Re: Cratena affinis? from Japan

December 4, 2002
From: Nishina Masayoshi

Dear Bill,
Concerning Jun Imamoto's recent message on Cratena affinis. Afterer he sent the message, he and I have tried to re-sort some animals which have similar external features.

Type A: This has almost perfect external features of C. affinis as described by Baba.

Type B: This is the same photo that J. Imamoto already sent to you. As you said the only difference is the digestive gland colour, This red digestive gland colour always appears only around the base of the cerata like that. I feel this is maybe a color variation of Type A.

Type C: [see photo below] This has different external features. The animal has no fine, longitudinal, opaque white lines on the cerata, there are white dots on the cerata or white area around the tip of the cerata instead of the lines, there is no orange or red patch on each side of the head, the body is covered in white and orange-yellow specks. The upper half of the rhinophore is white, next, an orange band continues. Perhaps, this animal and Dr.Gosliner's animal Cratena sp.1 in his book Nudibranchs of Southern Africa are the same. I also feel the shape of the cerata is bit different from Type A and Type B.

These animals are rather common on Hachijo Island and Izu Peninsula, Japan, but very difficult to find and photograph because of their small size.

Best Regards,
Nishina Masayoshi
Jun Imamoto

Masayoshi, N., 2002 (Dec 4) Re: Cratena affinis? from Japan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Nishina & Jun,
Thanks for your thoughtful observations. I would agree that your type A and B are just the result of food in the digestive gland. Concerning type C, I agree that the differences are of a more significant nature than between A & B, in particular the lack of white lines on cerata and lack of red patches on the head. However the general shape of the cerata and the body are very similar so it is possible they may turn out to be variations of one species. One thing I do notice in your photo alongside of Type C is that the flattened rings on the rhinophores seem to have been replaced by a radiating set of papillae. If you could send a photo showing this more clearly it might be useful. At present I think I will move 'Type C' to a separate page, Cratena cf. affinis, until its relationship to the more 'typical' form is determined.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Dec 4). Comment on Re: Cratena affinis? from Japan by Nishina Masayoshi. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Cratena affinis

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