Nembrotha milleri with orange spots?

May 10, 2006
From: Wilhelm van Zyl

Hi Bill,

I came across these 2 animals, one green with black spots and one dark red with bright red spots. I am pretty sure the green animal is Nembrotha milleri, but the red one is giving me problems. I had 2 theories at the time, They are either mating or the green one is eating the red one. The upper photo was taken by my dive buddy Anelda at Nugwi on Unguja Island. The middle photo I took at Pemba Island. So this was not a chance meeting by two unrelated individuals. The lower photo might also be of Nembrotha milleri, but this one was very dark green, almost purple with red spots. I have also seen a red spotted one on its own but unfortunately could not get a picture.

Locality: Upper: Unguja Island, 16 m. Photo: Anelda Lategan. Middle: Pemba Island, 15 m. Photo: Wilhelm van Zyl. Lower: Pemba Island, 10 m. Photo: Wilhelm van Zyl. Zanzibar, Tanzania. Indian Ocean. Lengths: 8 - 10 cm. 10 October 2005


Van Zyl, F.W., 2006 (May 10) Nembrotha milleri with orange spots?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Wilhelm,
This is a very interesting find. The green animal is what I was calling Nembrotha sp. 14 but have tentatively accepted as the western Indian Ocean form of N. milleri, although Bernard Picton remains unconvinced.

 As you say, your photos are open to a number of interpretations. Clearly, on two separate occasions black-spotted and red-spotted animals were found together. In your upper photo I assume they are both attracted to the green masses in your photo which we know are the ascidian food of the black-spotted N. milleri [aka Nembrotha sp. 14]. In the middle photo I am sure the black-spotted animal is not eating the red spotted one because it feeds exclusively on ascidians. So they could be mating or they could be feeding close together. The lower photo suggests that both the second two alternatives - mating or feeding together - could be correct because it appears to be a nice intermediate form between the black-spotted animals and the red-spotted ones.

I think what you have discovered is another species which varies in colour from black to red (or orange-red) spots. This would be exciting if it were the first time we had seen this happening in a species of Nembrotha, but I think it is even more exciting that this is at least the third species which does this. The most spectacular example is Nembrotha kubaryana, but we also see it happening in Nembrotha guttata, suggesting a common cause for this phenomenon. Yesterday I briefly discussed [message #16537] a specimen of Risbecia tryoni with orange-red spots instead of the usual blackish purple. I would not be at all surprised if all these black - orange [red, brown] colour swaps had a common cause.

So in answer to your question - I don't think one's eating the other but it's possible they are mating. And thanks for showing us that N. milleri - or its East African lookalike - has a red-spotted colour form.

Best wishes,
Bill Rudman

Rudman, W.B., 2006 (May 10). Comment on Nembrotha milleri with orange spots? by Wilhelm van Zyl. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


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