Hallaxa fuscescens from Mayotte Island

September 2, 2009
From: Matthias Deuss

Dear Bill,

I found this little nudibranch moving among seagrass at low tide. It wasn't feeding. I have never seen it before, nor have I seen any picture of it, and it has not been recorded in Philibert Bidgrain's website.

Locality: Moutsoumbatsou reef, 1 metre, Mayotte Island, France, Mozambique Channel, Indian Ocean, 8 August 2009, Sand and seagrass. Length: 15 mm. Photographer: Matthias Deuss.

By the way, most of the nudibranchs I found on this reef, which is mostly covered by seagrass and seaweeds, were black or very dark, uncolored species : this one, Actinocyclus verrucosus and Dendrodoris nigra. Is it more than a coincidence ?

Thank you very much for your help,

Matthias Deuss


Deuss, M., 2009 (Sep 2) Hallaxa fuscescens from Mayotte Island. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22622

Dear Matthias,

This is Hallaxa fuscescens. In a recent message [#22626] I noted the characteristic shape of the gills in all species of Hallaxa. You can see the same goblet-shaped gill circlet in your animal as well.

Concerning finding three dull coloured species together. I am not sure if the colour similarity is significant, but these three dorids feed on sponges which can tolerate quite extreme ecological conditions. Certainly H. fuscescens can be found high on rocky shores and similarly Dendrodoris nigra can be found in luke-warm water in upper tidal pools. Shallow sea-grass beds are also not the best places for sponges but those that are found there are tough and adaptible. So I would say these three species were found together because of the adaptibilty of the sponges they feed on - but I don't know if their similar colouration is an adaptation for such conditions.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Sep 2). Comment on Hallaxa fuscescens from Mayotte Island by Matthias Deuss. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22622


Hallaxa fuscescens

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