Navanax inermis or Chelidonura hirundina ?

May 28, 2007
From: Takao Urasawa

Concerning message #19140:

Dear Dr.Bill,
Here we have two pictures.
I thought first this animal is Chelidonura hirundina but it seems to look like Navanax inermis.

Locality: Crevasse of Wing Beach, 15m, Saipan, Northern Mariana Islands, Pacific Ocean, 14 May 2007, on the bedrock. Length: 10mm. Photographer: Takao Urasawa.

Moreover, we found eggs strings on this animal.
Would you tell us your idea, please ?
Best regards,

Takao Urasawa, 2007 (May 28) Navanax inermis or Chelidonura hirundina ?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Ura,

Although I haven't seen this colour form before I am pretty sure this is Chelidonura hirundina. It certainly looks a little like Navanax inermis, but the geographic distribution of that species seems to be restricted to the west coast of central America and up into southern California. Also, just in case it is a 'hitchhiker' the sides of its head are much more lobe-like in Navanax than in your animal.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (May 28). Comment on Navanax inermis or Chelidonura hirundina ? by Takao Urasawa. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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