Glossodoris averni from Sydney

Dear Akos,
Sydney is an interesting place because it is a convergence zone between the tropical northern fauna and the southern temperate fauna. New South Wales also has an endemic fauna derived from both elements.

The number of tropical species seen each year around Sydney depends on the strength and position of the southerly currents and eddies which can bring larval stages from tropical waters. It is a perilous journey for tropical mollusc larvae. Not only do they have to survive the perils of pelagic life and brave the cooler waters, but they have to be lucky enough to find some food that they are able to eat, once they settle out of the plankton. Those with very specialised diets will be dependent on the larvae of their tropical food also making the journey south. Some years there are many tropical species found, other years very few.

Your Glossodoris averni obviously survived the traumas and grew to a large size. Only when they reach their upper size range does the mantle become so folded and ruffled as in your photo. I can't recall G.averni being found as far south as Sydney before.

Bill Rudman.