Pleurobranchus hilli - feeding observation

April 22, 2003
From: Sue Newson

Hi Bill,
I'm so glad my message was so helpful to you. The photo I sent in one of my earlier messages shows one actually feeding, clearly showing the 'bite' marks.

Thanks Sue,
Sorry, I missed the significance of the photo with the 'bite marks'. I have copied it here with a close-up of the 'bite mark.' At the risk of sounding like a policeman, can I ask if you actually saw it biting? As far as I know we have no record of Pleurobranchus hilli feeding, so the more 'weight' I can give your evidence the better. Basically an 'eye-witness account' is better than the circumstantial evidence of 'it was by the bite so it must have done it'.

Another point of interest is the object it is eating. It certainly looks like a sponge colony, but as far as I know, species of Pleurobranchus have never been observed feeding on sponges - their sole food seems to be ascidians. So if your Pleurobranchus is eating this colony then it either the first record of a Pleurobranchus eating a sponge, or the colony is an ascidian. Interestingly there is an ascidian - Didemnum spongoides Sluiter,1909 - which looks very like a sponge colony, and is often mistaken for one. It has not been recorded from New South Wales, but has been found in most of the rest of Australia and the tropical Indo-Pacific, so there is no real reason why it couldn't occur in Jervis Bay. The family Didemnidae, to which it belongs, has calcareous spicules in its skin so colonies can feel as rigid as a spiculate sponge colony so there is no easy way for you to determine whether it is a sponge or an ascidian in the field. My bet is that it is an ascidian, so it would be nice to get a confirmation of your feeding observation.
Best wishes,
Bill Rudman

Rudman, W.B., 2003 (Apr 22). Comment on Pleurobranchus hilli - feeding observation by Sue Newson. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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