Is this Polycera hedgpethi?

September 27, 2005
From: Chris Cunnold

Dear Bill,
I came across this very bad photo from my very first underwater photo effort in January 2004. Is this Polycera hedgepethi? I've scanned all the books and cannot come up with anything else. If so, is it the rare find in Western Australia that all the books say it is?

Locality: Cockburn Sound, Western Australia, on Jetty Pylons. Depth: 6 m.
Length: 2.5 cm. 24 January 2004. Photographer: Chris Cunnold


Cunnold, C., 2005 (Sep 27) Is this Polycera hedgpethi?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Chris,
Yes this is Polycera hedgpethi, quite dark but definitely that species. It is a bit hard to say if it is rare or common anywhere it is found because it is a not a 'stay-at-home' species. It is totally dependent on a particular bryozoan species on which it feeds. That bryozoan, Bugula, is what we call a fouling organism because it 'fouls' the bottom of boats. Fouling organisms usually have larvae in the plankton all the time and they are the first organisms to settle out of the plankton when a clean space becomes available on the sea bed, or boat's bottom, wharf pile, etc. They then grow to maturity bery quickly before they are eaten or crowded out by some other organism, which is a bit slower to settle but for various reasons is better at pushing out competitors was it gets going. So a fouling organism's main characteristics are its ability to quickly settle when a space becomes available, and then a rapid growth to maturity and production of the next generation and a short life. Animals which feed on fouling organisms, out of necessity have much the same life cycle. So its usually feast or famine. That's why you may find large populations of Polycera hedgpethi at a particular spot for a short period, and then none for years. I don't think describing that as 'rare' means much. perhaps 'intermittent' or 'spasmodic' would be better terms.
Best wishes,
Bill Rudman

Rudman, W.B., 2005 (Sep 27). Comment on Is this Polycera hedgpethi? by Chris Cunnold. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Polycera hedgpethi

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