An updated inventory of sea slugs from Koh Tao, Thailand, with notes on their ecology and a dramatic biodiversity increase for Thai waters Author Mehrotra, Rahul Reef Biology Research Group. Department of Marine Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand & Aow Thai Marine Ecology Center, Koh Mun Nai, Kram, Klaeng District, Rayong 21110, Thailand Author A. Caballer Gutierrez, Manuel American University of Paris, Department of Computer Science Math and Environmental Science, 6 rue du Colonel Combes, 75007 Paris, France & Museum national d'Histoire naturelle, 55 rue de Buffon, 75005 Paris, France Author M. Scott, Chad Conservation Diver. 7321 Timber Trail Road, Evergreen, Colorado, 80439, USA Author Arnold, Spencer Conservation Diver. 7321 Timber Trail Road, Evergreen, Colorado, 80439, USA Author Monchanin, Coline Aow Thai Marine Ecology Center, Koh Mun Nai, Kram, Klaeng District, Rayong 21110, Thailand & Research Center on Animal Cognition (CRCA), Center for Integrative Biology (CBI); CNRS, University Paul Sabatier, Toulouse III, France Author Viyakarn, Voranop https://orcid.org/0000-0002-2089-6356 Reef Biology Research Group. Department of Marine Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand Author Chavanich, Suchana https://orcid.org/0000-0001-6266-7300 Reef Biology Research Group. Department of Marine Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand & Center of Excellence for Marine Biotechnology, Department of Marine Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand suchana.c@chula.ac.th text ZooKeys 2021 2021-06-09 1042 73 188 http://dx.doi.org/10.3897/zookeys.1042.64474 journal article http://dx.doi.org/10.3897/zookeys.1042.64474 1313-2970-1042-73 9CF986D86A474E179A67245C78FB8AFD 1BB0A10A35DD5541850FDAFFDB7119C2 Hypselodoris cf. maritima (Baba, 1949) Figure 11E, F Material examined. Three specimens 14-30 mm , TT; two specimens 15-25 mm , SWP; one specimen 20 mm , SR. Ecology. On rocks and rubble within coral reef. Depth 5-25 m. Distribution. Hypselodoris maritima is recorded from Japan ( Baba 1949 ), Vietnam ( Martynov and Korshunova 2012 ), Taiwan ( Su et al. 2009 ), the Philippines, Indonesia, Hong Kong, Papua New Guinea, and Australia ( Gosliner et al. 2008 ). The species is also recorded as being present in Thailand by Gosliner et al. (2008) but no confirmed records of this or similar species outside of Koh Tao have been found in the literature. Remarks. Initially recorded as H. maritima from Koh Tao ( Mehrotra and Scott 2016 ), further observations have shown variation in external morphology that diverges from the original description. In general, the dorsal surface is always white with scattered and slightly raised spots. While many individuals bear the deep blue to black 'longitudinal streaks' along the central dorsal surface, in others these are broken lines or even entirely disconnected spots of varying sizes. Rhinophore clubs range from entirely orange to white with orange apices, stalks always translucent white. The blue marginal band is always separated from the yellow submarginal band by the same white as the dorsum, and both bands are often broken or rows of pigmented spots, matching variation in the dark pigmentation. There are always deep blue-black spots between marginal and submarginal bands/rows, that may vary in size and often extend to the mantle edge. While closer examination may reveal individuals from Koh Tao and the nearby pinnacles to be more than one species, the population is here treated as a single variable species.