Mexichromis macropus found sthn Queensland

January 15, 2009
From: Gary Cobb

Hi Bill and Everyone!
Please find photos of the ever-so-beautiful Mexichromis macropus found here between Noosa and Moreton Island. This species has been found about 20 times in 6 years. The photos attached are from a double dive I did on the HMAS Brisbane wreck. 6 animals were found and one was quite large.

This is the first time I have seen this species on the wreck. I assume the right food source must be growing on the wreck now. On previous dives I have seen Hyselodoris jacksoni as quite common, but now there are none to be seen. Another species that was seen 4 times on the same dives was Tambja morosa.

Locality: Mooloolaba, Sunshine Coast, 18 m, Queensland, Australia, Pacific Ocean, 08 January 2009, Subtidal. Length: 15-30 mm. Photographer: Gary Cobb.


Cobb, G.C., 2009 (Jan 15) Mexichromis macropus found sthn Queensland. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Gary,
The right food source you wonder about is indeed present. It is the bluish - purplish sponge the animals are sitting on. It is a species of Euryspongia which appears to be the main - perhaps only - food choice of  Mexichromis macropus.

In the black background photo we can see the large white spherical glands   embedded in the mantle skirt around the posterior end of the mantle, so typical of species of Mexichromis. These white sacs store distasteful  molecules from its food sponge which it uses to deter potential predators. As different groups of sponges have different anti-feedant molecules, we can get clues to the likely food of sponge-feeding nudibranchs by investigating the molecules the nudibranchs have stored in their mantle.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Jan 15). Comment on Mexichromis macropus found sthn Queensland by Gary Cobb. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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