Favorinus from Okinawa

September 4, 1998
From: Bob Bolland

Bill,
Here is a scan of a delightful aeolid (Favorinus?) from Okinawa. This is the first time I've seen this beautiful animal. It was collected by US Navy Cmdr. Keven Reed on 7 June, 1998 from Horseshoe Cliffs in 21 plus meters. The animal was found on a Hexabranchus egg ribbon. According to Keven, at the time the animal was collected, the rhinophores were the same color as the cerata. The animal was then placed in a home aquarium until it was given to me twelve days later, whereupon I took the accompanying photograph. The rhinophores changed from red to black from the time it was collected until the time it was photographed (TL: 22mm). I'm not sure whether the color change was rapid or done in slow increments.

Was the color change due to stress from within the aquarium, or do other factors play a roll in this?
Bob Bolland
OKINAWA, 21 August 1998

bolland@imicom.or.jp

Bolland, R.F., 1998 (Sep 4) Favorinus from Okinawa. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/224

Note added 26 July 2002: I think this is probably a colour form of Favorinus mirabilis and have moved messages concerning Favorinus sp. 2 and Favorinus sp. 6 to Favorinus cf. mirabilis page.

Dear Bob,
It certainly looks like a Favorinus and being on another opisthobranch's eggs is a pretty good sign its a Favorinus, for as you know opisthobranch egg eating is a characteristic of the genus. Its black ridged rhinophores certainly look a bit like those of Favorinus tsuruganus Baba & Abe, 1964, but that species is essentially yellow with black-tipped cerata.

Concerning colour changes. Some species such as Favorinus japonicus change colour depending on the colour of the eggs they are feeding on. But the colour change is due to the colour change of the gut contents not the skin pigment. As the rhinophore colour is probably skin pigmentation I'm not sure why it changed to black.
Bill Rudman

Rudman, W.B., 1998 (Sep 4). Comment on Favorinus from Okinawa by Bob Bolland. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/224

Factsheet

Favorinus cf. mirabilis

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