Elysia cf. marginata (Pease, 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 cf. marginata (Pease, 1871) Figure 4J

Material examined.

Three specimens 65-82 mm, CB.

Ecology.

Mostly recorded from specimens inhabiting a shallow, isolated patch of Halimeda macroloba Decaisne, 1841 in soft sediment habits, although presumably feeding on other nearby algae. Also observed from shallow coral reef habitats, rarely. Depth 0.5-6 m.

Distribution.

Elysia marginata is at present recorded from the Indo-Pacific including Myanmar ( Sanpanich and Duangdee 2019), Vietnam ( Martynov and Korshunova 2012), Indonesia ( Yonow and Jensen 2018), Australia ( Nimbs and Smith 2016), Japan, Guam, French Polynesia, Vanuatu, and Hawaii ( Krug et al. 2013). Specimens from South Africa, Madagascar, and Réunion ( Gosliner et al. 2008 as Elysia ornata ) also are likely to correspond to this complex. Known from the Andaman waters of Thailand ( Jensen 1992), here representing a first record for the Gulf of Thailand.

Remarks.

Recent molecular investigations ( Krug et al. 2013) have indicated up to four possible clades making up the species Elysia marginata , that was separated from its Caribbean counterpart Elysia ornata (Swainson, 1840), which was formerly considered circumtropical. Yonow and Jensen (2018) further discuss the challenges in assigning all specimens with the ‘characteristic’ orange and black marginal bands on the parapodia to E. marginata as similar species such as E. faustula Bergh, 1871 and E. grandifolia Kelaart, 1858 were described and illustrated with comparable features. Both aforementioned species differ in ground colour or the presence/absence of denticulation on radular teeth, and both of these features have been shown to be variable within a single species and often a single specimen ( Mehrotra et al. 2020b). Therefore, all indications point to a need for a comprehensive analysis integrating morphology, ecology, and molecular data to delineate species in this complex.

Figures

Figure 4. A Costasiella cf. kuroshimae 6 mm B Costasiella usagi 6 mm C Limapontiidae sp. 3 mm D Plakobranchus noctisstellatus 21 mm (photograph by Pau Urgell Plaza) E Plakobranchus ocellatus 32 mm F Plakobranchus papua 27 mm G Plakobranchus papua 21 mm on Holothuria edulis H Elysia aowthai 12 mm I Elysia asbecki 15 mm J Elysia cf. marginata 70 mm K Elysia mercieri 12 mm L Elysia obtusa 9 mm.