Bornella japonica? from the Marshall Islands

May 25, 2007
From: Scott Johnson

Hi Bill,

I have been slowly putting photos of the opisthobranchs of the Marshalls on my web site and have just worked my way to Bornella. While preparing a page for a species I hadn't yet identified, I noticed it kind of matches Baba's original description of Bornella japonica. The white dorsolateral processes form three pairs, plus a couple of small single processes near the posterior end. The processes could be described, as Baba does, as bifid at the tips with smaller points around the base (although Baba reported just two smaller points while our specimen has three or four). The rhinophore sheaths have 4 or 5 supra-marginal papillae, the posterior one of which is larger and bifid or trifid, much the same as Bornella japonica. However, the appearance of the animal doesn't quite match the other photos of Bornella japonica on the Forum from Japan.

So far we have found but a single specimen here at Kwajalein Atoll, and it was in the groove and spur system on the windward leeward reef. For a few weeks a year during the doldrums, it gets calm enough to dive this side of the reef, and after a dive or two in deeper water down the slope, we often (when the swell is down) spend our last tank in the groove and spur zone, right about where the large waves crash most of the year and with the deeper grooves only 3 to 5 meters deep. It is a surprisingly productive zone, with lots of schools of fish, a bushy pink stylasterid coral growing thickly in the ledges, and lots of sponges and hydroids. Our Bornella was up in one of the ledges. How an animal like our little Bornella can even hold on during the normally surgy conditions in this area is mystifying. Yet, this zone is also the best area in the atoll for Glossodoris rufomarginata, G. atromarginata, Pteraeolidia ianthina, and Flabellina exoptata. These little guys are tougher than they look.

Locality: Kwajalein Atoll, 4 meters, Marshall Islands, Pacific, 21 Sept 2003, coral reef. Length: 25mm. Photographer: Scott Johnson

Scott Johnson

Johnson, S., 2007 (May 25) Bornella japonica? from the Marshall Islands. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Scott,

Thanks for this.  Unfortunately many of the descriptions of species of Bornella appear difficult to interpret. It seems subtleties of ceratal and rhinophore shape are quite important - much more important than general colour pattern.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (May 25). Comment on Bornella japonica? from the Marshall Islands by Scott Johnson. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Bornella japonica

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