Melibe australis - ascidian mimic

March 1, 2003
From: Bill Rudman

In specimens of Melibe australis without much pigmentation, it is difficult to see the characteristic shape of the cerata in this species. The cerata are stalked and flask-shaped or top-shaped [see lower left photo]. While the underside of each ceras is smooth, the dorsal side is covered in large transparent papillae which often appear to be invisible because of their transparency. In animals with a bright opaque background colour, such as the orange one in the upper right photo, the cerata seem to be covered in wide holes similar to the oscules of sponges or siphonal openings of ascidians. This is an optical illusion, each white-ringed 'hole' being in fact the base of a transparent papilla or elongate tubercle.

When the animals are not crawling, and the cerata are tucked together, they have a remarkable resemblance to to orange, pink and whitish colonies of a compound ascidian also found on the shore at Arrawarra. A photo of it can be seen at the top of the Velutinidae Fact Sheet.

Photos:: Arrawarra Rock platform, Woolgoolga, Northern New South Wales. 3 Dec 1990 At LWS. Numerous specimens (approx. 28 mm long) AM C164561. Photos: Bill Rudman

Best wishes,
Bill Rudman

Rudman, W.B., 2003 (Mar 1) Melibe australis - ascidian mimic. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Melibe australis

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