Plakobranchus variation - how many species?

June 8, 2005
From: Atsushi Ono

Dear Bill,
There is short Japanese report (Yamasu, 1997) which refers to the possibility that  Plakobranchus ocellatus may consist of more than one species on the main Okinawa island. However, photographs of dorsal view are not so clear in this report and there are no photograph of the foot.

Since then, I have observed many Plakobranchus ocellatus in Kerama Is. They seem to be divided into five forms. A,C and D are seen in the same area - shallow lagoon. These results do not necessarily correspond to Yamasu, 1997. In addition, another form was found on both the main Okinawa island and Amami Oshima Is. [See separate message #13878 from Jun Imamoto]. I think that the pattern on the foot is especially important. I think that these different 'forms' suggest more research is required to determine how many species there actually are.

The colour patterns are posted as separate messages:
Var. A = message #13979
Var. B = message #13980
Var. C = message #13981
Var. D = message #13982
Var. E = message #13983
Var. F = message #13878

Sincerely,
Atsushi Ono

ononini@cosmos.ne.jp

Ono, A., 2005 (Jun 8) Plakobranchus variation - how many species?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/13970

Dear Atsushi,
Thanks for this interesting contribution. Can you give me a reference to Yamasu's publication please? I am sure many of us have noticed the variability in Plakobranchus so it is nice to have it sorted out in this way. Many names have been given to Plakobranchus so if it is shown in the future that there is more than one species, I hope the old names were well enough described to allow us to decide which name refers to which colour 'variation'.

I agree that the colour on the sole of the foot is interesting. I also noticed when looking at your photos that in some the green network of digestive gland tubules are clearly visible on the underside of the head in some but not others. I have often wondered if variability in this species - at least dorsally is cirrelated with the environment. For example are those living in white coral sand always very white so they are well camouflaged, and do those living in more muddy environments have a darker appearance. Also chloroplast symbiosis is an important aspect of their biology. Perhaps colour variability is associated with the needs of the chloroplasts?

I suspect this relatively common species, or group of species, has many secrets for us to unravel.
Best wishes,
Bill Rudman

Rudman, W.B., 2005 (Jun 8). Comment on Plakobranchus variation - how many species? by Atsushi Ono. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/13970

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