I, II, I+2 Leg 4 0-1 1-0 I-0; I-1; II, I, 5 0-1; 0-2; I, II, II 101 ZooKeys 1260: 93–109 (2025), DOI: 10.3897/zookeys.1260.168539 Il-Hoi Kim et al.: New Hemicyclops from a coral of the South China Sea Group I The following 17 species possess unusual morphological features in the female that clearly distinguish them from H. cyanus sp. nov. and other congeners: 1. H. acanthophorus Humes, 1995 — second endopodal segment of the antenna with 1 claw and 3 setae; labrum modified with digitiform lateral lobes; third exopodal segment of leg 3 with 8 (not 9) elements (Humes 1995). 2. H. acanthosquillae Humes, 1965 — second endopodal segment of the antenna with an elongated mediodistal projection more than twice as long as wide (Humes 1965). 3. H. cornutus Kim & Hong, 2014 — fifth pedigerous somite with a posterolateral hook (Kim and Hong 2014). 4. H. ctenidis Ho & Kim, 1990 — antennule 6-segmented; second endopodal segment of leg 4 with a single inner seta (Ho and Kim 1990). 5. H. cylindraceus (Pelseneer, 1929) — first antennular segment with 5 setae; second endopodal segment of the antenna with 2 claws and 2 setae; female urosome 6-segmented; terminal claw of the female maxilliped elongated, as in the male (Stock 1954). 6. H. diremptus Humes, 1965 — genital double-somite divided by a transverse suture line (Humes 1965). 7. H. livingstoni (Scott T, 1894) — first antennular segment with 5 setae; second endopodal segment of the antenna with 2 claws and 2 setae; female maxilliped with a large terminal claw, as in the male (Scott 1894). 8. H. membranatus Moon & Kim, 2010 — first antennular segment with 5 setae; second endopodal segment of the antenna with 1 claw and 3 setae (Moon and Kim 2010). 9. H. nasutus Moon & Kim, 2010 — first antennular segment with 5 setae (Moon and Kim 2010). 10. H. nichollsi Karanovic, 2008 — first antennular segment with 5 setae (Karanovic 2008). 11. H. perinsignis Humes, 1973 — first antennular segment with 5 setae; second endopodal segment of the antenna with 1 claw and 3 setae; third exopodal segment of leg 4 with 9 (not 8) elements (Humes 1973). 12. H. rapax Lee, Chang & Kim, 2022 — female maxilliped of the male type, with a large terminal claw (Lee et al. 2022). 13. H. sebastiani Kihara & Rocha, 1993 — first antennular segment with 5 setae; second segment of the antennule with 1 enlarged seta at the posterodistal corner; third endopodal segment of leg 1 with 1 spine and 4 setae (Kihara and Rocha 1993). 14. H. spinulosus Itoh & Nishida, 1998 — first antennular segment with 5 setae (Itoh and Nishida 1998). 15. H. tamilensis (Thompson & A Scott, 1903) — female urosome 6-segmented (T Thompson and A Scott 1903). 16. H. thysanotus Wilson, 1935 — third exopodal segment of leg 4 with 9 (not 8) elements (Gooding 1960). 17. H. vicinalis Humes, 1995 — third exopodal segment of leg 4 with 9 elements (Humes 1995). 108 ZooKeys 1260: 93–109 (2025), DOI: 10.3897/zookeys.1260.168539 Il-Hoi Kim et al.: New Hemicyclops from a coral of the South China Sea Korzhavina O, Ivanenko V (2021) Global diversity and distributions of symbiotic copepod crustaceans living on hexacorallians. Version 1.7. Lomonosov Moscow State University. Occurrence dataset. https://doi.org/10.15468/heu2gx [accessed via GBIF.org on 2025-08-10] Lee J, Chang CY, Kim I-H (2022) Symbiotic copepods (Cyclopoida and Siphonostomatoida) collected by light trap from Korea. ZooKeys 1115: 1–71. https://doi.org/10.3897/ zookeys.1115.83266 Liu SYV, Green J, Briggs D, Hastings R, Jondelius Y, Kensinger S, Leever H, Santos S, Throne T, Cheng C, Madduppa H, Toonen RJ, Gaither MR, Crandall ED (2021) Dongsha Atoll is an important stepping-stone that promotes regional genetic connectivity in the South China Sea. PeerJ 9: e12063. https://doi.org/10.7717/peerj.12063 Moon SY, Kim I-H (2010) Three new species of Hemicyclops (Copepoda, Cyclopoida, Clausidiidae) from Korea. Animal Systematics, Evolution and Diversity 26(3): 279– 293. https://doi.org/10.5635/KJSZ.2010.26.3.279 Nicholls AG (1944) Littoral Copepoda from South Australia. II. Calanoida, Cyclopoida, Notodelphyoida, Monstrilloida and Caligoida. Records of the Australian Museum 8(1): 1–62. O’Reilly M (2000) The copepod Hemicyclops aberdonensis (Poecilostomatoida: Clausidiidae) and its suspected host the burrowing shrimp Calocaris macandreae in the Firth of Clyde. Glasgow Naturalist 23(5): 45–47. Ohtsuka S, Tomikawa K, Shang X (2010) A new species of Hemicyclops (Crustacea: Copepoda: Cyclopoida) found in plankton at the mouth of the Jiulong River, Southern China. Species Diversity : An International Journal for Taxonomy, Systematics, Speciation, Biogeography, and Life History Research of Animals 15(1): 41–50. https:// doi.org/10.12782/specdiv.15.41 Sars GO (1917) Copepoda Cyclopoida. Parts XI, XII. Clausidiidae, Lichomolgidae (part). An Account of the Crustacea of Norway, with short descriptions and figures of all the species. Bergen Museum, Bergen 6: 141–172. [pls 81–96] Scott T (1894) Report on Entomostraca from the Gulf of Guinea, collected by John Rattray, B.Sc. Transactions of the Linnean Society of London, Series 2, Zoology 6(1): 1–161. [pls 1–15] https://doi.org/10.1111/j.1096-3642.1894.tb00660.x Scott T, Scott A (1892) One new and rare Crustacea from the east coast of Scotland. The Annals of Scottish Natural History 31: 149–156. [pls 6, 7] https://doi.org/10.5962/ bhl.title.38007 Stock JH (1954) Redescription de Tococheres cylindraceus Pelseneer, 1929, copépode commensal de Loripes lacteus. Beaufortia 38(40): 73–80. Thompson IC, Scott A (1903) Report on the Copepoda collected by Professor Herdman, at Ceylon, in 1902. In: Herdman WA (Ed.) Report to the Government of Ceylon on the Pearl Oyster Fisheries of the Gulf of Manaar 1( suppl. 7): 227–307. [pls 1–20] https:// doi.org/10.5962/bhl.title.59334 Tkachenko KS, Soong K (2017) Dongsha Atoll: A potential thermal refuge for reef-building corals in the South China Sea. Marine Environmental Research 127: 112–125. https://doi.org/10.1016/j.marenvres.2017.04.003 Ummerkutty ANP (1962) Studies on Indian copepods. 5. On eleven new species of marine cyclopoid copepods from the south-east coast of India. Journal of the Marine Biological Association of India 3: 19–69. 109 ZooKeys 1260: 93–109 (2025), DOI: 10.3897/zookeys.1260.168539 Il-Hoi Kim et al.: New Hemicyclops from a coral of the South China Sea Vervoort W, Ramirez F (1966) Hemicyclops thalassius nov. spec. (Copepoda, Cyclopoida) from Mar del Plata, with revisionary notes on the family Clausidiidae. Zoologische Mededelingen, Leiden 41(13): 195–220. Walter C, Boxshall GA (2025) World of Copepods Database. Cyclopoida. Accessed through: World Register of Marine Species. http://www.marinespecies.org/aphia. php?p=taxdetails&id=1101 [accessed 30 July 2025] Supplementary material 1 Additional information Authors: Il-Hoi Kim, Jia Wang, Viatcheslav N. Ivanenko Data type: pdf Explanation note: fig. S1. Underwater photograph of the host coral Galaxea fascicularis prior to sampling. fig. S2. Underwater photograph of the dive computer at the sampling site. fig. S3. Photograph of the skeleton of the host coral Galaxea fascicularis. fig. S4. Macrophotograph of the skeleton of the host coral. fig. S5. Map of the atoll showing the sampling location (red mark), Google Maps. Copyright notice: This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited. Link: https://doi.org/10.3897/zookeys.1260.168539.suppl1