What are these two gas flames doing?
Photo submitted by Rene Pretorius
A Risbecia pulchella tailing another one at Sodwana.
This and the next three show two scribbled nudibranchs Doriopsilla miniata meeting and pulling away from each other.
See how the one at the right has pulled its mantle right up to get away from the other one.
Photos Guido Zsilavecz
These two gas flame nudibranchs where caught in a very interesting pose, with the one seemingly pouncing on the other one who seems to be cowering down. What is going on here?
That is hard to say. Nudibranchs have complex behaviour, and different species behave differently. Some "tail" by following another individual by puttings its "nose" on its tail, others flap their mantle as they move, and so on. An interesting read is "Nudibranch Behaviour" by David Behrens which lists a few more.
In my own experience I've seen nudibranchs quickly pull back when touching another individual, so possibly these two inadvertently met and this is their reaction. Another possibility is that, given they are facing right side to right side, is that this may be part of mating behaviour. Nudibranchs have their sexual organs on the right side of the body, and mating thus requires them to meet head to tail, on the right side. Although gas flame nudibranchs are common, they are actually rarely seen actively mating, unlike with other species.
For more details on this nudibranch, see "Nudibranchs of the Cape Peninsula and False Bay", available directly from SURG or leading Cape Town dive stores.
Nudibranch Behavior, DW Behrens, New World Publications, 2005
Nudibranchs of the Cape Peninsula and False Bay, G Zsilavecz, 2007
Nudibranchs of Southern Africa - a guide to the opisthobranch molluscs of southern Africa, T Gosliner, 1987.