Giant Sea Hare from Sydney Harbour

March 1, 2007
From: Amy Shek

Hi Bill,

I met a Giant MONSTER SEA HARE at Camp Cove, Sydney Harbour (5m depth)last Sunday(18/2/07)while diving.

I mean REALLY REALLY BIG ONE, when I saw it, I took off my fin and put it next to it and it was just about the same size as my fin (fin length: 25inches) photos attached.

Locality: Camp Cove - Sydney Harbour, 5 metres, NSW, Australia, 18 February 2007, sandy bottom. Length: 25 inches. Photographer: Amy Shek.

Could you please identify this sea hare for me?
Wonder what is the biggest size of sea hare that can grown to?

Amy Shek

Shek, A., 2007 (Mar 1) Giant Sea Hare from Sydney Harbour. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Amy,
Somewhere in the Forum I ask participants not to use CAPITALS as it is a form of internet shouting - but I guess in this case you are allowed to be a bit excited. 25 inches [= 65 cm] is definitely a large slug. Your animal is Aplysia extraordinaria which is found down the east coast of Australia, and is possibly the same as another large sea hare in Western Australia called Aplysia gigantea, which apparently grows a bit bigger. I haven't kept a record of the largest A. extraordinaria reported, but yours must be up near the biggest.

However I am afraid it has a way to go compared with Aplysia vaccaria from the west coast of North America which has been reported to grow to 99 cm [= 39 inches] in length.

Have a look at the Fact Sheets and accompnying messages for more information.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (Mar 1). Comment on Giant Sea Hare from Sydney Harbour by Amy Shek. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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