Black Chelidonura from Lizard island

January 25, 2003
From: Nils Anthes

Hi Bill,
Following on from my earlier message, here is some more information on Chelidonura sandrana and the black 'species' which we have found in separate populations, at Lizard Island.

Yesterday [20 January 2003] we randomly collected 37 animals at a site were only the black Chelidonura " occurs. Today we made some detailed comparisons with C. sandrana and we assume that we are looking at a different species. I attach a picture (made with a strong flash; overexposed because of the black background) . I will list some reasons why we believe this is a distinct species:

• On average, it is strikingly larger than C. sandrana. We will measure the size of the 37 animals during the next days, and can compare it to a sample of > 100 C. sandrana.
• Almost consistently, it has a much longer, slender, elongated tail, reaching up to body length. In C. sandrana , the tail reaches at max half body length, and is generally stumpy and broad.
• It consistently lacks any kind of colour pattern. The whole body is uniformly black (appearing lighter on the picture), with a typical blueish shimmer (that many aglajids have). The head has a broad white margin, that does not narrow at the center. In contrast, all C. sandrana that more or less lack any pattern, are dark brownish and not black, and almost always have at least a few spots somewhere. Besides, the white color at the head is basically absent in the center when viewed dorsally.
• There are a few striking structrual differences. The body usually widens towards the middle, whereas in C. sandrana the body is broadest towards the rear end. Hence, it appears to be much more elegant. The headshield extends further towards the rear than in C. sandrana.

We are very curious to hear what you think ...
Kind regards

Anthes N., 2003 (Jan 25) Black Chelidonura from Lizard island. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Nils,
I fully agree that this is different from C. sandrana. It obviously has similar habits, and from other reports on the Forum, it probably has a similar distribution. It is at present on the Forum as Chelidonura sp. 1 .

What I find particularly interesting is your discovery that the two species live segregated from one another. It would be interesting to know if this is the result of slight differences in physical requirements, in food, or perhaps chance settlement of larval swarms. I can't believe its because they don't like each other, but as behaviourists, I guess it would be an interesting thing for you to investigate.

Thanks for sharing all your interesting finds,
Best wishes,
Bill Rudman

Rudman, W.B., 2003 (Jan 25). Comment on Black Chelidonura from Lizard island by Nils Anthes. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Chelidonura sp. 1.

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