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 * Eubranchus ocellatus (Alder & Hancock, 1864) Figure 20F Material examined. One specimen 22 mm , SN. Ecology. On its prey hydroid Idiellana pristis Lamouroux, 1816 rare in soft sediment habitats and absent from the coral reefs of Koh Tao. Depth 12-24 m. Distribution. Eubranchus ocellatus is known from the Red Sea ( Yonow 2008 ), Australia ( Nimbs and Smith 2016 ), Tanzania, Philippines, Indonesia, and New Caledonia ( Gosliner et al. 2008 ). Here representing a first record for Thai waters and a first record for the genus in the Gulf of Thailand. Remarks. It necessary here to clarify the brief historical records of Eubranchidae in Thai waters. Chavanich et al. (2013) recorded Baeolidia japonica Baba, 1933 from the Gulf of Thailand as a member of the Eubranchidae , which in fact belongs to the Aeolidiidae , as a representation of the first record of the family from Thai waters. Not mentioned in the same review, however, was the observation of Eubranchus rubropunctatus Edmunds, 1969 from the Andaman coast of Thailand ( Neal 2010 ) which is believed to represent the first record of the family from Thai waters.