Bonisa and Janolus from S. Africa

March 10, 2004
From: Sakkie du Preez


Dear Bill
I have a couple of questions regarding Janolus capensis and Bonisa nakaza that I hope you could help with.

Upper photo:
In October 2003, on a night dive, we found these two huddling together, not that the water was that cold... Anyway, my dive buddy, Annemarie took the photo. We found them on Bell Buoy Reef, Port Elizabeth South Africa, in about 12m of water. Are they both Janolus capensis or is the one with the purple cerata Bonisa nakaza?

Lower photo: And then, eh-hum Dr Rudman, what are the two Janolus capensis up to at the top of the photo? As far as I can see; it looks like the other one is blushing ... I found lots of these parties of 2-4 nudi's on Riy banks at a depth of about 21m. The reef is about 20km out to sea from Port Elizabeth.

Best regards
Sakkie du Preez

Sakkie.DuPreez@comau.co.za

du Preez, S., 2004 (Mar 10) Bonisa and Janolus from S. Africa. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/12373

Dear Sakkie,
Both the animals in the top photo are Bonisa nakasa and those in the bottom one Janolus capensis. I understand that B. nakasa is quite variable in colour but you'll note that in Janolus capensis the white pigment on the cerata covers most of the outer side and only the tip of the inner side while in Bonisa nakasa, the white, if present, only occurs at the tip. More importantly, Janolus has a large inter-rhinophoral crest [caruncle] as you can see in an earlier photo [#11177] and there is no sign of it in the paler animal.

It is also unlikely that you will find them together because they feed on different bryozoans. It is of course possible that you might have a mixed growth of bryozoans, but on the balance of probabilities I think they are both Bonisa. Concerning the lower photo - as you subtly suggest, the upper two animals are mating.

Best wishes
Bill Rudman

Rudman, W.B., 2004 (Mar 10). Comment on Bonisa and Janolus from S. Africa by Sakkie du Preez. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/12373

Factsheet

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