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 * Dermatobranchus sp. 1 Figure 19G, H Material examined. Three specimens 28-40 mm , SB. Ecology. Exclusive to the soft sediment habitats outside the coral reef where it feeds on colonies of the octocoral Dendronephthya sp. Depth 14-24 m. Distribution. Unknown. Remarks. A species that vaguely resembles but is distinct from Dermatobranchus semilunus is regularly recorded from the same habitats and locations as other soft-sediment dwelling members of the genus. Specimens of Dermatobranchus sp. 1 externally appear to have characteristics of D. fasciatus and D. semilunus . All specimens have prominent longitudinal ridges on a generally white dorsum, with numerous black spots of varying sizes distributed along the ridges and margin of the oral veil. The oral veil always has patches of grey and the margin is sometimes pigmented with a yellow-pink band which is often pale or completely absent in some specimens. The dorsal surface usually has a single horizontal diffuse band approximately one third of the total animal length. The foot is pale pink to white, sometimes with numerous small black spots. The rhinophores have white tips, dark clubs with white lines along the lamellae, and white stalks with dark grey pigment along the inner edge of the stalks often forming a dark grey band in between and anterior to the rhinophores.