Siphopteron flavum? from Japan

March 1, 2000
From: Yasuhiro Shirai

Dear Bill,
Thank you for your reply about Siphopteron fuscum.
This time, I attach 2 photos which I thought were Siphopteron fuscum. But these animals are different color.

Could you please identify it for me?

Location: Shima Pref. Mie, Japan (Kii Peninsula, east coast)
Length: 10mm
Water temperature: 14C
Date Feb.2000
Depth: 2-3m
Crawling on rock or crawling on seaweed.

Best regards,
Yasuhiro Shirai

Yasuhiro Shirai, 2000 (Mar 1) Siphopteron flavum? from Japan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Yasuhiro,
Firstly, the animal I identified as S. fuscum is almost identical to the original description, so I am pretty sure that it is correctly identified. I have seen some published photos [See Atsushi Ono's Opisthobranchs of Kerama Islands in which the dark brown background colour can be a very pale yellowish brown.

In your photos, the short, blunt, posterior projection is very similar to that described for Siphopteron flavum (Tokioka & Baba, 1964). That animal was described as "bright chrome yellow, and minutely dotted with white. The posterior edge of cephalic shield is ivory black... as is posterior protuberance"

In a later publication (Baba & Tokioka, 1965) another specimen is described as lemon yellow and with reddish-purple rather than the black of first specimen. There is also a reddish purple spot on the posterior shield.

Carlson & Hoff (1974) report on 600 specimens they have observed in Guam and they describe the colour as yellow with bright white spots scattered over the dorsum and parapodia. In their specimens the parapodia are lined with dark brown as is the back edge of the funnel. the dorso-median crest and posterior protuberance are tipped in black.

If the Guam animals are the same as the Japanese specimens then the species is quite variable in colour.

Yasuhiro's animals have elements of both descriptions and they look a bit different from Atsushi Ono's photos at the top of this page. Any opinions or information on the colour variation, and the length of the posterior flagellum within S. flavum would be very welcome.

Best wishes,
Bill Rudman.

Rudman, W.B., 2000 (Mar 1). Comment on Siphopteron flavum? from Japan by Yasuhiro Shirai. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Siphopteron flavum

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