Leslie Chan's Elysia from Hong Kong

July 19, 2001
From: Kathe Jensen

Dear Bill,
I am pretty sure Leslie Chan's Elysia is what I have been calling Elysia japonica Eliot, 1913. It is difficult to see the tip of the tail, but I think it is also black/ dark (like tips of rhinophores). The species varies in colouration depending on the food alga - I have seen pinkish specimens, but unfortunately the diver who collected these specimens did not collect any algae, so I don't know if it actually eats red algae. The yellow dots may be more conspicuous, and there may be orange and iridescent blue dots as well. Also it may have more dark brown pigment on the parapodia. Usually it feeds on Cladophora and similar green algae.

A similar looking species, Elysia flavomacula Jensen, 1990, has one large yellow spot on the neck, and is generally much paler than this one. The rhinophores appear thicker and not narrowing towards the tips, and it does not have a black tip of the tail. Also, radular teeth are completely different, being blade-shaped in E. flavomacula and with rounded tips and lateral flanges in E. japonica.

I hope this will be sufficient information. At the time I described the Hong Kong specimens, I thought they looked very similar to the species Brian Brandley worked on and identified as E. furvacauda. After examining the type specimen of this species in the Museum of Victoria, I am not
so sure about that (or maybe Brian Brandley was not using E. furvacauda?).

• Jensen,KR (1985): Annotated checklist of Hong Kong Ascoglossa (Mollusca: Opisthobranchia), with descriptions of four new species. In: Proceedings of the 2nd International Workshop on the Malacofauna of Hong Kong and Southern China, Hong Kong, 1983. (Eds: Morton,B; Dudgeon,D) Hong Kong University Press, Hong Kong, 77-107.
• Jensen,KR (1990): Three new species of Ascoglossa (Mollusca, Opisthobranchia) from Hong Kong, and a description of the internal anatomy of Costasiella pallida Jensen, 1985. In: Proceedings of the 2nd International Marine Biological Workshop: The marine Flora and Fauna of Hong Kong and Southern China, Hong Kong, 1986. (Ed: Morton,B) Hong Kong University Press, Hong Kong, 419-432.

Greetings,
Kathe

jensen@ait.ac.th

Jensen, K., 2001 (Jul 19) Leslie Chan's Elysia from Hong Kong. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/4796

Thanks Kathe,
One value of the Forum is that by building up a collection of colour photos of these species it must surely help to sort out some of the names of the similarly coloured species. I note in your 1985 Hong Kong paper that you suggest that both E. amakusana and E. abei are both probably synonyms of E. japonica. If the identifications on the Forum, based on Japanese usage, are correct then it seems that they are probably distinct species.

I am a little bit concerned with your suggestion that it is possible to identify Eliot's Elysia japonica. The colour description was made from apparently preserved animals
"In all the specimens the rhinophores and tip of tail are conspicuously black or very dark brown. Otherwise the colour is uniform and the best preserved specimen is yellowish brown ....".
If as you say, the radular description is not likely to be accurate, then we have no information in Eliot's description on which to base an identification other than that it was from Japan. I feel it would be better to discard Eliot's name as unidentifiable and use a later name if there is one.

Concerning the species Brian Brandley worked with. There is no problem with identifying it. the problem is whether it has a name. While he was working on this species, he asked me for help in identifying it. It had previously been tentatively identified as E. furvacauda in New South Wales, but I felt it had significant differences to the original description by Burn. Unfortunately no material was available of 'typical' E. furvacauda for comparison. For this reason I suggested Brian identify his animal as Elysia cf. furvacauda and deposit voucher specimens in the Australian Museum collections. I photographed these specimens alive - see top of Elysia cf. furvacauda page - so that they would be identifiable to later workers. Throughout the paper they are referred to as Elysia cf. furvacauda and the identification problem discussed.
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Jul 19). Comment on Leslie Chan's Elysia from Hong Kong by Kathe Jensen. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/4796

Factsheet

Elysia cf. japonica

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