Phanerophthalmus from Japan

November 1, 1999
From: Atsushi Ono

Dear Bill
I have found 4 color variations  of Phaneropthalmus spp at Kerama Is. [near Okinawa]. One is green and I think this is P. smaragdinus
which I haven't sent a photo of because it is in my book

The three individuals in the attached photos are maybe the same species, but I hope you can check them for me.

UPPER RIGHT: I think this is a juvenile, 5mm long, at 5m depth. This was found underside of dead coral. Its body color is dark pink, tip of head shield is white.
LOWER LEFT: This is 15-20mm long, at 3m depth, I have seen 3 individuals. This body color is dark brown, tip of head shield is white little. This has two round light patches on its head shield. I show this in my book.
LOWER RIGHT: This is similar to P. smaragdinus. Body color is dark green, 20mm long, at 3m depth.
Atsushi Ono

Ono, A., 1999 (Nov 1) Phanerophthalmus from Japan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Atsushi,
I suspect that Phanerophthalmus gets some of its body colour from the algae it is feeding on, which could explain some of the colour variation from pink to dark green. I am not sure though about the black forms. The white edging at the posterior tip of the headshield in both pink and black animals does suggest they are the same species. I have seen small pink animals and larger ones ranging from a translucent pale green to a dark greenish-black but never pure black ones like the one in your photo.

The only way to be sure if they are the same species is to have a look their anatomy to see if we can find any differences in the shape of their teeth or gizzard plates.

Best wishes,
Bill Rudman.

Rudman, W.B., 1999 (Nov 1). Comment on Phanerophthalmus from Japan by Atsushi Ono. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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