Cratena affinis from Hachijo Is., Japan

July 13, 2002
From: Rie Nakano

Dear Dr.Rudman,
I found this Cratena at the edge of the rocky reef of Hachijo Island, Izu, Japan, in 28th, September, 2001.
Is this Cratena affinis

Water temperature:24.6 degrees
Frequency:uncommon in Hachijo

Rie Nakano

Nakano, R., 2002 (Jul 13) Cratena affinis from Hachijo Is., Japan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Rie,
I am sure you are right. Although the colours are rather different from the painting in Baba (1949) this fits in all major respects Baba's Hervia affinis. In particular the two large flattened rings on the rhinophores are very distinctive, and so are the inflated cerata which abruptedly end in a thin tapering papilla at the tip. Baba notes the body is covered in white spots, as is your animal, and describes the cerata as having fine, longitudinal, opaque white lines and a dark digestive gland. In your animal only traces of those lines are present and I presume the colour of the digestive gland duct is dependent on the slugs recent diet. I can't check in this photo for the presence or absence of the two orange red patches on the head, that Baba describes. On balance I would agree that this is Cratena affinis. The most appropriate genus for this species must wait until more material is examined.
Best wishes,
Bill Rudman.

Rudman,W.B., 2002 (Jul 13). Comment on Cratena affinis from Hachijo Is., Japan by Rie Nakano . [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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