Marionia eating Gymnodoris aurita ?

Dear Nonoy,
I am not sure if your message is in reponse to Dave Behrens' message [#16478] or a remarkable coincidence. Your photo certainly shows that one species is biting the other but sometimes it is difficult to be sure who is biting who - particularly when the bite is mouth to mouth like this. If the one being eaten retracts its head when it is bitten, it can draw the head of the attacker into the retracted part of its body so that it looks as though the one being bitten is engulfing the attacker.

I am not sure that this is what your photo shows, but species of Gymnodoris are well-known eaters of other opisthobranchs, and Gymnodoris aurita is known to eat tritoniids such as Marionia. My first thought is that what we are seeing is the Gymnodoris, after biting the head of the tritoniid, being temporarily drawn into the body of the tritoniid which has retracted its head in reaction to the bite.

I would be interested in seeing any other photos you have of the incident to see if we can work out what is going on. Tritoniids usually feed on soft corals.
Best wishes,
Bill Rudman