Sohgenia palauensis? from Japan

February 3, 2002
From: Shoichi Kato

Dear Dr. Bill Rudman
I run a diving shop on Hachijo Island in Japan. Hachijo lies in the Pacific Ocean about 300km south of Tokyo. The climate is temperate but a lot of sea creatures which usually live in tropical or subtropical regions inhabit the area because of the Japan Current. Since this area is close to the Ogasawara Islands, many living things of the Ogasawara series are also seen. Thus, Hachijo is a treasure house of diverse living things.

When researching sea slugs, I come across many kinds of sea slugs which are not in the illustrated reference books, and I find it difficult to identify them. I understand that you are an expert in this area, so I'm hoping you could help me.

Here is a photo of one of the animals I can't identify. Mr Ono of Kerama islands said it is a sacoglossan.
Depth 5m, length 8mm, photographed only once at a shallow reef.

Shoichi Kato

Kato, S., 2002 (Feb 3) Sohgenia palauensis? from Japan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Shoichi,
This is an interesting animal. I think it is probably Sohgenia palauensis a species which has only been reported from the Palau Ids. It is closely related to the species of Cyerce and Polybranchia. I can't be totally certain of the identification because the only description I have seen of it is the original one by Dr Hamatani. His specimen did not have brown spots as in your specimen and the cerata were never as large as in your animal but it is possible that the colour is a bit variable in this species and it is also possible that some of the larger cerata in Hamatani's animal had dropped off before he had a chance to examine the animal.

Have a look at Hamatani's drawing and his description which I have included in the Fact Sheet for this species.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Feb 3). Comment on Sohgenia palauensis? from Japan by Shoichi Kato. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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