Sea pens

March 9, 2010
From: Jan Kocian

Hello Bill.

Concerning your request for a photo [message #23252], here are some Orange sea pens - Ptilosarcus gurneyi from the Eastern Pacific, for the sea pen page. The second photo illustrates what happens to them when a hungry horde of Armina californica picks one of them for lunch.

Locality: Possession Point beach,Whidbey Island, 50 feet, California, Eastern Pacific Ocean, 19 August 2009, Sandy slope. Photographer: Jan Kocian.

Jan Kocian

Kocian, J, 2010 (Mar 9) Sea pens. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Jan,

Thanks very much. I thought it would be sad to have a photo of a dead or dying sea pen to represent them, so your photo of a proud group of them standing tall is just what I wanted.

Not that your message contains a happy ending, but it well illustrates just how specialised many nudibranchs have become. Having such a specialised diet can be an advantage when the food is plentiful, but it does mean that if the sea pen population disappears for some reason the Armina population will starve.

Best wishes,
Bill Rudman

Rudman, W.B., 2010 (Mar 9). Comment on Sea pens by Jan Kocian. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Armina californica

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