Phestilla melanobrachia from Indonesia

November 25, 2009
From: Helene Caillaud

Hello,

Here is a picture of a nudibranch, that i'm trying to identify.

I'm hesitating between Phyllodesmium briareum or Phestilla melanobrachia. Could you help me to identify it

Locality: Bali, 20 metres, Indonesia, 8 october 2009, sandy area, muck dive. Length: 30 mm. Photographer: Helene Caillaud.

Thank you very much,

Helene,
from France

contact.helene.caillaud@gmail.com

Caillaud, H., 2009 (Nov 25) Phestilla melanobrachia from Indonesia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22836

Dear Helene,

This is the black colour form of Phestilla melanobrachia which gave the species its name [melano = black]. I think the very blue look is caused by the way light is bent by the fine cilia on the cerata - you get a similar effect with black velvet cloth.

We usually think of this species as bright orange, but when they feed on the black form of the coral Tubastraea the digestive gland in their cerata fills up with black material. However, as we can see in the close-up, the orange pigment on the rhinophores and oral tentacles stays orange as it is based on skin pigment. As I discuss elsewhere on the forum [see coral feeding] species of Phestilla drop their cerata as a defensive strategy. In the close-up you can see two rows of small replacement cerata growing amongst the full size ones.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Nov 25). Comment on Phestilla melanobrachia from Indonesia by Helene Caillaud. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22836

Factsheet

Phestilla melanobrachia

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