July 12, 2003
From: Rokus Groeneveld
On the 13th of April 2002 I was on a nightdive on the housereef (Torfa)in Wahdi Lahmi (400 km south of Hurghada, Egypt). I found two small (about 10mm) what I think are nudibranches on the eggs of a Hexabranchus sanguineus.
From what I understand of all the pictures of juvenile Spanish Dancers on this site they're not that.
But then what are they? I'd be very pleased if someone could help me out?
firstname.lastname@example.orgGroeneveld, R., 2003 (Jul 12) Favorinus on Hexabranchus eggs. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/9863
You are quite right - they are not juvenile Hexabranchus. They are in fact an aeolid nudibranch of the genus Favorinus which specialise on feeding on the eggs of other sea slugs. Although some species of Favorinus apparently specialise on the egg ribbons of particular species, others like Favorinus japonicus, eat a wide variety of egg masses. Because a duct of their gut extends up into each of the cerata on their backs, they chnage colour depending on the colour of the eggs they are eating. As in your photo they are therefore well camouflaged when feeding on and egg ribbon. From the two swellings on their head tentacles or rhinophores I am pretty sure your animals are Favorinus japonicus. Two other species, Favorinus mirabilis and Favorinus cf. mirabilis, feed on Hexabranchus eggs but their rhinophores are quite different in shape.
Favorinus japonicus from Reunion Island
From: Hugues Flodrops, March 31, 2009
Favorinus japonicus on Hexabranchus eggs
From: Colin Ogden, September 25, 2007
More photos of Favorinus japonicus
From: Dong Bum Koh, May 10, 2005
Favorinus japonicus and F. tsuruganus together
From: Dong Bum Koh, May 3, 2005
Re: Favorinus eating Hexabranchus eggs
From: Yves Coze, December 1, 2003
Favorinus? from Zushi, Japan
From: Akira Kurabayashi, November 16, 2003
Favorinus eating Hexabranchus eggs
From: Yves Coze, September 5, 2003
Re: Favorinus japonicus secondary metabolites
From: Jennifer Sneed, March 8, 2002
Favorinus japonicus secondary metabolites
From: Jennifer Sneed, March 6, 2002
Favorinus japonicus from Heron Island
From: Julie Marshall, March 5, 2000
Favorinus japonicus from Sulawesi
From: Lindsay Warren, February 27, 2000
Egg Predation - Favorinus japonicus
From: Bill Rudman, April 25, 1998