Siphopteron nigromarginatum? from Kii Peninsula

August 23, 2001
From: Yasuhiro Shirai

Dear Bill,
Thank you for your message. I saw Mr. Nishina's photos of Siphopteron cf. nigromarginatum. I took some photos similar to Mr. Nishina's individuals in spring of this year and last year at Tanabe Bay, Kii Peninsula. But my individuals of photos have bold marginal line. These photos are of different individuals. Are these Siphopteron nigromarginatum? If not, could you please identify them for me?

Date: May, 2000 and 2001
Place Tanabe Bay, Kii peninsula, Japan
Depth: 7 to 15m
Size: 5 to 10mm

Best Regards,
Yasuhiro Shirai

Shirai, Y., 2001 (Aug 23) Siphopteron nigromarginatum? from Kii Peninsula. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Yasuhiro,
Thanks for these photos which are indeed Siphopteron nigromarginatum. It is apparently quite variable in colour with the black parapodial border being very heavily pigmented in some animals and almost absent in others.

I don't know if you have seen the very large new book by Dr Okutani (2000) - Marine Mollusks in Japan. In it, this species is identified as Gastropteron bicornutum Baba & Tokioka, 1965, but I think this is a misidentification. In that animal the posterior visceral hump has a secondary papilla (hence the name bicornutum), and the brief colour notes in the original description mention orange spots rather than an orange background colour. There is also no mention any black pigmentation.
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Aug 23). Comment on Siphopteron nigromarginatum? from Kii Peninsula by Yasuhiro Shirai. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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