Elysia pusilla (Bergh, 1871)

Mehrotra, Rahul, A. Caballer Gutierrez, Manuel, M. Scott, Chad, Arnold, Spencer, Monchanin, Coline, Viyakarn, Voranop & Chavanich, Suchana, 2021, An updated inventory of sea slugs from Koh Tao, Thailand, with notes on their ecology and a dramatic biodiversity increase for Thai waters, ZooKeys 1042, pp. 73-188 : 73

* Elysia pusilla (Bergh, 1871) Figure 6A

Material examined.

Three specimens 3-7 mm, CB; one specimen 4 mm, SRB.

Ecology.

Feeds on Halimeda macroloba , on which it is highly cryptic. Host and prey found in soft sediment habitats near coral reefs between 0.5 and 9 m depth. Multiple individuals may be found feeding on a single prey item. Populations of the host algae H. macroloba have been found at only two locations at the island, 6-9 m depth at SRB and a small intertidal patch at site CB at 0.5-1.5 m. The abundance of E. pusilla has been found to be greater at CB than on the larger but less dense population of H. macroloba at site SRB.

Distribution.

Widespread across the Indo-Pacific including the Red Sea ( Yonow 2008), Réunion ( Bourjon et al. 2018), India ( Sreeraj et al. 2012), Singapore ( Jensen 2009), Vietnam ( Martynov and Korshunova 2012), Indonesia ( Eisenbarth et al. 2018), Australia ( Nimbs and Smith 2016), Japan, Guam ( Vendetti et al. 2012), Mexico ( Goddard and Hermosillo 2008), Costa Rica ( García-Méndez and Camacho-García 2016), South Africa, Tanzania, Madagascar, New Caledonia, and Hawaii ( Gosliner et al. 2008). Known from the Andaman waters of Thailand ( Jensen 1992), and here representing a first record for the Gulf of Thailand.

Remarks.

The status of Elysia pusilla and its taxonomic implications for the genus needs closer investigation ( Jensen 2009, 2015; Krug et al. 2016). Recent observations carried out by Mehrotra et al. (2019) indicate that E. pusilla specimens from Koh Tao are considered palatable to opportunistic scleractinian coral predators and are readily consumed by these reef building corals. However, to date, no instances of natural prey capture of E. pusilla by these corals has been documented.

Figures

Figure 6. A Elysia pusilla 7 mm B Elysia cf. tomentosa 37 mm C Thuridilla cf. gracilis 18 mm D Colinatys sp. 3 mm E Aliculastrum cylindricum 30 mm F Aliculastrum debilis 28 mm G A. debilis (shell 12 mm) captured alive and predated by Haptosquilla cf. nefanda H Roxaniella multistriata 9 mm I Atys semistriatus 8 mm J Atys sp. 11 mm K Diniatys dentifer 5 mm L Diniatys dubius 6 mm.