Chromodoris geminus? from South Africa

November 11, 1999
From: Valda Fraser

Dear Bill
This nudibranch occurs quite commonly in our area.  When it is small its body profile is very flat.  However, as it grows the body becomes much more raised.  Smaller specimens are less bright in colour.  The colour of the animal becomes increasingly rich with age.  I am sending you an image of a half grown one,  The big ones are troublesome to me, as they do not fit into my 70mm framer.

Locality:    South Coast KwaZulu/Natal - SOUTH AFRICA, Near Port Shepstone
Rocky Reef, 20 - 25m, October 1999
Size: 40mm

Valda Fraser

Fraser, V., 1999 (Nov 11) Chromodoris geminus? from South Africa. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Valda,
This looks quite like Chromodoris geminus which I described from Tanzania in 1987. Terry Gosliner has also reported C. geminus from South Africa (Chromodoris sp. 3. in his book), but I am not at all sure that your animal is the same.

It's a little bit deeper in colour than the C. geminus and differs in having the purple right at the mantle edge rather than submarginally. There is also a distinct deep yellow submarginal band in C. geminus while in your South African animals the yellow-brown background colour on the mantle is uniform. Also in C. geminus there are spots on the foot and a white edge, while in your animal I can't see if there are any spots on the foot but it has a purple edge. The rhinophore clubs in your animal are purple not yellowish. All in all I think this may be a mimic of C. geminus.

A very distinctive behavioural chracteristic of C. geminus which you can see in the photo at the top of the page is that the mantle edge is raised and lowered in one movement all around the mantle edge. Does your animal do that? C. kuniei from the western Pacific also flaps its mantle like this.

Your photos are very useful. The more photos we can get of species throughout their geographic range, the more chance we have of understanding the limits of a species' geographic distribution and colour variation. If you have photos which show the foot and mantle edge more clearly they could be useful.

Best wishes,
Bill Rudman.

Rudman, W.B., 1999 (Nov 11). Comment on Chromodoris geminus? from South Africa by Valda Fraser. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Related messages

  1. Chromodoris cf. geminus from Mauritius
    From: Marina Poddubetskaia, November 21, 2002
  2. Re: Movement in Chromodoris cf.geminus
    From: Lindsay Warren, June 3, 2002
  3. Movement in Chromodoris cf. geminus
    From: Valda Fraser, December 2, 1999
  4. Re: Chromodoris geminus? from Sth Africa
    From: Valda Fraser, November 14, 1999

Show factsheet and all related messages