Elysia trilobata
Heller & Thompson, 1983
Order: SACOGLOSSA
Superfamily: ELYSIOIDEA
Family: Elysiidae
DISTRIBUTION
Known only from the Red Sea
PHOTO
Eilat, Tables South, Israel. Red Sea (Gulf of Eilat). Depth: 28 m. Length: ca 1.5 cm. 04 March 2005. sea grass. Photographer: Binyamin and Shulamit Koretz
This species was described from a single 8 mm long specimen from the Red Sea coast of Sudan. The two most characteristic features were the shape of the parapodia, divided into three unequally sized and shaped lobes, and the large rounded tubercles scattered over the parapodia, rhinophores and body.
Each parapodia has the edge extended into three distinct lobes. The most anterior lobe extends the furthest, while the second lobe is lower but much longer, and the third is very small, almost a widening of the posterior tip of the foot. The lobes are thicker and pigmented with an opaque whitish colouration. Between the lobes, the tissue is transparent with the green of the digestive gland showing through. In the right photo above, part of the parapodia between the first and second lobes appears to be absent.
Heller & Thompson's animal was described as having a ground colour of light green with scattered dark green specks, giving an overall light green appearance. The rounded tubercles on the outside of the parapodia were white while those along the edge were white with a yellow centre. Much of the outside of the anterior parapodial lobe was maroon red, and there was a maroon red patch covering much of the head. The rhinophores have patches of maroon and the tips were white.
The animals from Eilat on the Forum are the first record of this species since its original description. These specimens differ in having blue on the rounded tubercles, blue tips to the rhinophores and to the posterior tip of the foot. In these specimens, the maroon red of the Sudanese specimen is replaced by an opaque brownish white. It grows to approx 15 mm in length.
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Heller, J. & Thompson, T. E. (1983) Opisthobranch molluscs of the Sudanese Red Sea. Zoological Journal of the Linnean Society, 78: 317-348.
Rudman, W.B., 2005 (March 12) Elysia trilobata Heller & Thompson, 1983. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/elystril
Related messages
More photos of Elysia trilobata
March 14, 2005
From: Binyamin Koretz
Hi Bill,
Not the best photos, but this was quite small. We encountered what looks like an Elysiid sp. in a grassy area that often fruitful for 'branching.
Do you have any idea what this is?
Locality: Eilat, Tables South, Israel. Red Sea (Gulf of Eilat). Depth: 28 m. Length: approx. 1 cm. 16 February 2005. grassy expanse (with occasional small corals) at foot of slope. Photographer: Binyamin and Shulamit Koretz
Thanks again and regards
Binyamin Koretz
binyamin@koretz.net
Koretz, B., 2005 (Mar 14) More photos of Elysia trilobata. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/13166Dear Binyamin,
As I mention in your accompanying message [#13299], I couldn't identify these as Elysia trilobata from the photos alone because they don't show the typical 'trilobate' shape in this pose. The interesting thing about these photos is that in this contracted pose, the white pigmentation on the lobes is all that can be seen, and may help camouflage the animal in a coral rubble and coral sand locality. In these photo the animal appears to be on a green alga with a distinctive structure like some species of Microdictyon or Boodlea have. Perhaps there is enough structure visible for someone to suggest a possible food plant for this species.
Best wishes,
Bill Rudman
Rediscovery of Elysia trilobata from Red Sea
March 14, 2005
From: Binyamin Koretz
Hi Bill,
Last month, I sent you a couple of poor photos of what looked like a small Elysiid sp. [message #13166], which as yet you haven't posted. We have encountered this slug several more times in the same vicinity, and now we have some halfway decent photos.
Locality: Eilat, Tables South, Israel. Red Sea (Gulf of Eilat). Depth: 28 m. Length: ca 1.5 cm. 04 March 2005. sea grass. Photographer: Binyamin and Shulamit Koretz
Best regards
Binyamin
binyamin@koretz.net
Koretz, B., 2005 (Mar 14) Rediscovery of Elysia trilobata from Red Sea. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/13299
Dear Binyamin,
Sorry I hadn't posted your earlier message but the photos didn't give me any clues to its identity so it was waiting in the 'difficult' basket. However as soon as I saw these photos it reminded me of a species described from Sudan on the basis of one small specimen - Elysia trilobata Heller & Thompson, 1983, and after re-reading their description I am sure that is what your animal is. This is the first record of it since that description in 1983 and so is a very valuable contribution to our knowledge.
I must admit I thought this species must have been based on a damaged, perhaps half-eaten animal, the shape of the [parapodia appearing very strange in Heller & Thompson's drawing. I can see from your photos that their drawing was quite accurate - but the shape is still very strange. In fact in the upper right animal it almost looks as though there is a gap on the right side, between the anterior and middle lobe of the parapodia, making it look as though it has been bitten. I have posted your earlier message as well, as the photos in that message show animals that are not fully extended. In that condition the 'trilobate' shape is not so clear.
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Heller, J. & Thompson, T. E. (1983) Opisthobranch molluscs of the Sudanese Red Sea. Zoological Journal of the Linnean Society, 78: 317-348.
Best wishes,
Bill Rudman
