Gastropteron from Japan

May 29, 2002
From: Atsushi Ono

Dear Bill,
About "Hopkinsia? or Okenia?". I'm sorry I did not count their appendages. I also should have use my both hands ....

I think attached is Siphopteron citrinum. This species has long pointed posterior projection.
Is this idea right?

3mm long, at 5m depth, Kerama Is. near Okinawa Japan.
Atsushi Ono

Ono, A., 2002 (May 29) Gastropteron from Japan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Atsushi,
I suspect this may be the same as your Siphopteron sp. 2. Certainly it is very similar in body shape, and lacks any colour pattern. Siphopteron citrinum (Carlson & Hoff, 1974) from the original description seems to be a more elongate species with the posterior flagellum being dorsally placed rather than posteriorly as in your animal. Also in S. citrinum the the animal has a distinctly golden yellow colour, and the posterior flagellum and the tip of the siphon are dark brown or black.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (May 29). Comment on Gastropteron from Japan by Atsushi Ono. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Siphopteron sp. 2.

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  1. Another photo of Siphopteron sp. 2.
    From: Atsushi Ono, July 28, 1999
  2. Another Siphopteron sp. from Kerama Is
    From: Atsushi Ono, July 26, 1999

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