Chromodoris obsoleta from Saudi Arabia

Dear George,
Thanks for this extra information on C. obsoleta. I'm afraid I can't help with any more information than is recorded on the Forum. We know very little about the marine biology of the northwestern Indian Ocean, and this species seems to be endemic to that area. As I mention on the species Fact Sheet, Gohar & Soliman (1967) describe the embryology and life history of a species they identify with C. obsoleta but from their colour description of the living animal it would seem that their animal was a species of Glossodoris, possibly G. hikuerensis.  

Your upper two photos show sponges but it is most unlikely that they are the food of this species as I think they are both species of Euryspongia, a genus of dysideid sponges not usually eaten by chromodorids. In the top photo there is a pale purple colony in the bottom right corner; and in the middle photos the animal is crawling on a whitish network, which is the fibrous skeleton of a dead colony. Your mention of fairly extreme temperature and salinity conditions suggest they may have been the cause of the death of this colony. The animals in the bottom photo are indeed mating, but if the 'tail' you mention is the yellow object, it is a small colony of a calcareous sponge. As with the other sponges, it is most unlikely that it is a food item for this species.

If this species is reasonably common there is a good chance you will find it laying an egg ribbon, or perhaps feeding or congregating on a sponge. We have another message [#12729] showing numbers of animals congregating - and presumably feeding - on a sponge colony, but unfortunately there is not enough detail in the photo to identify the sponge.

Best wishes,
Bill Rudman