Aphelodoris varia gills, Bare Island, Sydney
© John Turnbull
"Nudibranch" means "naked gills". This photo shows the branchia or exposed gills of the variable dorid nudibranch. This organ is used to exchange O2 for CO2 just like gills in fish and lungs in mammals. The branched structure and fine "leaves" maximise surface area for the exchange. It can be retracted if the animal feels threatened.
Photo taken on 5 Dec 2014
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