Chromodoris geometrica - Phyllidiid mimic

October 7, 2005
From: Paul Osmond


I found this group of I believe phyllidiid nudibranchs on a night dive on Flinders Reef off the coast of Townsville in Queensland, Australia. I haven't been able to figure an exact species (or even if I am looking in the right direction) so any help is appreciated.

There was roughly 10 individuals in a small area, all about an inch in size. We were roughly in 15m of water.


Osmond, P., 2005 (Oct 7) Chromodoris geometrica - Phyllidiid mimic. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Paul,

This is Chromodoris geometrica. No great shame in thinking it is a phyllidiid. It is one of the classic phyllidiid mimics - but the circlet of gills tends to sabotage its mimicry.

You would think that a cluster of animals together like this would mean it would be easy to find what its favourite sponge food was. These photos are cropped versions of 6 or 7 of yours which I searched diligently for signs of an identifiable sponge, but they show no more than the ones I am posting - which is nothing! All I can say is that they have eaten the sponge out, or else it is partially overgrown by other growths. I am not desperate to know what sponge it feeds on as I have records of it on the purple sponge Chelonaplysilla violacea, but it well illustrates how difficult it is to build up feeding information on these animals.

Best wishes
Bill Rudman

Rudman, W.B., 2005 (Oct 7). Comment on Chromodoris geometrica - Phyllidiid mimic by Paul Osmond. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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