Dear Wilhelm,
The large caruncle between the rhinophores is probably the best bet but as you can't see that in many photos it doesn't help much. I don't think how flattened the cerata are is a good thing to use as their shape is fairly plastic. One very important feature though is whether there is a branch of the digestive gland in the cerata. There is  branch in species of Janolus, but not in species of Bonisa. In your photo here the reedish-brown branch, which forks near the tip is quite visible.
Best wishes,
Bill Rudman

Thanks Charles,
This animal is indeed laying its eggs. What looks like a tangle in your photo will look like the ribbon in your earlier message when it is complete. I have included a 'scenic' shot alongside as I am very impressed with the way many of your animals seem to prepare to be photographed by arranging themselve in very photogenic biotopes. I sometimes wish I could include larger images with more background but that would be hugely expensive.
Best wishes
Bill Rudman

Thanks Charles,
Good shot of the caruncle. I wish I could tell you what its function is but as far as I know its function is still unknown. You will see it described as 'sensory' but I don't know of any evidence to support that assumption
Best wishes
Bill Rudman

Dear Charles,
I think this is the same species as in your
accompanying message - Janolus capensis. It feeds on arborescent [= plant-like] bryozoan colonies like the one you can see in the left side of the closeup [lower left] I have added to your message. I have also added a closeup to the right of my reply showing the rhinophores. One characteristic of the genus Janolus is that there is a wrinkled ridge [caruncle] between the rhinophores. I can't see any sign of it in your photo and unfortunately one of the cerata is just in the wrong place. Perhaps you have another photo which shows the space on the head between the rhinophores. It would be nice to know if the 'caruncle' is present
Best wishes
Bill Rudman

Dear Charles,
I am pretty sure this is Janolus capensis, which according to Terry Gosliner is quite common throughout the year on both the Atlantic and Pacific coasts of the Cape Peninsula. I was not sure if the egg ribbon in your photo was related to the slug, but from Terry's description of the egg ribbon as 'highly convoluted' I would suspect the egg ribbon may well belong to this slug
Best wishes
Bill Rudman

Dear Rudolph,
The animals in your photos are both species of Janolus, part of a family of nudibranchs which feed on bryozoans. There are two very similarly looking species from South Africa, Janolus capensis and Janolus longidentatus. I am not sure which species these are, or if both photos are of the same species. There are good anatomical differences between the species, and their egg masses are quite different, but unfortunately there general appearance is very similar. Gosliner does say that in J. capensis the anterior end of the head is conical, while in J. longidentatus it is rounded, but unfortunately this can't be see in your photos.

In your upper photo the brown ducts of the digestive gland seem to branch near the base, which is what happens in J. longidentatus, and in the lower photo the crest between the rhinophores is white, which is what has been described for J. capensis, so it is possible that you have both species here, because they are both recorded to feed on the bryozoan Menipea. At this stage I am not sure of the identity of the other photos on this page either, but have decided to leave them all as J. capensis.
Best wishes,
Bill Rudman

Dear Erwin,
I think this is Janolus capensis, which according to Terry Gosliner is one of the common zephyrinids in the Cape Peninsula region of South Africa. There seem to be few external differences between this species and another South African species, Janolus longidentatus Gosliner, 1981, but J. capensis has a white edge to the foot which is visible in Guido's photo.
Best wishes,
Bill Rudman

Dear Valda,
I think it is Janolus capensis but i must say my opinion is not very expert on South African janolids especially when Terry Gosliner says there are few external differences between Janous capensis and Janolus longidentatus Gosliner, 1981. One feature mentioned by Gosliner (1981) is that J. capensis has a translucent whitish body with a white edge to the foot, which can certainly be seen in the lower photo. Another useful character is the shape of the egg mass and the number of eggs per capsule. Have a look at my notes at the top of the page. A photo of any eggs would be a nice thing to add.

Best wishes,
Bill Rudman.