Colour variation in Chromodoris rubrocornuta

January 1, 2001
From: Scott Johnson

Hi Bill,

Here's one more for the Forum species list. Chromodoris rubrocornuta shows some interesting variation throughout the Marshall Islands atolls. The specimen e181b is one of six found beneath rocks in shallow water (3 meters or less) during an expedition to Bikini Atoll in the early 80s. The specimens, which were mostly from about 8 to 15mm in length, were all of similar color. A single specimen found at Rongelap Atoll, less than 100 miles to the east, lacked color in the rhinophores and gills (e181r). Another 150 or so miles east, two specimens at Utirik Atoll both had a bit more of the purple color in their margins (e181u). All these were found during short expeditions, but curiously, extensive collection at Enewetak Atoll over nearly three years found no specimens, although Chromodoris galactos (separate message) is quite similar in coloration. Twenty or more specimens that may also be C. rubrocornuta have been found at Kwajalein Atoll, about 200 miles south of Bikini, but they differ in having bright yellow mantles (separate message).


Johnson, S., 2001 (Jan 1) Colour variation in Chromodoris rubrocornuta. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Scott,
Now I really can't delay putting up some more of these white chromodorids with orange, yellow and reddish borders. I also promised some time ago to put up some more Hong Kong records so this is a chance to do that as well.

These are intersting photos, even if they are a little less than straightforward. Firstly the white edge to the rhinophore lamellae is interesting. I have never seen this species alive and in all the photos I have seen the rhinophore clubs appear a translucent red with no distinct white edging to the lamellae. I don't know if that means the species is variable, or the photos I have seen are not quite focussed. I must recheck my Hong Kong photos.

Secondly, I would not be surprised if 181r is Chromodoris galactos rather than a strange variant of C. rubrocornuta. I guess when we have only photos to look at its a question of which colour features you give the most weight. I feel the purplish border with small white specks is good character of C. galactos but we would need some more specimens from the same area to get some idea of local variability.
Best wishes,
Bill Rudman.

Rudman, W.B., 2001 (Jan 1). Comment on Colour variation in Chromodoris rubrocornuta by Scott Johnson. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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