On the Plakobranchidae (Gastropoda, Sacoglossa) from soft sediment habitats of Koh Tao, Gulf of Thailand, with descriptions of two new species Author Mehrotra, Rahul Reef Biology Research Group, Department of Marine Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand & Conservation Diver, 7321 Timber Trail Road, Evergreen, Colorado, 80439, USA Author Gutierrez, Manuel Caballer The 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 Scott, Chad M. 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 Conservation Diver, 7321 Timber Trail Road, Evergreen, Colorado, 80439, USA & Research Center on Animal Cognition (CRCA), Center for Integrative Biology (CBI); CNRS, University Paul Sabatier - Toulouse III, France Author Chavanich, Suchana 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 https://orcid.org/0000-0001-6266-7300 suchana.c@chula.ac.th text ZooKeys 2020 969 85 121 http://dx.doi.org/10.3897/zookeys.969.52941 journal article http://dx.doi.org/10.3897/zookeys.969.52941 1313-2970-969-85 6D442A10F3514B9C836441B47A0B145A 75A12CC829765BCCA32A15CE409DCC18 Genus Elysia Risso, 1818 Diagnosis. Body smooth to papillate, with parapodia that may cover much of the dorsal surface; however, parapodia can be highly variable and may not be held close to the body. Head differentiated from the body with eyes behind dorsal rhinophores. Dorsal sinuses usually branched, anus anterodorsal, reproductive system pseudo-diaulic or triaulic, penis normally unarmed although a hollow apical stylet may be present. Radular teeth blade-shaped ranging from denticulate to smooth.