Janolus capensis or Bonisa nakaza

Dear Wilhelm,
I have no personal experience of these species so I am relying on what I can find in publications. As you suggest, at first sight it looks like Janolus capensis, but it could be a colour form of Bonisa nakaza. One major external difference between the two is that Janolus has a large wrinkled ridge (caruncle) between the rhinophores while in Bonisa it is much less prominent. In your photo [see lower right enlargement] there is no sign of the caruncle which I would expect to see even though it is partially obscured. The other major difference is that in Janolus, there is a digestive gland duct in each ceras, while this is absent in Bonisa. I think the reddish-brown colour in the base of the cerata in your photo is the colour of the body fluids rather than an indication of a digestive gland duct. If you look at your separate photo of Janolus capensis [message #14114] you will see the similarly coloured branch of the digestive gland is much narrower, not filling all the space in the ceras. I suspect therefore that your animal is most probably a form of Bonisa nakaza. I would appreciate a comment from Terry Gosliner.

In Terry Gosliner's publication on these animals he identifies the food bryozoans of both these species. Janolus capensis is reported to feed on Menipea triseriata and Onchoporella buskii and Bonisa on Tubucellaria levinseni. I therefore sent your photos to Dennis Gordon, a bryozoologist in New Zealand to see if he could identify the bryozoans, and he sent them on to Wayne Florence, an expert in Sth Africa, who has identified the bryozoan in the photo alongside as a soon to be named new species of Thalamoporella. So when we confirm this animal's identification we have a possible new food identification as well. As I will mention in your separate message [#14113], the typical Bonisa nakaza is on another species of bryozoan.
Best wishes,
Bill Rudman