Phyllidia coelestis mating

July 30, 2008
From: Leanne & David Atkinson

Concerning message #9399:

Dear Bill,
Thought we'd send this after your recent comment that the forum doesn't have many photos of Phyllidiids mating. We think this is Phyllidia varicosa mating. You do already have Mary Jane's shot but it doesn't show as much of the genitals as these photos do. Because they are clear we didn't notice the genitals until we put the photo on the computer. The two photos are the same animals from diffferent angles. We thought they were feeding and took the different angles to try to confirm it.

Locality: White Rock, Moso Island, 15 metres, Vanuatu, Pacific, 22 April 2008, Coral Reef. Length: 40 mm approximately. Photographer: Leanne & David Atkinson.

It is also a possible addition to the range since we couldn't see a message with animals from Vanuatu.They were one of the most common nudibranchs for us to find both on this trip in April and the one in July last year. The water temperature was a very comfortable 29 degrees celcius. Can you confirm the identity?

Leanne & David Atkinson

Atkinson, L. & D., 2008 (Jul 30) Phyllidia coelestis mating. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Leanne & David,

Thanks for this nice observation. However the animals are in fact Phyllidia coelestis. One clue to its identity is the the median black band on the mantle which is broken by the yellow-tipped tubercles. In P. varicosa there is a bluish ridge down the dorsal midline with black bands on either side.

Best wishes,
Bill Rudman

Rudman, W.B., 2008 (Jul 30). Comment on Phyllidia coelestis mating by Leanne & David Atkinson. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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