Photo by Niklas von Maltzahn
Niklas and Erland spotted this floating nudibranch at the Miller's Point slipway, in between many bluebottles, and took this superb photo of it. They correctly identified it, and found out first hand that it uses the stinging cells from the bluebottles for its own defense, as Niklas was stung picking it up!
It floats upside down just under the water surface, which it does by ingesting air to stay afloat. Although more common offshore, winds can bring them inshore, and they may occasionally be found washed up on beaches.
Nudibranchs of Southern Africa - a guide to the opisthobranch molluscs of southern Africa, T Gosliner, 1987.
Two Oceans, A guide to the marine life of Southern Africa, GM Branch, CL Griffiths, ML Branch and LE Beckley, 1994.