Cyerce nigra and C. nigricans – swimming behaviour

December 5, 2001
From: Julie Marshall

Dear Bill,

On a recent trip to Heron Island I found a Cyerce nigra moving across the sand flats at low tide. It was 18 mm in size. Although Cyerce nigricans is comparatively common at Heron Island this was the first time I have found this species with the transverse stripes on the outside of the cerata rather than the spots on both sides of the cerata of Cyerce nigricans.

When disturbed it swam very vigorously, much the same as I have observed with Cyerce sp. 1. I have not, however, ever seen Cyerce nigricans swim in this manner although I have picked it up and irritated it and have only observed it moving its cerata backwards and forwards - not vigorously swimming through the water. Is it possible that the swimming behaviour attributed to Cyerce nigricans is perhaps a confusion with the behaviour of C. nigra which some people think is a colour form of C. nigricans? I would be interested to hear of observations, or pictures of C. nigricans swimming. This could possibly be another distinguishing feature between the two species (as well as the pattern differences and the observations by Clay Carlson and Patty-Jo Hoff that C. nigra feeds on Udotea rather than Chlorodesmis). Note that although one picture shows some Chlorodesmis in the background I placed the animal on this alga – it was not feeding on it!

Best wishes
Julie Marshall

Marshall, J., 2001 (Dec 5) Cyerce nigra and C. nigricans – swimming behaviour. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Julie,
It would certainly be interesting to hear of any other swimming observations of the two species.
Best wishes,
Bill Rudman


Cyerce nigra

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