An Updated Checklist of Sea Slugs (Gastropoda, Heterobranchia) from Hong Kong Supported by Citizen Science

© 2022 Academia Sinica, Taiwan Open Access An Updated Checklist of Sea Slugs (Gastropoda, Heterobranchia) from Hong Kong Supported by Citizen Science Lai Him Chow1, Vriko Pik Fan Yu2,3,4, Zi Yi Kho1, Gomen Chun Lung See2,3, Adam Wang2,3, David M. Baker2,3 , and Ling Ming Tsang1,* 1Simon F. S. Li Marine Science Laboratory, School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong, China. *Correspondence: E-mail: [email protected] (Tsang). E-mail: [email protected] (Chow); [email protected] (Kho) 2The Swire Institute of Marine Science, The University of Hong Kong, Cape D’Aguilar Road, Shek O, Hong Kong, China. E-mail: [email protected] (Yu); [email protected] (Baker) 3School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China 4archiREEF Limited, Hong Kong Science and Technology Park, Shatin, Hong Kong, China Received 15 March 2022 / Accepted 15 June 2022 / Published 22 November 2022 Communicated by James D. Reimer Research on heterobranch sea slug diversity in Hong Kong was flourishing in the 1980–90s, with the first checklist and guidebook published and many new species and records documented later. This golden era of sea slug research ended abruptly, and no review nor any extensive collection has been done in the past 20+ years. In view of the extensive revision in heterobranch systematics in recent years, the current checklist can be considered out of date in both nomenclature and composition. Therefore, we are dedicated to providing a synthesis of the current state of knowledge on Hong Kong sea slug diversity by reviewing previous records and engagement of citizen science. An integration of previously published and unpublished records revealed the presence of 186 species, of which 107 species were documented by our citizen science programme with a further report of 71 new records. This yields a total of 257 species from 126 genera, 53 families and ten higher taxa, of which seven species have not been reported elsewhere from Hong Kong. While the present study has markedly illuminated our understanding of sea slug diversity in Hong Kong, the true biodiversity may be underestimated given the high proportion of novel records, especially when many previous records were not herein observed. Hong Kong likely harbours a greater sea slug diversity which awaits discovery from more rigorous sampling and a more inclusive citizen science programme. Key words: Biodiversity, Indo-West Pacific, Nudibranch, Opisthobranch, South China Sea. BACKGROUND The first account of sea slugs from Hong Kong was briefly mentioned in Collingwood (1881), where the author was accompanied by an experienced local in search for nudibranchs, but happened to be unsuccessful. Not until a century later was the first glimpse into the rich sea slug diversity available in the publication of checklists and guidebook in the 1980s (Orr 1980 1981; Tsi and Ma 1982; Britton 1984; Jensen 1985), courtesy of the late Dr. Brian Morton from The University of Hong Kong who organised a series of international workshops on Hong Kong and South China marine faunal and floral diversity and biology. These checklists collectively reported, as of old taxonomic classification, the presence of 91 species from 49 genera, 32 families and six orders (Anaspidea, Ascoglossa, Cephalaspidea, Notaspidea, Nudibranchia, Systellommatophora). Citation: Chow LH, Yu VPF, Kho ZY, See GCL, Wang A, Baker DM, Tsang LM. 2022. An updated checklist of sea slugs (Gastropoda, Heterobranchia) from Hong Kong supported by citizen science. Zool Stud 61:52. doi:10.6620/ZS.2022.61-52. Zoological Studies 61:52 (2022) doi:10.6620/ZS.2022.61-52 1 © 2022 Academia Sinica, Taiwan Nevertheless, some of the species reported were unidentified and their status will probably remain enigmatic due to the lack of vouchered specimens, clear colour photographs and/or detailed morphological descriptions. During the same period, Dr. Brian Darvell from The University of Hong Kong and other members from the South China Diving Club made an extensive collection of opisthobranch sea slugs from Hong Kong, later identified and studied by Dr. W. Bill Rudman from the Australian Museum. While over 230 species were collected, only a selection of 53 species from seven nudibranch families (Chromodorididae, Dorididae, Goniodorididae, Gymnodorididae, Myrrhinidae, Onchidorididae, Triophidae), together with materials from other places in the Indo-West Pacific, were detailed in a series of manuscripts, yielding 14 new species and 26 new records (Rudman 1982 1983 1985 1986a 1987a b 1990 1991; Rudman and Avern 1989; Rudman and Darvell 1990). In the following years, other researchers further contributed to the inventory of Hong Kong sea slug diversity with new species and records of nudibranch, cephalaspidean and sacoglossan, as well as the first record of acochlidiimorphan (Jensen 1990 1994 1997; Lin 1990a 1992; Hughes 1991). Jensen (1998) provided the latest checklist of opisthobranch containing 134 species from 72 genera and six orders (Acochlidiacea, Aplysiomorpha, Cephalaspidea, Notaspidea, Nudibranchia, Sacoglossa). This essentially marked the end of a golden era of sea slug research in Hong Kong with no further extensive collection performed since then. Sporadic new records were only mentioned and illustrated in guidebooks of Indo-Pacific sea slugs (Coleman 2008; Gosliner et al. 2008), many of which referred to unpublished materials mentioned in Rudman and Darvell (1990). In view of the extensive revision in heterobranch systematics in recent years (Bouchet et al. 2017) and range shifts attributed to climate change documented in many species (Nimbs and Smith 2018; Goddard et al. 2018), the current integrated checklist of heterobranch sea slugs can be considered out of date in both nomenclature and composition. It is, therefore, timely to conduct a review of sea slug diversity in Hong Kong and provide a synthesis of the current state of knowledge. Since sea slugs are distinctive in colouration and slow-moving, they are popular with underwater photographers. As such, a citizen science programme was initiated in summer 2020 through fall 2021, and aimed to document the occurrence of sea slugs in Hong Kong and collect photographic evidence on potential new records—a method that has shown to be effective in other places (Kleitou et al. 2019; Smith and Davis 2019). MATERIALS AND METHODS Previous records of heterobranch sea slugs from Hong Kong and their distribution were retrieved from various literatures and guidebooks, and from the website ‘The Sea Slug Forum’ (http://www.seaslugforum. net/) affiliated with the Australian Museum and maintained by sea slug taxonomist Dr. Bill Rudman. An online platform was established in summer 2020 and maintained through fall 2021 (for a total of 18 months) for citizen scientists to upload photographs of sea slugs taken in Hong Kong, both prior to and after the establishment of the citizen science programme. Citizen scientists were asked to provide sighting information, including date, location, water depth, and the substratum or organism the sea slug attached to. All species were identified from photographs only and no specimens were collected and examined in the present study. RESULTS A review and integration of previously published records of sea slugs in Hong Kong, and unpublished records from The Sea Slug Forum, revealed the presence of 186 species. Over 1400 photographs were received from 37 citizen scientists and the Agriculture, Fisheries and Conservation Department (AFCD), Hong Kong SAR Government, with the majority of the photographs taken within the past two years and the oldest photograph dated back to five years ago. This dataset contributed a total of 178 species, 71 of which were newly recorded in Hong Kong. This greatly expands the inventory of Hong Kong sea slug diversity, yielding a total of 257 species from 126 genera, 53 families and ten higher taxa (Table 1). The biodiversity is highly dominated by nudibranchs (181 species, 70.5%), followed by sacoglossans (30 species, 11.6%), cephalaspideans (18 species, 7.0%), aplysiidans (9 species, 3.5%), systellommatophores (7 species, 2.7%), pleurobranchs (6 species, 2.3%) and acteonimorphs (3 species, 1.2%) (Table 1). Only one species is recorded for acochlidiimorph, ringiculimorph, and umbraculidan. Fifty-four of the species are unidentified or tentatively identified (due to differences in colouration, anatomy or distribution, or insufficient information for accurate identification), some of which may potentially represent species complexes or new species whose true identity remains obscure without morphological examination and molecular analysis. For one of the species, Melibe cf. japonica, which is considered an uncertain synonym of Melibe viridis, we decided to retain the use of the name given its much less ornamented body. Another two species are considered inquirendum (cephalaspidean page 2 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan Philine vitrea (Philinidae), sacoglossan Placida daguilarensis (Limapontiidae)), but are still included in the present checklist as cross-references. DISCUSSION While Rudman and Darvell (1990) mentioned collecting over 230 species of opisthobranch sea slugs from Hong Kong, our review showed that past published and unpublished records only accounted for (not exclusively to opisthobranchs) a total of 186 species. This shows that our knowledge on Hong Kong sea slug diversity is very superficial and full of known unknowns. In other words, while a high diversity is recognised, only a portion of it is currently known with details. Greater sampling efforts are, therefore, required to supplement the recognised diversity. Citizen science is herein shown to be effective in documenting sea slug occurrence and discovering new records. Nearly 70% of the species in the checklist were documented in the present study, and > 25% of the species were new to Hong Kong. Compared to other subtropical regions in the Indo-Pacific with a similarly long (if not longer) history of research on sea slugs, Hong Kong is considered to have a relatively high sea slug diversity according to the present study, especially given its much smaller territorial area. For instance, 95 species have been reported from the Gujarat coast, India (Vadher et al. 2020), 105 species from Mauritius (Ah-Shee-Tee et al. 2019), 336 species from Thailand (256 species from the Gulf of Thailand alone) (Mehrotra et al. 2021), 382 species from the coast of New South Wales, Australia (Nimbs and Smith 2016), and 782 species from Taiwan (Chang 2012). The high diversity is possibly attributed Table 1. Number of sea slug species and genus recorded in Hong Kong under each family and higher taxon. *, total number under the higher taxon Taxa Species (Genus) Taxa Species (Genus) Acteonimorpha 3* (3)* Dendrodorididae 8 (2) Acteonidae 1 (1) Phyllidiidae 5 (3) Aplustridae 2 (2) Polyceridae 19 (8) Nudibranchia 181* (84)* Pleurobranchida 6* (4)* Aeolidiidae 10 (6) Pleurobranchaeidae 3 (2) Facelinidae 9 (6) Pleurobranchidae 3 (2) Myrrhinidae 3 (2) Ringiculimorpha 1* (1)* Arminidae 10 (2) Ringiculidae 1 (1) Bornellidae 1 (1) Acochlidiimorpha 1* (1)* Dotidae 3 (1) Pseudunelidae 1 (1) Lomanotidae 2 (1) Aplysiida 9* (3)* Scyllaeidae 1 (1) Aplysiidae 9 (3) Tethydidae 1 (1) Cephalaspidea 18* (13)* Abronicidae 1 (1) Bullidae 1 (1) Flabellinidae 2 (2) Cylichnidae 1 (1) Embletoniidae 1 (1) Haminoeidae 2 (2) Eubranchidae 2 (1) Aglajidae 8 (4) Pseudovermidae 1 (1) Gastropteridae 2 (2) Samlidae 1 (1) Philinidae 3 (2) Trinchesiidae 10 (3) Philinoglossidae 1 (1) Unidentiidae 1 (1) Systellommatophora 7* (6)* Madrellidae 1 (1) Onchidiidae 7 (6) Tritoniidae 4 (3) Sacoglossa 30* (10)* Actinocyclidae 3 (2) Oxynoidae 2 (2) Cadlinellidae 1 (1) Volvatellidae 1 (1) Chromodorididae 36 (11) Costasiellidae 3 (1) Hexabranchidae 1 (1) Limapontiidae 9 (3) Discodorididae 21 (11) Plakobranchidae 14 (2) Dorididae 4 (3) Platyhedylidae 1 (1) Aegiridae 2 (1) Umbraculida 1* (1)* Calycidorididae 1 (1) Umbraculidae 1 (1) Goniodorididae 16 (4) page 3 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan to range overlap of regional fauna (which also explains the very high diversity in Taiwan), including those from the South China Sea, Japanese and East Australian waters, as well as from the Indian Ocean and central Pacific. Of the species with confirmed identities, the majority of them have broad distribution throughout the Indo-Pacific or Indo-West Pacific (52.9%), typically ranging from the Red Sea, East and South Africa to the central Pacific islands to the east, Japan and Korea to the north, and Australia to the south, with a few additional species extending further westward into the Mediterranean Sea and eastern Atlantic, eastward to the eastern Pacific and western Atlantic, or even having a circum-tropical/temperate distribution (e.g., the acteonimorph Hydatina physis, the aplysiidan Bursatella leachii and the sacoglossan Ercolania coerulea). Two-fifths of the species are restricted to the western and central Pacific, of which five of the nudibranchs (Armina punctulata (Arminidae), Pseudovermis chinensis (Pseudovermidae), Phestilla fuscostriata (Trinchesiidae), Marionia echinomuriceae (Tritoniidae) and Lamellana gymnota (Polyceridae)), one of the cephalaspideans (Yokoyamaia orientalis (Philinidae)), and one of the sagoclossans (Gascoignella aprica (Platyhedylidae)), have not been reported elsewhere from Hong Kong. The validity of most of these species remains uncertain as they are known only from the original descriptions. The relatively recently described trinchesiid nudibranch P. fuscostriata is, nevertheless, expected to have a wider distribution given the commonness of its coral host in the Indo-Pacific (Hu et al. 2020a). The present study, based on a citizen science effort, provided the most comprehensive checklist of sea slugs in Hong Kong to date. While our understanding of their diversity has been markedly illuminated, the biodiversity revealed may still be an underestimate given the high proportion of novel records, especially when there was a lack of observation of many previous records. A greater biodiversity is likely to occur, and awaiting discovery from more extensive and systematic surveys of diverse habitats and water depths, and a more inclusive and long-term citizen science programme. Enriching the biodiversity database with substratum preference, local distribution and relative abundance information, as well as complementing observation with microscopic morphological examination and molecular analysis, would further foster a greater understanding of sea slugs in Hong Kong. Checklist of sea slugs from Hong Kong (HK) Species recorded in the present study are indicated by asterisk (*). Subclass Heterobranchia Infraclass Euthyneura Subterclass Acteonimorpha Superfamily Acteonoidea d'Orbigny, 1842 Family Acteonidae d'Orbigny, 1842 1. Pupa solidula (Linnaeus, 1758) Previous HK record: Lin and Qi (1985), Lin (1990b), Jensen (1998). Distribution: Indo-Pacific (from South Africa to Japan, New Caledonia and Fiji) (Coleman 2008). Family Aplustridae Gray, 1847 2. Bullina cf. nobilis Habe, 1950 Previous HK record: Jensen (2000). 3. Hydatina physis (Linnaeus, 1758)* (Fig. 1A) Previous HK record: None. Distribution: circum-tropical/temperate (Coleman 2008). Subterclass Ringipleura Superorder Nudipleura Order Nudibranchia Suborder Cladobranchia Superfamily Aeolidioidea Gray, 1827 Family Aeolidiidae Gray, 1827 4. Anteaeolidiella cf. fijiensis (Carmona, Bhave, Salunkhe, Pola, Gosliner & Cervera, 2014) Previous HK record: Orr (1981) (as Aeolidia cf. foulisi), Jensen (1998) (as Aeolidia cf. foulisi). 5. Anteaeolidiella cf. indica (Bergh, 1888) Previous HK record: Orr (1981) (as Aeolidiella sp.). 6. Anteaeolidiella lurana (Ev. Marcus & Er. Marcus, 1967)* (Fig. 1B) Previous HK record: Orr (1980 1981) (as Aeolidiella takanosimensis), Morton and Morton (1983) (as Aeolidiella takanosinensis), Jensen (1998) (as Aeolidiella indica). Distribution: western Pacific (Hong Kong, Australia), Mediterranean (Italy, Spain), Atlantic (Canary Islands, the Caribbean, Bermuda) (Carmona et al. 2014a). 7. Baeolidia cf. moebii Bergh, 1888 Previous HK record: Orr (1980) (as Aeolidiella cf. berghia), Orr (1981) (as Aeolidiella sp.). 8. Baeolidia salaamica (Rudman, 1982)* (Fig. 1C) Previous HK record: Orr (1980 1981) (as Berghia japonica), Jensen (1998) (as Berghia japonica). Distribution: Indo-Pacific (from East Africa to Japan, South Korea, the Philippines, Papua New Guinea and Hawaii) (Carmona et al. 2014b). page 4 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan 9. Bulbaeolidia alba (Risbec, 1928)* (Fig. 1D) Previous HK record: None. Distribution: Indo-Pacific (from East Africa to Japan, Australia, French Polynesia, Midway Atoll and Hawaii) (Tibirica et al. 2017). 10. Cerberilla ambonensis Bergh, 1905* (Fig. 1E) Previous HK record: Rudman (2001a) (as Cerberilla sp. 4). Distribution: western Pacific (from Thailand to Indonesia, Solomon Islands and Australia) (Mehrotra et al. 2021). 11. Cerberilla cf. incola Burn, 1974 Previous HK record: Rudman (2001a) (as Cerberilla sp. 4). 12. Limenandra fusiformis (Baba, 1949) Previous HK record: Tsi and Ma (1982), Jensen (1998). Distribution: Indo-Western Pacific (Hong Kong, Japan, the Red Sea) (Jensen 1998; Gosliner et al. 2008). 13. Spurilla braziliana MacFarland, 1909* (Fig. 1F) Previous HK record: Lin (1992) (as Aeolidiella albopunctata), Jensen (1998) (as Aeolidiella albopunctata), Gosliner et al. (2008) (as Spurilla neapolitana). Distribution: Pacific (from Hong Kong, Australia and Japan to Hawaii, and to Costa Rica and Peru) and western Atlantic (from Florida and Mexico to Brazil and Chile) (Carmona et al. 2014c). Family Facelinidae Bergh, 1889 14. Caloria indica (Bergh, 1896)* (Fig. 1G) Previous HK record: Coleman (2008), Gosliner et al. (2008). Distribution: Indo-Pacific (from East Africa to Fiji) (Mehrotra et al. 2021). 15. Cratena cf. poshitraensis Bharate, Padula, Apte & Shimpi, 2020* (Fig. 1H) Previous HK record: None. 16. Cratena sp.* (Fig. 1I) Previous HK record: None. 17. Facelina sp.* (Fig. 1J) Previous HK record: None. 18. Favorinus sp.* (Fig. 1K) Previous HK record: None. 19. Phidiana anulifera (Baba, 1949)* (Fig. 1L) Previous HK record: Rudman (2001b). Distribution: Indo-West Pacific (Hong Kong, India, Taiwan, Japan) (Gosliner 1979; Rudman 2001b). 20. Phidiana militaris (Alder & Hancock, 1864)* (Fig. 1M) Previous HK record: Coleman (2008). Distribution: Indo-West Pacific (from the Arabian Sea to Hong Kong, Taiwan and the Philippines) and eastern Mediterranean (Israel) (Mehrotra et al. 2021). 21. Sakuraeolis enosimensis (Baba, 1930)* (Fig. 1N) Previous HK record: Orr (1981) (as Coryphella sp.), Morton and Morton (1983), Jensen (1998). Distribution: western Pacific (Hong Kong, Japan), introduced to eastern Pacific (California) (Behrens 1982; Jensen 1998). 22. Sakuraeolis sp.* (Fig. 1O) Previous HK record: None. Family Myrrhinidae Bergh, 1905 23. Godiva cf. rachelae Rudman, 1980* (Fig. 1P) Previous HK record: None. 24. Phyllodesmium magnum Rudman, 1991* (Fig. 1Q) Previous HK record: Orr (1980 1981) (as Phyllodesmium sp.), Rudman (1991), Jensen (1998), Coleman (2008), Gosliner et al. (2008). Distribution: western Pacific (Hong Kong, Taiwan, Malaysia, the Philippines, Australia, Japan) (Mehrotra et al. 2021). 25. Phyllodesmium opalescens Rudman, 1991* (Fig. 1R) Previous HK record: Rudman (1991), Jensen (1998), Gosliner et al. (2008). Distribution: western Pacific (Hong Kong, Taiwan, the Philippines) (Min 2004; Mehrotra et al. 2021). Superfamily Arminoidea Iredale & O'Donoghue, 1923 (1841) Family Arminidae Iredale & O'Donoghue, 1923 (1841) 26. Armina cf. babai (Tchang, 1934) Previous HK record: Jensen (1997 1998). 27. Armina comta (Bergh, 1880) Previous HK record: Orr (1980 1981) (as Armina japonica), Tsi and Ma (1982), Morton and Morton (1983) (as Armina japonica), Jensen (1997 1998). Distribution: western Pacific (Hong Kong, Thailand, Japan) (Jensen 1998). 28. Armina papillata Baba, 1933 Previous HK record: Tsi and Ma (1982), Jensen (1997 1998). Distribution: western Pacific (Hong Kong, Taiwan, Australia, Japan) (Tsi and Ma 1982; Jensen 1998; Nimbs and Smith 2016). 29. Armina punctilopsis Lin, 1992 Previous HK record: Lin (1992), Jensen (1998). Distribution: Indo-West Pacific (Hong Kong, Pakistan) (Kazmi et al. 1996). 30. Armina punctulata Lin, 1990 page 5 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan Fig. 1. (A) Hydatina physis; (B) Anteaeolidiella lurana; (C) Baeolidia salaamica; (D) Bulbaeolidia alba; (E) Cerberilla ambonensis; (F) Spurilla braziliana; (G) Caloria indica; (H) Cratena cf. poshitraensis; (I) Cratena sp.; (J) Facelina sp.; (K) Favorinus sp.; (L) Phidiana anulifera; (M) Phidiana militaris; (N) Sakuraeolis enosimensis; (O) Sakuraeolis sp.; (P) Godiva cf. rachelae; (Q) Phyllodesmium magnum; (R) Phyllodesmium opalescens. Photographs by Harmon Wong (A), Tim Lam (B–D, G–I, K, L, P, R), Rachel Wong (E), AFCD (F, Q), Henry Li (J), Caron Ka Lok Wong (M), Gary To (N) and Alice Au (O). page 6 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan Previous HK record: Lin (1990a), Jensen (1997 1998). Distribution: Hong Kong (Jensen 1998). 31. Armina variolosa (Bergh, 1904) Previous HK record: Jensen (1997 1998), Coleman (2008), Gosliner et al. (2018). Distribution: western Pacific (China, Japan) (Jensen 1998). 32. Dermatobranchus albus (Eliot, 1904)* (Fig. 2A) Previous HK record: None. Distribution: Indo-West Pacific (from East Africa to Japan and Papua New Guinea) (Gosliner and Fahey 2011). 33. Dermatobranchus tongshanensis Lin, 1981* (Fig. 2B) Previous HK record: Jensen (2000). Distribution: western Pacific (China) (Lin 1981). 34. Dermatobranchus sp. 1* (Fig. 2C) Previous HK record: None. 35. Dermatobranchus sp. 2* (Fig. 2D) Previous HK record: None. Superfamily Dendronotoidea Allman, 1845 Family Bornellidae Bergh, 1874 36. Bornella stellifera (Adams & Reeve [in Adams], 1848)* (Fig. 2E) Previous HK record: Orr (1980 1981), Morton and Morton (1983), Lin (1990b), Jensen (1998). Distribution: Indo-Pacific (from South Africa to New Caledonia, Fiji and Japan) (Mehrotra et al. 2021). Family Dotidae Gray, 1853 37. Doto sp. 1 Previous HK record: Gosliner et al. (2008 2018). 38. Doto sp. 2* (Fig. 2F) Previous HK record: None. 39. Doto sp. 3* (Fig. 2G, H) Previous HK record: None. Family Lomanotidae Bergh, 1890 40. Lomanotus vermiformis Eliot, 1908* (Fig. 2I) Previous HK record: None. Distribution: Indo-Pacific (from the Red Sea to Taiwan, Australia and Fiji, and to Panama), and western Atlantic (Florida, Caribbean Sea) (Mehrotra et al. 2021). 41. Lomanotus sp.* (Fig. 2J) Previous HK record: None. Family Scyllaeidae Alder & Hancock, 1855 42. Notobryon wardi Odhner, 1936* (Fig. 2K) Previous HK record: Picton (2002), Coleman (2008). Distribution: western and central Pacific (Hong Kong, Japan, South Korea, Northern Mariana Islands, Marshall Islands, the Philippines, Indonesia, Australia, Hawaii) (Pola et al. 2012). Family Tethydidae Rafinesque, 1815 43. Melibe cf. japonica Eliot, 1913 (uncertain synonym of M. viridis)* (Fig. 2L) Previous HK record: None. Superfamily Fionoidea Gray, 1857 Family Abronicidae Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, Saito, Lundin, Schrödl & Picton, 2017 44. Abronica purpureoanulata (Baba, 1961)* (Fig. 2M) Previous HK record: Orr (1980 1981) (as Catriona cf. purpureoanulata), Jensen (1998) (as Catriona cf. purpureoanulata), Gosliner et al. (2008). Distribution: western Pacific (Hong Kong, the Philippines, Japan) (Jensen 1998; Anderson 2008). Family Flabellinidae Bergh, 1889 45. Coryphellina lotos Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, Saito, Lundin, Schrödl & Picton, 2017* (Fig. 2N) Previous HK record: None. Distribution: western Pacific (Hong Kong, Japan). (Mehrotra et al. 2021). 46. Flabellina sp.* (Fig. 2O) Previous HK record: None. Family Embletoniidae Pruvot-Fol, 1954 47. Embletonia gracilis Risbec, 1928 Previous HK record: Hughes (1991) (as Embletonia pulchra), Jensen (1998) (as Embletonia pulchra). Distribution: Indo-Pacific (from Christmas Island to Japan, Fiji and Hawaii) (Miller and Willan 1992; Jensen 1998). Family Eubranchidae Odhner, 1934 48. Eubranchus inabai Baba, 1964 Previous HK record: Gosliner et al. (2008). Distribution: western Pacific (Hong Kong, Taiwan, page 7 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan Fig. 2. (A) Dermatobranchus albus; (B) Dermatobranchus tongshanensis; (C) Dermatobranchus sp. 1; (D) Dermatobranchus sp. 2; (E) Bornella stellifera; (F) Doto sp. 2; (G, H) Doto sp. 3; (I) Lomanotus vermiformis; (J) Lomanotus sp.; (K) Notobryon wardi; (L) Melibe cf. japonica; (M) Abronica purpureoanulata; (N) Coryphellina lotos; (O) Flabellina sp.; (P) Eubranchus rubropunctatus; (Q) Samla bicolor; (R) Catriona pinnifera. Photographs by Tim Lam (A–E, G, I, L, M, R), AFCD (F, H, P), Alice Au (J), Tom Chan (K), Gary To (N), AFCD | Henry Tat Heng Ho (O), Henry Li (P) and Markus Rummel (Q). page 8 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan Australia, Japan) (Baba 1964; Nimbs and Smith 2016). 49. Eubranchus rubropunctatus Edmunds, 1969* (Fig. 2P) Previous HK record: Picton (2001) (as Eubranchus cf. rubropunctatus), Gosliner et al. (2008) (as Eubranchus sp. 1). Distribution: western Pacific (Hong Kong, Australia) (Marshall and Willan 1999; Gosliner et al. 2008). Family Pseudovermidae Thiele, 1931 50. Pseudovermis chinensis Hughes, 1991 Previous HK record: Hughes (1991), Jensen (1998). Distribution: Hong Kong (Jensen 1998). Family Samlidae Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, Saito, Lundin, Schrödl & Picton, 2017 51. Samla bicolor (Kelaart, 1858)* (Fig. 2Q) Previous HK record: Orr (1980 1981) (as Flabellina ornata), Jensen (1998), Coleman (2008), Gosliner et al. (2008). Distribution: Indo-Pacific (from South Africa to Japan, South Korea, Tonga and Hawaii) (Mehrotra et al. 2021). Family Trinchesiidae Nordsieck, 1972 52. Catriona pinnifera (Baba, 1949)* (Fig. 2R) Previous HK record: None. Distribution: western and central Pacific (Hong Kong, Japan, Hawaii) (Baba 1961; Gosliner 1979; Present study). 53. Phestilla fuscostriata Hu, Zhang, Xie & Qiu, 2020* (Fig. 3A) Previous HK record: Wong et al. (2017) (as Tenellia sp.), Hu et al. (2020a). Distribution: western Pacific (Hong Kong, Thailand) (Mehrotra et al. 2021). 54. Phestilla goniophaga Hu, Zhang, Yiu, Xie & Qui, 2020* (Fig. 3B) Previous HK record: Orr (1981) (as Phestilla sp.), Coleman (2008) (as Phestilla sp.), Gosliner et al. (2008) (as Phestilla sp.), Hu et al. (2020b). Distribution: western Pacific (Hong Kong, Palau) (Hu et al. 2020b). 55. Phestilla lugubris (Bergh, 1870)* (Fig. 3C) Previous HK record: Orr (1980) (as Phestilla sibogae), Morton and Morton (1983) (as Phestilla sibogae), Jensen (1998) (as Phestilla sibogae). Distribution: Indo-Pacific (from East Africa to New Caledonia and Hawaii) (Mehrotra et al. 2021). 56. Phestilla melanobrachia Bergh, 1874* (Fig. 3D, E) Previous HK record: Orr (1981), Morton and Morton (1983), Jensen (1998), Gosliner et al. (2008). Distribution: Indo-Pacific (from East Africa to Japan, Australia, Soloman Islands and Fiji) (Mehrotra et al. 2021). 57. Phestilla sp.* (Fig. 3F) Previous HK record: None. 58. Trinchesia diversicolor Baba, 1975 Previous HK record: Orr (1981) (as Trinchesia sp.), Gosliner et al. (2008). Distribution: western Pacific (Hong Kong, Taiwan, Japan, South Korea) (Baba 1975; Min 2004; Jie and Chan 2009). 59. Trinchesia ornata (Baba, 1937)* (Fig. 3G) Previous HK record: Orr (1980) (as Trinchesia cf. ornata), Jensen (1998) (as Trinchesia cf. ornata), Coleman (2008), Gosliner et al. (2008). Distribution: Indo-West Pacific (from South Africa to Russia and Australia) (Nimbs et al. 2016). 60. Trinchesia yamasui (Hamatani, 1993)* (Fig. 3H) Previous HK record: None. Distribution: Indo-Pacific (from the Red sea to Japan, Australia and Marshall Islands) (Hamatani 1993; Yonow 2015; Nimbs and Smith 2016). 61. Trinchesia sp.* (Fig. 3I) Previous HK record: None. Family Unidentiidae Millen & Hermosillo, 2012 62. Unidentia aliciae Korshunova, Mehrotra, Arnold, Lundin, Picton & Martynov, 2019* (Fig. 3J) Previous HK record: None. Distribution: western Pacific (Hong Kong, Thailand) (Mehrotra et al. 2021). Superfamily Proctonotoidea Gray, 1853 Family Madrellidae Preston, 1911 63. Madrella ferruginosa Alder & Hancock, 1864* (Fig. 3K) Previous HK record: None. Distribution: Indo-Pacific (from East Africa to Japan, Australia, New Caledonia, Marshall Islands) (Gosliner and Fahey 2011). Superfamily Tritonioidea Lamarck, 1809 Family Tritoniidae Lamarck, 1809 64. Marionia echinomuriceae Jensen, 1994* (Fig. 3L) Previous HK record: Jensen (1994 1998). Distribution: Hong Kong (Jensen 1998). page 9 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan Fig. 5. (A) Ceratosoma trilobatum; (B) Hypselodoris apolegma; (C) Hypselodoris confetti; (D) Hypselodoris decorata; (E) Hypselodoris festiva; (F) Hypselodoris katherinae; (G) Hypselodoris maritima; (H) Hypselodoris placida; (I) Mexichromis multituberculata; (J) Mexichromis similaris; (K) Thorunna florens; (L) Atagema intecta; (M) Atagema spongiosa; (N) Atagema sp.; (O) Carminodoris pustulata; (P) Jorunna parva; (Q) Jorunna cf. ramicola; (R) Platydoris ellioti. Photographs by Tim Lam (A, C, D, F, H–J, L–Q), AFCD | Wai Hong Yiu (B), Sze Yiu Ng (E, G), Alice Au (K) and Caron Ka Lok Wong (R). page 16 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan Gosliner 2004; Coleman 2008). 135. Aegires villosus Farran, 1905* (Fig. 6H) Previous HK record: None. Distribution: Indo-Pacific (From India to Japan, Australia, New Caledonia and Tonga) (Fahey and Gosliner 2004). Family Calycidorididae Roginskaya, 1972 136. Diaphorodoris mitsuii (Baba, 1938)* (Fig. 6I) Previous HK record: Rudman and Darvell (1990), Jensen (1998), Coleman (2008), Gosliner et al. (2008). Distribution: western Pacific (Hong Kong, Taiwan, Japan, South Korea, Papua New Guinea, Australia) (Coleman 2008; Jie and Chan 2009). Family Goniodorididae H. Adams & A. Adams, 1854 137. Goniodoridella savignyi Pruvot-Fol, 1933* (Fig. 6J) Previous HK record: Rudman and Darvell (1990), Jensen (1998). Distribution: Indo-West Pacific (from East Africa to Japan, South Korea, Russia and Australia) (Coleman 2008). 138. Goniodoris cf. castanea Alder & Hancock, 1845 Previous HK record: Rudman and Darvell (1990), Jensen (1998). 139. Goniodoris felis Baba, 1949* (Fig. 6K) Previous HK record: Rudman and Darvell (1990), Jensen (1998), Gosliner et al. (2008). Distribution: western Pacific (Hong Kong, Taiwan, Japan, South Korea, possibly the Philippines) (Coleman 2008). 140. Goniodoris joubini Risbec, 1928 Previous HK record: Orr (1980 1981), Morton and Morton (1983) (as Goniodoris glabrata), Rudman and Darvell (1990), Jensen (1998), Coleman (2008), Gosliner et al. (2008). Distribution: Indo-Pacific (from the Red Sea to Japan, Australia, New Caledonia and Marshall Islands) (Coleman 2008). 141. Goniodoris sp.* (Fig. 6L) Previous HK record: None. 142. Okenia barnardi Baba, 1937* (Fig. 6M) Previous HK record: Rudman and Darvell (1990), Jensen (1998), Rudman (2004). Distribution: western Pacific (Hong Kong, Taiwan, Japan, South Korea) (Rudman 2004; Chang 2012). 143. Okenia hiroi (Baba, 1938)* (Fig. 6N) Previous HK record: Rudman and Darvell (1990), Jensen (1998), Rudman (2004), Coleman (2008). Distribution: western Pacific (Hong Kong, Japan, South Korea) (Jung et al. 2014). 144. Okenia japonica Baba, 1949* (Fig. 6O) Previous HK record: Rudman and Darvell (1990), Jensen (1998), Rudman (2004), Gosliner et al. (2008 2018). Distribution: western Pacific (Hong Kong, Taiwan, Japan, the Philippines) (Rudman 2004; Anderson 2008; Jie and Chan 2009). 145. Okenia pilosa (Bouchet & Ortea, 1983)* (Fig. 6P) Previous HK record: Rudman and Darvell (1990), Jensen (1998), Rudman (2004), Gosliner et al. (2008). Distribution: Indo-West Pacific (Hong Kong, Japan, Papua New Guinea, Australia, New Caledonia, India) (Rudman 2004). 146. Okenia plana Baba, 1960* (Fig. 6Q) Previous HK record: Rudman and Darvell (1990), Jensen (1998), Rudman (2004), Gosliner et al. (2008). Distribution: western Pacific (Hong Kong, Japan, the Philippines, Australia, New Zealand), introduced to eastern Pacific (California) (Rudman 2004). 147. Okenia sp.* (Fig. 6R) Previous HK record: None. 148. Trapania aurata Rudman, 1987* (Fig. 7A) Previous HK record: Rudman (1987b), Rudman and Darvell (1990), Jensen (1998), Coleman (2008), Gosliner et al. (2008 2018). Distribution: western Pacific (Hong Kong, Australia, New Caledonia) (Coleman 2008). 149. Trapania darvelli Rudman, 1987* (Fig. 7B) Previous HK record: Rudman (1987b), Rudman and Darvell (1990), Jensen (1998), Coleman (2008), Gosliner et al. (2008). Distribution: western and central Pacific (Hong Kong, Taiwan, Malaysia, Solomon Islands, Marshall Islands) (Coleman 2008). 150. Trapania japonica (Baba, 1935)* (Fig. 7C) Previous HK record: Rudman (1987b), Rudman and Darvell (1990), Jensen (1998). Distribution: western Pacific (Hong Kong, Indonesia, Australia, Japan) (Jensen 1998). 151. Trapania miltabrancha Gosliner & Fahey, 2008* (Fig. 7D) Previous HK record: None. Distribution: western Pacific (Hong Kong, Thailand, Indonesia, Japan) (Mehrotra et al. 2021). 152. Trapania toddi Rudman, 1987 Previous HK record: Rudman (1987b), Rudman and Darvell (1990), Jensen (1998), Coleman (2008), Gosliner et al. (2008 2018). Distribution: Indo-West Pacific (from the Red Sea page 17 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan Fig. 6. (A) Rostanga bifurcata; (B) Rostanga dentacus; (C) Sclerodoris apiculata; (D) Doriopsis granulosa; (E) Doris sp.; (F) Homoiodoris japonica; (G) Aegires exeches; (H) Aegires villosus; (I) Diaphorodoris mitsuii; (J) Goniodoridella savignyi; (K) Goniodoris felis; (L) Goniodoris sp.; (M) Okenia barnardi; (N) Okenia hiroi; (O) Okenia japonica; (P) Okenia pilosa; (Q) Okenia plana; (R) Okenia sp. Photographs by Tim Lam (A–G, I– M, O–R), Grape Tang (H) and Gary To (N). page 18 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan to Japan, South Korea and Australia) (Coleman 2008). Superfamily Phyllidioidea Rafinesque, 1814 Family Dendrodorididae O'Donoghue, 1924 (1864) 153. Dendrodoris arborescens (Collingwood, 1881)* (Fig. 7E) Previous HK record: Brodie et al. (1997) (as Dendrodoris fumata (black form)). Distribution: Indo-West Pacific (Hong Kong, Japan, Australia) (Debelius and Kuiter 2007). 154. Dendrodoris fumata (Rüppell & Leuckart, 1830)* (Fig. 7F, G) Previous HK record: Orr (1980 1981), Morton and Morton (1983), Brodie et al. (1997), Jensen (1998), Coleman (2008). Distribution: Indo-Pacific (from East Africa and Christmas Island to Japan, South Korea, Australia, New Caledonia and Fiji) (Mehrotra et al. 2021). 155. Dendrodoris guttata (Odhner, 1917) Previous HK record: Orr (1980 1981), Morton and Morton (1983), Jensen (1998), Coleman (2008). Distribution: Indo-West Pacific (from Andaman Islands to Australia, Japan and South Korea) (Coleman 2008). 156. Dendrodoris krusensternii (Gray, 1850)* (Fig. 7H) Previous HK record: Orr (1980 1981), Morton and Morton (1983), Lin (1990b), Jensen (1998). Distribution: Indo-Pacific (from East Africa to Japan, South Korea, Australia, New Zealand, New Caledonia, Fiji and Hawaii) (Tibirica et al. 2017). 157. Dendrodoris nigra (Stimpson, 1855)* (Fig. 7I, J) Previous HK record: Orr (1980 1981), Lin (1990b), Brodie et al. (1997), Jensen (1998). Distribution: Indo-Pacific (from East Africa and Christmas Island to Australia, New Zealand, New Caledonia and Fiji) (Mehrotra et al. 2021). 158. Dendrodoris tuberculosa (Quoy & Gaimard, 1832) Previous HK record: Rudman (2007), Coleman (2008). Distribution: Indo-Pacific (from East Africa to Japan, South Korea, Australia, Solomon Islands and Fiji) (Mehrotra et al. 2021). 159. Dendrodoris sp.* (Fig. 7K) Previous HK record: None. 160. Doriopsilla miniata (Alder & Hancock, 1864)* (Fig. 7L) Previous HK record: Orr (1980 1981), Morton and Morton (1983) (as Doriopsilla areolata), Jensen (1998), Coleman (2008). Distribution: Indo-West Pacific (Hong Kong, Japan, Australia, India, South Africa) (Coleman 2008). Family Phyllidiidae Rafinesque, 1814 161. Phyllidia ocellata Cuvier, 1804* (Fig. 7M) Previous HK record: Rudman and Darvell (2001), Coleman (2008). Distribution: Indo-Pacific (from East Africa to Japan, South Korea, Australia, Solomon Islands, Fiji and Marshall Islands) (Mehrotra et al. 2021). 162. Phyllidia picta Pruvot-Fol, 1957 Previous HK record: Orr (1980 1981) (as Phyllidia varicosa), Coleman (2008), Gosliner et al. (2008). Distribution: Indo-Pacific (from the Arabian Sea to Japan, South Korea, Australia, Solomon Islands, Vanuatu and Fiji) (Mehrotra et al. 2021). 163. Phyllidia varicosa Lamarck, 1801* (Fig. 7N) Previous HK record: Morton and Morton (1983), Lin (1990b), Jensen (1998). Distribution: Indo-Pacific (from East Africa and Maldives to Japan, Guam, Australia, New Caledonia and Fiji) (Mehrotra et al. 2021). 164. Phyllidiella pustulosa (Cuvier, 1804)* (Fig. 7O) Previous HK record: Orr (1980 1981) (as Phyllidia sp.), Tsi and Ma (1982), Jensen (1998). Distribution: Indo-Pacific (from the Red Sea to Japan, Guam, Australia, Line Islands, Tuamotu Islands and Hawaii) (Mehrotra et al. 2021). 165. Phyllidiopsis cardinalis Bergh, 1876* (Fig. 7P) Previous HK record: None. Distribution: Indo-Pacific (from East Africa to Japan, Guam, Australia, New Caledonia and Fiji) (Tibirica et al. 2017). Superfamily Polyceroidea Alder & Hancock, 1845 Family Polyceridae Alder & Hancock, 1845 Subfamily Kalinginae Pruvot-Fol, 1956 166. Kalinga ornata Alder & Hancock, 1864* (Fig. 7Q) Previous HK record: Rudman and Darvell (1990), Jensen (1998 2000). Distribution: Indo-Pacific (from East Africa to Australia, Japan and Hawaii) (Coleman 2008). Subfamily Nembrothinae Burn, 1967 167. Tambja cf. pulcherrima Willan & Chang, 2017* (Fig. 7R) Previous HK record: None. 168. Roboastra cf. tentaculata (Pola, Cervera & Gosliner, 2005)* (Fig. 8A) Previous HK record: None. page 19 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan Fig. 7. (A) Trapania aurata; (B) Trapania darvelli; (C) Trapania japonica; (D) Trapania miltabrancha; (E) Dendrodoris arborescens; (F, G) Dendrodoris fumata; (H) Dendrodoris krusensternii; (I, J) Dendrodoris nigra; (K) Dendrodoris sp.; (L) Doriopsilla miniata; (M) Phyllidia ocellata; (N) Phyllidia varicosa; (O) Phyllidiella pustulosa; (P) Phyllidiopsis cardinalis; (Q) Kalinga ornata; (R) Tambja cf. pulcherrima; Photographs by Tim Lam (A–C, G, K, N, Q, R), Dik Cheung (D), Sze Yiu Ng (E), AFCD (F, J, M, P) and Gomen See (H, I, L, O). page 20 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan Subfamily Polycerinae Alder & Hancock, 1845 169. Gymnodoris alba (Bergh, 1877)* (Fig. 8B) Previous HK record: Rudman and Darvell (1990), Jensen (1998). Distribution: Indo-Pacific (from East Africa to Australia, Japan and Hawaii) (Mehrotra et al. 2021). 170. Gymnodoris amakusana (Baba, 1996)* (Fig. 8C) Previous HK record: Rudman and Darvell (1990) (as Gymnodoris striata), Coleman (2008). Distribution: western Pacific (Hong Kong, Taiwan, Japan, Australia, New Caledonia) (Coleman 2008). 171. Gymnodoris citrina (Bergh, 1877)* (Fig. 8D) Previous HK record: Orr (1980 1981), Morton and Morton (1983), Rudman and Darvell (1990), Jensen (1998), Coleman (2008) (as Gymnodoris bicolor). Distribution: Indo-Pacific (from East Africa to Japan, Australia and Samoa) (Tibirica et al. 2017). 172. Gymnodoris impudica (Rüppell & Leuckart, 1830)* (Fig. 8E) Previous HK record: Rudman and Darvell (1990), Jensen (1998), Coleman (2008). Distribution: Indo-West Pacific (from East Africa to Japan, Solomon Islands, Australia and New Caledonia) (Mehrotra et al. 2021). 173. Gymnodoris inornata (Bergh, 1880)* (Fig. 8F) Previous HK record: Orr (1980 1981), Lin (1990b), Rudman and Darvell (1990), Jensen (1998), Coleman (2008), Gosliner et al. (2008). Distribution: Indo-West Pacific (from South Africa to Japan, Australia and New Caledonia) (Mehrotra et al. 2021). 174. Gymnodoris nigricolor Baba, 1960* (Fig. 8G) Previous HK record: Tsi and Ma (1982), Rudman and Darvell (1990) (as Gymnodoris cf. nigricolor), Jensen (1998) (as Cratena nigricolor). Distribution: Indo-West Pacific (Hong Kong, Japan, Solomon Islands, the Red Sea) (Coleman 2008; Mehrotra et al. 2021). 175. Gymnodoris plebeia (Bergh, 1877) Previous HK record: Coleman (2008). Distribution: western and central Pacific (Hong Kong, Japan, New Caledonia, Marshall Islands, Hawaii) (Kay and Young 1969; Coleman 2008). 176. Gymnodoris subflava Baba, 1949 Previous HK record: Rudman and Darvell (1990), Jensen (1998). Distribution: Indo-West Pacific (from Andaman Islands to Hong Kong, the Philippines and Japan) (Jensen 1998; Debelius and Kuiter 2007). 177. Gymnodoris sp.* (Fig. 8H) Previous HK record: Rudman and Darvell (1990). 178. Lamellana gymnota Lin, 1992 Previous HK record: Lin (1992), Jensen (1998). Distribution: Hong Kong (Jensen 1998). 179. Polycera fujitai Baba, 1937* (Fig. 8I) Previous HK record: Orr (1980 1981), Morton and Morton (1983), Jensen (1998). Distribution: western Pacific (Hong Kong, Japan, New Zealand) (Jensen 1998; Miller 2001). 180. Polycera sp.* (Fig. 8J) Previous HK record: None. Subfamily Triophinae Odhner, 1941 181. Kaloplocamus acutus Baba, 1949* (Fig. 8K) Previous HK record: Rudman and Darvell (1990), Jensen (1998), Coleman (2008), Gosliner et al. (2008). Distribution: Indo-Pacific (from Andaman Islands to Japan, South Korea, Australia, New Caledonia and Hawaii) (Coleman 2008). 182. Kaloplocamus ramosus (Cantraine, 1835)* (Fig. 8L) Previous HK record: Rudman and Darvell (1990) (as Kaloplocamus cf. ramosus), Jensen (1998) (as Kaloplocamus cf. ramosus), Jensen (2000), Gosliner et al. (2008). Distribution: Indo-Pacific (from South Africa to Japan, South Korea, Australia and Hawaii), Mediterranean (Adriatic Sea), and eastern Atlantic (West Africa, Azores, Bay of Biscay) (Coleman 2008). 183. Plocamopherus ceylonicus (Kelaart, 1858)* (Fig. 8M) Previous HK record: Rudman and Darvell (1990), Jensen (1998 2000), Coleman (2008), Gosliner et al. (2008). Distribution: Indo-Pacific (from East Africa to Japan, Australia, New Caledonia and Marshall Islands) (Coleman 2008). 184. Plocamopherus tilesii Bergh, 1877* (Fig. 8N) Previous HK record: Rudman and Darvell (1990), Jensen (1998 2000). Distribution: Indo-West Pacific (from the Arabian Sea to Japan, South Korea and Australia) and eastern Mediterranean (Turkey) (Mehrotra et al. 2021). Order Pleurobranchida Superfamily Pleurobranchoidea Gray, 1827 Family Pleurobranchaeidae Pilsbry, 1896 185. Euselenops luniceps (Cuvier, 1816) Previous HK record: Tsi and Ma (1982), Jensen (1994 1998), Coleman (2008). Distribution: Indo-West Pacific (from East Africa page 21 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan Fig. 8. (A) Roboastra cf. tentaculata; (B) Gymnodoris alba; (C) Gymnodoris amakusana; (D) Gymnodoris citrina; (E) Gymnodoris impudica; (F) Gymnodoris inornata; (G) Gymnodoris nigricolor; (H) Gymnodoris sp.; (I) Polycera fujitai; (J) Polycera sp.; (K) Kaloplocamus acutus; (L) Kaloplocamus ramosus; (M) Plocamopherus ceylonicus; (N) Plocamopherus tilesii; (O) Pleurobranchaea brockii; (P) Berthellina citrina; (Q) Pleurobranchus forskalii; (R) Pleurobranchus peronii. Photographs by Tim Lam (A, C, F–H, L, M, O, P), AFCD (B, E, Q), Sze Yiu Ng (D, K), WK Chow (I), Gomen See (J, N) and Wai Hong Yiu (R). page 22 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan to Australia and Japan) (Coleman 2008). 186. Pleurobranchaea brockii Bergh, 1897* (Fig. 8O) Previous HK record: Tsi and Ma (1982), Lin (1990b), Jensen (1994 1998), Gosliner et al. (2008). Distribution: Indo-West Pacific (from East Africa to Australia and Japan) (Tibirica et al. 2017). 187. Pleurobranchaea maculata (Quoy & Gaimard, 1832) Previous HK record: Tsi and Ma (1982), Jensen (1998). Distribution: Indo-West Pacific (from Sri Lanka to Japan, Australia and New Zealand), introduced to western Atlantic (Argentina) (Willan 1983; Jensen 1998). Family Pleurobranchidae Gray, 1827 188. Berthellina citrina (Rüppell & Leuckart, 1828)* (Fig. 8P) Previous HK record: Morton and Morton (1983) (as Berthellina delicata), Jensen (1998). Distribution: Indo-Pacific (from East Africa to Japan, Australia, New Zealand and Fiji) (Coleman 2008). 189. Pleurobranchus forskalii Rüppell & Leuckart, 1828* (Fig. 8Q) Previous HK record: None. Distribution: Indo-Pacific (from East Africa to Japan, Solomon Islands, Australia, New Caledonia and Fiji) (Mehrotra et al. 2021). 190. Pleurobranchus peronii Cuvier, 1804* (Fig. 8R) Previous HK record: None. Distribution: Indo-Pacific (from South Africa to South Korea, Australia, New Caledonia, Cook Islands and Hawaii) (Coleman 2008; Tibirica et al. 2017). Superorder Ringiculimorpha Superfamily Ringiculoidea Philippi, 1853 Family Ringiculidae Philippi, 1853 191. Ringicula doliaris Gould, 1860 Previous HK record: Lin (1990b), Jensen (1998). Distribution: western Pacific (China, Indonesia, Australia, Japan) (Jensen 1998; Beechey 2012). Subterclass Tectipleura Superorder Acochlidiimorpha Superfamily Acochlidioidea Küthe, 1935 Family Pseudunelidae Rankin, 1979 192. Pseudunela cornuta (Challis, 1970) Previous HK record: Hughes (1991), Jensen (1998). Distribution: western Pacific (Hong Kong, Solomon Islands) (Jensen 1998). Order Aplysiida Superfamily Aplysioidea Lamarck, 1809 Family Aplysiidae Lamarck, 1809 193. Aplysia argus Rüppell & Leuckart, 1830* (Fig. 9A) Previous HK record: Tsi and Ma (1982) (as Aplysia dactylomela), Lin (1990b) (as Aplysia dactylomela), Jensen (1998) (as Aplysia dactylomela). Distribution: Indo-Pacific (from East Africa to Hawaii and Samoa) (Jensen 1998). 194. Aplysia concava Bergh, 1905* (Fig. 9B) Previous HK record: None. Distribution: western Pacific (Hong Kong, Australia) (Burn 2006). 195. Aplysia japonica Sowerby, 1869* (Fig. 9C) Previous HK record: None. Distribution: western Pacific (Hong Kong, Japan, South Korea) (Golestani et al. 2019). 196. Aplysia kurodai Baba, 1937* (Fig. 9D) Previous HK record: Tsi and Ma (1982), Lin (1990b), Jensen (1998). Distribution: western Pacific (Hong Kong, Taiwan, Japan, South Korea) (Coleman 2008; Mehrotra et al. 2021). 197. Aplysia nigrocincta von Martens, 1880* (Fig. 9E) Previous HK record: None. Distribution: Indo-West Pacific (from East Africa to Hong Kong, the Philippines, Indonesia, Papua New Guinea and Vanuatu) (Mehrotra et al. 2021). 198. Aplysia oculifera Adams & Reeve, 1850* (Fig. 9F) Previous HK record: None. Distribution: Indo-West Pacific (from East Africa to Japan, South Korea and Australia) (Coleman 2008). 199. Aplysia sp.* (Fig. 9G) Previous HK record: None. 200. Bursatella leachii Blainville, 1817* (Fig. 9H) Previous HK record: Tsi and Ma (1982), Morton and Morton (1983), Lin (1990b), Jensen (1998). Distribution: circum-tropical/temperate (Coleman 2008). 201. Dolabrifera dolabrifera (Rang, 1828)* (Fig. 9I) Previous HK record: Lin (1990b). Distribution: circum-tropical/temperate (Coleman 2008). Order Cephalaspidea Superfamily Bulloidea Gray, 1827 Family Bullidae Gray, 1827 202. Bulla ampulla Linnaeus, 1758 Previous HK record: Tsi and Ma (1982), Morton page 23 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan and Morton (1983), Lin (1990b), Jensen (1998). Distribution: Indo-Pacific (from East Africa to Japan, Guam, Australia, Fiji and Line Islands) (Malaquias and Reid 2009). Superfamily Cylichnoidea H. Adams & A. Adams, 1854 Family Cylichnidae H. Adams & A. Adams, 1854 203. Semiretusa borneensis (Adams, 1850) Previous HK record: Lin (1990b) (as Retusa boenensis), Jensen (1998). Distribution: western Pacific (China) (Jensen 1998). Superfamily Haminoeoidea Pilsbry, 1895 Family Haminoeidae Pilsbry, 1895 204. Haloa japonica (Pilsbry, 1895)* (Fig. 9J) Previous HK record: Morton and Morton (1983), Jensen (1998). Distribution: western Pacific (Hong Kong, Taiwan, Japan), introduced to eastern Pacific (Canada, USA), eastern Atlantic (Spain, France) and eastern Mediterranean (Italy, Greece) (Gosliner and Behrens 2006). 205. Haminoea yamagutii (Habe, 1952) Previous HK record: Jensen (1998). Distribution: western Pacifc (Hong Kong, Japan) (Jensen 1998). Superfamily Philinoidea Gray, 1850 (1815) Family Aglajidae Pilsbry, 1895 (1847) 206. Chelidonura amoena Bergh, 1905* (Fig. 9K) Previous HK record: None. Distribution: Indo-West Pacific (from Christmas Island and Malaysia to Japan and Australia) (Coleman 2008). 207. Chelidonura hirundinina (Quoy & Gaimard, 1833)* (Fig. 9L) Previous HK record: None. Distribution: Indo-Pacific (from East Africa to Japan, Solomon Islands, Austalia, Fiji and Hawaii) and western Atlantic (Florida, the Caribbean) (Coleman 2008). 208. Niparaya regiscorona (Bertsch, 1972)* (Fig. 9M) Previous HK record: None. Distribution: Indo-Pacific (eastward to Mexico) (Gosliner et al. 2018). 209. Niparaya sp.* (Fig. 9N) Previous HK record: None. 210. Philinopsis falciphallus Gosliner, 2011* (Fig. 9O) Previous HK record: None. Distribution: Indo-West Pacific (Hong Kong, the Red Sea, the Philippines, Indonesia, Marshall Islands, Australia) (Gosliner 2011). 211. Philinopsis speciosa Pease, 1860* (Fig. 9P) Previous HK record: Jensen (1998). Distribution: Indo-Pacific (from East Africa to Australia, Fiji, Japan, South Korea and Hawaii) (Mehrotra et al. 2021). 212. Tubulophilinopsis lineolata (H. Adams & A. Adams, 1854)* (Fig. 9Q) Previous HK record: None. Distribution: Indo-West Pacific (Hong Kong, Thailand, the Philippines, Australia) (Coleman 2008). 213. Tubulophilinopsis pilsbryi (Eliot, 1900)* (Fig. 9R) Previous HK record: None. Distribution: Indo-Pacific (from East Africa to Palau, Australia, Vanuatu, Fiji, Marshall Islands and Hawaii) (Mehrotra et al. 2021). Family Gastropteridae Swainson, 1840 214. Gastropteron minutum Ong & Gosliner, 2017* (Fig. 10A) Previous HK record: None. Distribution: western and central Pacific (Hong Kong, the Philippines, Japan, Marshall Islands, Hawaii) (Ong et al. 2017; Gosliner et al. 2018). 215. Siphopteron makisig Ong & Gosliner, 2017* (Fig. 10B) Previous HK record: None. Distribution: western Pacific (Hong Kong, the Philippines, Indonesia, Australia) (Mehrotra et al. 2021). Family Philinidae Gray, 1850 (1815) Subfamily Philininae Gray, 1850 (1815) 216. Philine paucipapillata Price, Gosliner & Valdés, 2011* (Fig. 10C) Previous HK record: Lin (1990b) (as Philine orientalis), Morton and Chiu (1990) (as Philine orientalis), Morton and Morton (1983) (as Philine orientalis), Jensen (1998) (as Philine orientalis), Price et al. (2011). Distribution: western Pacific (Hong Kong, Cambodia) (Price et al. 2011). 217. Philine vitrea Gould, 1859 (taxon inquirendum) Previous HK record: Lin (1990b), Jensen (1998). Distribution: western Pacific (China, Japan) (Jensen 1998). 218. Yokoyamaia orientalis Lin, 1990 Previous HK record: Lin (1990a). Distribution: Hong Kong (Lin 1990a). page 24 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan Fig. 9. (A) Aplysia argus; (B) Aplysia concava; (C) Aplysia japonica; (D) Aplysia kurodai; (E) Aplysia nigrocincta; (F) Aplysia oculifera; (G) Aplysia sp.; (H) Bursatella leachii; (I) Dolabrifera dolabrifera; (J) Haloa japonica; (K) Chelidonura amoena; (L) Chelidonura hirundinina; (M) Niparaya regiscorona; (N) Niparaya sp.; (O) Philinopsis falciphallus; (P) Philinopsis speciosa; (Q) Tubulophilinopsis lineolata; (R) Tubulophilinopsis pilsbry. Photographs by Tim Lam (A–D, G, K, M, O, P), Sze Yiu Ng (E), Gomen See (F, H, I), AFCD (J), Bell Kwok (L), Alice Au (N), Grape Tang (Q) and Peggie Hon (R). page 25 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan phylogeny and diversity of the bat-winged slugs (Heterobranchia: Gastropteridae). Zool J Linn 180:755–789. doi:10.1093/ zoolinnean/zlw018. Orr J. 1980. Annotated checklist of Hong Kong nudibranchs. In: Morton, B. (Ed.), The Malacofauna of Hong Kong and Southern China. Hong Kong University Press, Hong Kong, pp. 109–117. Orr J. 1981. Hong Kong Nudibranchs. Urban Council, Hong Kong. Picton B. 2001. Eubranchus misakiensis from Hong Kong. Sea Slug Forum. Australian Museum, Sydney. Available at: http://www. seaslugforum.net/find/3936. Picton B. 2002. Notobryon from Hong Kong. Sea Slug Forum. Australian Museum, Sydney. Available at: http://www. seaslugforum.net/find/5948. Accessed 1 Nov. 2021. Pola M, Camacho-Garcia YE, Gosliner TM. 2012. Molecular data illuminate cryptic nudibranch species: the evolution of the Scyllaeidae (Nudibranchia: Dendronotina) with a revision of Notobryon. Zool J Linn 165:311–336. doi:10.1111/j.10963642.2012.00816.x. Price RM, Gosliner TM, Valdés Á. 2011. Systematics and phylogeny of Philine (Gastropoda: Opisthobranchia), with emphasis on the Philine aperta species complex. Veliger 51:1–58. Rudman WB. 1978. The dorid opisthobranch genera Halgerda Bergh and Sclerodoris Eliot from the Indo-West Pacific. Zool J Linn 62:59–88. doi:10.1111/j.1096-3642.1978.tb00523.x. Rudman WB. 1982. The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris quadricolor, C. lineolata and Hypselodoris nigrolineata colour groups. Zool J Linn Soc 76:183–241. doi:10.1111/j.1096-3642.1982.tb02182.x. Rudman WB. 1983. The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris splendida, C. aspersa and Hypselodoris placida colour groups. Zool J Linn Soc 78:105–173. doi:10.1111/j.1096-3642.1983.tb00864.x. Rudman WB. 1985. The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris aureomarginata, C. verrieri and C. fidelis colour groups. Zool J Linn Soc 83:241–299. doi:10.1111/j.1096-3642.1985.tb00875.x. Rudman WB. 1986a. The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: the genus Glossodoris Ehrenberg (= Casella, H. & A. Adams). Zool J Linn Soc 86:101– 184. doi:10.1111/j.1096-3642.1986.tb01810.x. Rudman WB. 1986b. The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Noumea purpurea and Chromodoris decora colour groups. Zool J Linn 86:309–353. doi:10.1111/j.1096-3642.1986.tb01814.x. Rudman WB. 1987a. The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chrornodods epicuria, C. aureopurpurea, C. anndata, C. coi and Risbecia tryoni colour groups. Zool J Linn Soc 90:305–407. doi:10.1111/j.10963642.1987.tb01357.x. Rudman WB. 1987b. The genus Trapania (Nudibranchia: Goniodorididae) in the Indo-West Pacific. J Molluscan Stud 53:189–212. doi:10.1093/mollus/53.2.189. Rudman WB. 1988. The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: the genus Ceratosoma J. E. Gray. Zool J Linn 93:133–185. doi:10.1111/j.1096-3642.1988. tb01531.x. Rudman WB. 1990. The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: further species of Glossodoris, Thorunna and the Chromodoris aureomarginata colour group. Zool J Linn Soc 100:263–326. doi:10.1111/j.10963642.1990.tb01864.x. Rudman WB. 1991. Further studies on the taxonomy and biology of the octocoral-feeding genus Phyllodesmium Ehrenberg, 1831 (Nudibranchia: Aeolidoidea). J Molluscan Stud 57:167–203. doi:10.1093/mollus/57.2.167. Rudman WB. 2001a. Cerberilla sp. 4. Sea Slug Forum. Australian Museum, Sydney. Available at: http://www.seaslugforum.net/ factsheet/cerbsp4. Accessed 1 Nov. 2021. Rudman WB. 2001b. Phidiana anulifera (Baba, 1949). Sea Slug Forum. Australian Museum, Sydney. Available at: http://www. seaslugforum.net/factsheet/phidanul. Accessed 1 Nov. 2021. Rudman WB. 2004. Further species of the opisthobranch genus Okenia (Nudibranchia: Goniodorididae) from the Indo-West Pacific. Zootaxa 695:1–70. doi:10.11646/zootaxa.695.1.1. Rudman WB. 2005. Elysia hirasei Baba, 1955. Sea Slug Forum. Australian Museum, Sydney. Available at: http://www. seaslugforum.net/factsheet/elyshira. Accessed 1 Nov. 2021. Rudman WB. 2007. Comment on Dendrodoris from Hong Kong by Felix Poon. Sea Slug Forum. Australian Museum, Sydney. Available at: http://www.seaslugforum.net/find/20653. Accessed 1 Nov. 2021. Rudman WB, Avern GJ. 1989. The genus Rostanga Bergh, 1879 (Nudibranchia: Dorididae) in the Indo-West Pacific. Zool J Linn Soc 96:281–338. doi:10.1111/j.1096-3642.1989.tb02261.x. Rudman WB, Darvell BW. 1990. Opisthobranch molluscs of Hong Kong: Part 1. Goniodorididae, Onchidorididae, Triophidae, Gymnodorididae, Chromodorididae (Nudibranchia). Asian Mar Biol 7:31–79. Rudman WB, Darvell BW. 2001. Phyllidia ocellata from Hong Kong. Sea Slug Forum. Australian Museum, Sydney. Available at: http://www.seaslugforum.net/find/5204. Accessed 1 Nov. 2021. Sanchez-Escalona KP. 2019. Elysia leucolegnote (Opistobranchia: Sacoglossa) Jensen 1990, a new record for the Verde Island Passage, Philippines. The Palawan Scientist 11:42–48. Smith SDA, Davis TR. 2019. Slugging it out for science: volunteers provide valuable data on the diversity and distribution of heterobranch sea slugs. Molluscan Res 39:214–223. doi:10.1080 /13235818.2019.1594600. Solanki D, Kanejiya J, Gohil B. 2017. Studies on ecological status, nutritive values and exploitation of Peronia verruculata, Cuvier, 1830 (Gastropoda: Onchidiidae) from Gulf of Khambhat, India. J Zool Stud 4:24–28. Swennen C. 2007. Costasiella coronata, new species, and a revised diagnosis for the family Costasiellidae (Mollusca: Opisthobranchia: Sacoglossa). Raffles Bull Zool 55:355–362. Tibirica Y, Pola M, Cervera JL. 2017. Astonishing diversity revealed: an annotated and illustrated inventory of Nudipleura (Gastropoda: Heterobranchia) from Mozambique. Zootaxa 4359:1–133. doi:10.11646/zootaxa.4359.1.1. Trowbridge CD, Hirano YJ, Hirano YM. 2008. Sacoglossan opisthobranchs associated with the green macroalgae Codium spp. on Pacific rocky shores of Japan. Venus 66:175–190. Tsi CY, Ma ST. 1982. A preliminary checklist of the marine Gastropoda and Bivalvia (Mollusca) of Hong Kong and Southern China. In: Morton, B., Tseng, C.K. (Eds.), The Marine Flora and Fauna of Hong Kong and Southern China. Hong Kong University Press, Hong Kong, pp. 431–458. Vadher P, Kardani H, Beleem I. 2020. An annotated checklist of sea slug fauna of Gujarat coast, India. J Threat Taxa 12:15835– 15851. doi:10.11609/jott.5278.12.8.15835-15851. Valdes A. 2002. Review of the genus Actinocyclus Ehrenberg, 1831 (Ophisthobranchia: Doridoidea). Veliger 45:193–202. Willan RC. 1983. New Zealand side-gilled sea slugs (Opisthobranchia: Notaspidea: Pleurobranchidae). Malacologia 23:254. Wong KT, Ng TY, Tsang RHL, Ang P Jr. 2017. First observation of the nudibranch Tenellia feeding on the scleractinian coral Pavona decussata. Coral Reefs 36:1121. doi:10.1007/s00338-017-16038. Yonow N. 2012. Opisthobranchs from the western Indian Ocean, with descriptions of two new species and ten new records page 32 of 33Zoological Studies 61:52 (2022) © 2022 Academia Sinica, Taiwan (Mollusca, Gastropoda). ZooKeys 197:1–129. doi:10.3897/ zookeys.197.1728. Yonow N. 2015. Sea Slugs: unexpected biodiversity and distribution. In: The Red Sea. Springer, Berlin, Heidelberg, pp. 531–550. Yonow N. 2018. Red Sea Opisthobranchia 5: new species and new records of chromodorids from the Red Sea (Heterobranchia, Nudibranchia, Chromodorididae). ZooKeys 770:9–42. doi:10.3897/zookeys.770.26378. Zhang K, Wang D, Shen H, Qian J, Guan J, Wu H, Gao Y. 2017. Redescription of Platevindex mortoni (Gastropoda: Eupulmonata: Onchidiidae) from China. Molluscan Res 37:72– 78. doi:10.1080/13235818.2016.1223535. page 33 of 33Zoological Studies 61:52 (2022)