If you think tiny marine molluscs are a bit of a yawn, then you haven't encountered Robert Burn.
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While the soft-bodied sea creatures known as nudibranchs may sit at the bottom of the food chain, according to Mr Burn, they are very clever.
For a start these striking "butterflies of the sea" are hermaphroditic – meaning they have male and female reproductive organs.
They also have eyes without lenses. And their external gills inspired their name: nudus meaning naked and brankhia meaning lungs.
"They are captivating, I find them quite fascinating," he said.
Just shy of 79, Mr Burn has identified almost 100 species of the marine creature which are completely new to science.
But he's no scientist. By training Mr Burn is a builder. His family have been builders in Geelong more more than a century. It's just that over the years – without intending to – Mr Burn has become a world expert in the marine molluscs that call the waters around Port Phillip Bay, Western Port Bay and Bass Strait home.
"It's a hobby," Mr Burn said. "But over the years it has become an obsessive hobby."
An honorary associate at Museum Victoria, he has co-authored around 100 papers in scientific journals over the past 60 years and contributed chapters to books on marine life. But Mr Burn's latest book, a nudibranch field guide released in February by Museum Victoria and CSIRO Publishing, is his first as a sole author.
The glossy photographs show off the creatures' beauty, with many looking like they'd be just as at home in a Mardi Gras parade as on the sea floor. They come in all colours; from fluorescent orange and purple to opaque white with delicate dots of white pigment. Some have strong, snail-like shells while others are soft and jelly-like.
More than 400 species of nudibranchs occur in south-eastern Australia and Mr Burn estimates there are at least another 100 still to be identified.
Nudibranchs range in size from a few millimetres to 40 centimetres long. Best spotted in early morning and late evening, they live in shallow rock pools as well as ocean waters to depths of more than 6000 metres.
Not being a scuba diver, Mr Burn concentrates on the shallow waters, where he inspects rock pools. A microscope, pencil and paper are always handy, so he can sketch what he sees.
Among his most satisfying finds was in 1960 when he documented two spring-leaf, green-coloured nudibranchs that previously had only been documented in the fossil record. This was the first time they had been found alive in Australian waters – and he found two different types. Both on the same day during a field trip at Point Danger in Torquay.
"It is satisfying when you find something that is of great interest to international marine biologists," he said.