Thorunna horologia and friends?

February 16, 2009
From: Valda Fraser

Dear Bill
Why are these "critters" crawling on Thorunna horologia? I see it often.

Locality: Park Rynie, 25 m, South Africa, Indian, 6 Feb 2009, Rocky reef. Length: 12 mm. Photographer: Valda Fraser.

Best wishes

Fraser, V.J., 2009 (Feb 16) Thorunna horologia and friends?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Valda,

These 'critters' are caprellid amphipods - sometimes called 'skeleton shrimps' because of their shape. I have discussed a little bit about caprellids and their association with some nudibranchs in an earlier message [#19058] and you'll find a few more examples on the Forum if you search for caprellid.  I have enlarged a couple of sections of your photo and one of them shows that the substrate and growths, on which Thorunna is crawling, are over-run with caprellids of various sizes.  I  think this is just a coincidence. If you have seen it often then perhaps the sponges that Thorunna feed on live in a place that caprellids find attractive.

On a seperate topic, your photo gives us a nice view of the purple oral tentacles. I noted in the original description of this species that specimens I had seen had the oral tentacles 'tipped with a washy purple' so it is good to get this character confirmed, as photos usually don't show it.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Feb 16). Comment on Thorunna horologia and friends? by Valda Fraser. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


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