Thecacera pennigera? from Japan

September 13, 2001
From: Jun Imamoto


Dear Bill
Are these sea slugs both Thecacera pennigera? These sea slugs were seen in the same place at the same time.

But, I am at a loss to understand why they are both considerted the same species when their colour pattern is so different.

This sea slug can be seen in large numbers every year from March to June, so I will be able to be observe them better next year.

UPPER PHOTO: Izu Osezaki (Suruga Bay, Japan)
Depth: 18m., Size: about 25-30mm., May 4, 2001., Water temperature: 18C degrees.

LOWER PHOTO: Izu Osezaki (Suruga Bay, Japan)
Depth: 26m., Size: about 20-25mm., May 4, 2001., Water temperature: 18C degrees.

Best Regards,
Jun Imamoto

imamoto@wips.co.jp

Imamoto, J., 2001 (Sep 13) Thecacera pennigera? from Japan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5212

Dear Jun,
You certainly ask some interesting questions. If you look at my photo of an animal from Australia, at the top of the page, you will see its colour is a mixture of both your photos. It has orange, rather than yellow, spots as in your upper photo, but it has yellow-tipped rhinophores like your lower photo.

In Australia, this species varies in colour from animals like in your photos to ones which have a much more densely arranged cover of small orange and black spots, which is the colour form found in Europe. A good photo of it is in the Armstrong's message from New Zealand. I would be interested to know whether you also find this colour form in Japan.

The reason we consider all these colour forms to be the same species is that they seem to merge from one to the other. Perhaps further studies will show there are two species, but at present there is no evidence to support this idea.
Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Sep 13). Comment on Thecacera pennigera? from Japan by Jun Imamoto. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/5212

Factsheet

Thecacera pennigera

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