Chromodoris willani & C. magnifica feeding

February 23, 2009
From: Patricia Dilworth

Hi Bill,

I suspect you have photos of Chromodoris willani and C. magnifica eating, but we are always on the lookout for these "action" pictures for you!

Locality: Raja Ampat , 50 ft., Indonesia, Banda Sea, 15 November 2008, reef. Photographer: Patty Dilworth.

Thanks,
Patty Dilworth

padilworth@aol.com

Patty Dilworth, 2009 (Feb 23) Chromodoris willani & C. magnifica feeding. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22273

Dear Patty,

Action photos are always welcome and it does not matter if we already have photos of the same animal feeding. In fact it is best we have multiple observations because then we can be more confident that the food item is a normal part of the diet rather than a strange one-off activity.

Concerning the species. The upper one is certainly C. willani, but the lower one is Chromdoris annae. There are a number of similarly coloured species but one sure way to identify C. annae are the small dark specks all over the bluish parts of the mantle, which can be seen in the close-up alongside. Also in the close-up we can see a large cavity in the sponge just above the slug, which certainly looks like feeding damage.

This dark grey sponge is almost certainly a species of Petrosaspongia, which both species have been reported on before [see messages #12039; #12040; #12005; #16257]. Your photo then is valuable confirmation of the food choice of these two species. Finding two similarly coloured species together on the same food sponge is also interesting because it suggests why there are these groups of similarly coloured species. I have described a group of red-spotted species on a separate page and explain how I think that these groups of similarly coloured species living in close geographic proximity have evolved to warn predators to leave that colour pattern alone. I suspect that these more widely spread black-lined species also 'teach' predators to leave their colour pattern alone by grouping together on the same food sponges. In this way all the black-lined species would share the load of 'teaching' predators that black-lined slugs contain extremly distasteful chemicals and aren't worth biting.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Feb 23). Comment on Chromodoris willani & C. magnifica feeding by Patricia Dilworth. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22273

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