On the Plakobranchidae (Gastropoda, Sacoglossa) from soft sediment habitats of Koh Tao, Gulf of Thailand, with descriptions of two new species

Abstract

Research in recent years have provided rapid advances in biogeographic and taxonomic documentation of sea slugs around the world. However, efforts are lacking in surveying most coastlines and habitats in South-East Asia. Recent studies from the Gulf of Thailand have indicated that a wealth of unexplored sea slug diversity and ecology may be gained from an investigation of soft sediment habitats beyond the reef slopes. Additionally, the waters of Koh Tao have been found to host regionally high levels of sea slug diversity with several species awaiting taxonomic clarification. In this work the initial findings of an expanded survey effort from the waters around Koh Tao are provided, with the identity of two soft sediment-associated sacoglossan species in the family Plakobranchidae being investigated. By integrating morphological and molecular analyses, the species Plakobranchus noctisstellatussp. nov. and Elysia aowthaisp. nov. are described and species complexes surrounding Plakobranchus ocellatus van Hasselt, 1824 and Elysia japonica Eliot, 1913 are discussed. The topics of morphological variability and the cryptic species problem are also discussed.

An updated inventory of sea slugs from Koh Tao, Thailand, with notes on their ecology and a dramatic biodiversity increase for Thai waters

“…are often abundant in these areas (Mehrotra et al 2019) as well as bryozoans of the family Bugulidae and other known prey items of sea slugs (McDonald and Nybakken 1997), most of which are either rare or entirely absent from hard substrate habitats around Koh Tao. Indeed, such ecological aspects have already been suggested as key drivers in the description of four new species from the soft sediments of Koh Tao (Mehrotra et al 2017(Mehrotra et al , 2020b.…”

“…The internal anatomy of the specimen was not studied and thus it could not be identified to genus level. (Gosliner et al , 2015 and the Gulf of Thailand (Mehrotra et al 2020b).…”

“…Known only from the Philippines, Malaysia, Indonesia, and Papua New Guinea (Meyers-Muñoz et al 2016;Yonow and Jensen 2018). Known from Gulf waters of Thailand (Mehrotra et al 2020b).…”

“…Remarks. Specimens from Koh Tao were recently reviewed (Mehrotra et al 2020b). (Wägele et al 2010), the Philippines, Indonesia, Papua New Guinea, Japan, Guam, and Hawaii Wägele et al 2010).…”

“…Much of this increase was attributed to previously unexplored soft sediment habitats beyond the slope of fringing coral reefs, which appeared to host a high diversity of species that were not seen in shallower habitats nearer to coral reefs. Subsequent surveys in these habitats revealed a number of novel species descriptions and ecological features that had hitherto been overlooked ( Mehrotra et al 2017 , 2019 , 2020b ). In the present work we summarise the findings of dedicated surveys subsequent to these studies and document a further expansion in sea slug biodiversity in Thai waters.…”