Elysia timida, the Green Elysia, is a species of sacoglossan sea slug, a marine opisthobranch gastropod mollusk endemic to the Mediterranean Sea, although it is also found in the eastern Atlantic Ocean and in the Caribbean Sea. It is also known by another two synonyms, Elysia viridis and Notarchus timidus.
The genus Elysia belongs to the family Plakobranchidae, superfamily Plakobranchoidea, order Sacoglossa, class Gastropoda, phylum Mollusca and kingdom Animalia.
The maximum length of Elysia timida is 10 mm, the width 1.3 to 1.4 mm. The parapodia are low, with a few higher projections which give this slug a hunch-backed outline when seen from the side. On the first projection of the left parapodium there is a tiny protuberance which fits into a small groove in the first projection of the right parapodium.
The colour of Elysia timida is chalk white with a few vermilion (brilliant red) dots. The brightly green branches of the liver shine through the sides of the body, the inner side of the parapodia and the back between the parapodia behind the cardiac region. The foot is divided by a transverse furrow while the rhinophores are rather thick and rolled up as usual.
Elysia timida lives mostly epifaunally on algae and rocks in shallow, sun-lit water. It is found on and eating Acetabularia acetabulum in warm months and Padina pavonia in cooler months. This species can only eat young pre-calcified stalks of A. acetabulum, from which it retains functional symbiotic chloroplasts from its food within the cells of its digestive system, that are able to continue photosynthesis in the slug’s tissues. It has a short planktonic lecithotrophic (non-feeding) larval phase when its algae food source is depleted and a “direct”, non-planktonic developmental mode with intracapsular metamorphosis when its food is plentiful.
Elysia timida also produces a defensive secretion that deters predatory fish that attempt to eat it, such as Thalassoma pavo, the ornate wrasse.
The photo of this Green Elysia was taken at a depth of 4m at Reqqa Point, on Gozo’s north coast.
Photos taken by Brian Azzopardi